A TEXT-BOOK OF Volumetric Analysis WITH SPECIAL REFERENCE TO THE VOLUMETRIC PROCESSES OF THE PHARMACOPOEIA OF THE UNITED STATES. DESIGNED EOR THE USE OF PHARMACISTS AND PHARMACEUTICAL STUDENTS. BY HENRY W. SCHIMPF, Ph.G. Professor of Inorganic Chemistry in Vie Brooklyn College of Pharmacy : Food Inspector of the Department of Health of the City of Brooklyn ; Member op the American Association for the Advancement of Science ; of the American Pharmaceutical Association ; of the Kings County Pharmaceutical Society ; of the Brooklyn Institute ; of the German Apothecaries Society of the City of New York ; Honorary Member of the Alumni Association of the Brooklyn College of Pharmacy, etc., etc. FI AS 7' EDITION. FIRST THOUSAND. NEWYORK; JOHN WILEY & SONS, 58 East Tenth Street. 1894. Copyright, 1894, BY Henry W. Schimpk. ROBERT DRUMMOND, ELECTROTYPER AND PRINTER, NEWYORK. PREFACE. This book is designed for the use of pharmacists, and especially as a text-book for students in pharmacy. In the first portion of the book the author has at- tempted, in explaining the principles of volumetric analysis, to combine thoroughness with simplicity of expression. The United States Pharmacopoeia has been taken as the basis of the work, and the volumetric processes therein given are followed throughout, each step being carefully explained, and chemical equations inserted, wherever deemed necessary. The author has also added descriptions of processes not given in the Pharmacopoeia, but which are worthy of consideration. In teaching volumetric analysis to students in phar- macy the author discovered the necessity for a work especially designed for this class of students. Moreover, the requirements of the new edition of the United States Pharmacopoeia, in which many volumet- ric processes are given, necessitate on the part of the careful pharmacist a knowledge of this branch of ana- lytical chemistry; and no work that has as yet fallen into the hands of the author has seemed to be exactly suited to the needs of the practical pharmacist. Con- sequently the necessity for a book based upon the Pharmacopoeia and free from technicality is apparent. IV PREFACE. The latter portion of the book is devoted to descrip- tions of such special analytical processes as the phar- macist may be called upon to use, and such as are taught in the pharmaceutical colleges. The author has selected such processes as can be easily and quickly executed, and has given the gravi- metric only where volumetric processes cannot be employed. In the subject-matter of the book little originality is claimed, but the author has used his own judgment in its selection and arrangement. He has endeavored in the text to give credit wher- ever it was due, and especially acknowledges his indebt- edness to the United States Pharmacopoeia; Sutton’s Volumetric Analysis ; Bartley’s, Simon’s, and Attfield’s text-books ; Blythe’s Food Analysis ; Prescott’s Organic Analysis ; Muter’s Analytical Chemistry (American editiori) ; Lefmann and Beam’s Milk and Water Analy- sis ; and Witthaus’ and Holland’s Urine Analysis. He wishes to express his thanks to Dr. J. F. Gold- ing for the valued assistance he has rendered during the preparation of the book. He is also indebted to Richards & Co., of 41 Barclay Street, N. Y. City, manufacturers of chemical apparatus, from whom sev- eral of the cuts were borrowed. The author submits this work to the consideration of pharmacists, trusting its reception will be at least commensurate with the labor expended in its prepa- ration. Henry W. Schimpf. 365 Franklin Aye., Brooklyn, N. Y. TABLE OF CONTENTS. Table of the Elements and their Atomic Weights . . xvii PAGE Abbreviations and Signs ........ xviii PART I, CHAPTER L Quantitative Analysis . . . ...... I The Gravimetric Method ........ I The Volumetiic Method . ..... 0 , I CHAPTER 11. Standard and Normal Solutions . 4 Normal Solutions ......... 4 Standard Solutions ......... 4 “ Standardized,” “ Set,” or “ Titrated ” Solutions ... 4 Decinormal Solutions ......... 8 Centinormal “ . .... . ... 8 Semi-normal ** 9 Double-normal “ ......... g Empirical “ 9 To “Titrate” .......... g Residual Titration 9 Indicator defined 10 CHAPTER 111. Litmus Tincture .......... 10 Phenolphthalein T. S. . ( 10 v VI TABLE OF CONTENTS. PAGE Methyl-Orange T. S. . , n Rosolic Acid T. S. . . . . . . . . , n Turmeric T. S. n Cochineal T. S Eosin T. S Brazil-wood T. S. . . . „ Fluorescein T. S. Potassium Chromate T. S, , . . , . . , . n Potassium Ferricyanide T. S n CHAPTER IV. General Principles . . . .12 Weights and Measures used in Volumetric Analysis. 15 CHAPTER V. Graduation of Instruments ........ 16 Table showing Expansion and Contraction of Liquids at Different Temperatures ......... 16 CHAPTER VI Apparatus used in Volumetric Analyses . . 17 The Burette . . . . . . . . . . .17 Mohr’s Burette 17 Glass-cock Burette . .17 Oblique-cock Burette . .... o ... 18 Mohr’s Foot Burette with Rubber Ball xq GayLussac’s Burette ..... .... 19 Bink’s Burette 19 Bead Stop ..... ...... 20 Burette Stand 25 Measuring-flask 20 Test-mixer Pipettes , . . . . . . . . . ,21 Single-volume Pipettes .21 Graduated Pipettes ......... 21 Bead Pipette 22 Nipple Pipette 22 Burette attached to Reservoir ....... 24 Table of contents. Use of Apparatus . . . .27 CHAPTER VII. PAGE Cleaning the Instruments . 27 Filling the Burette 27 Reading the Instruments ........ 28 Half-blackened Card ......... 29 Lrdman’s Float .......... 30 CHAPTER VIII. Calculating Results . . , .31 Rules for finding Percentage . 31 Factors or Coefficients ........ 33 Table of Approximate Normal Factors for Alkalies and Acids . 35 CHAPTER IX. Alkalimetry ........... 36 Analyses by Neutralization . .36 Preparation of Standard Oxalic-acid Solutions . . . -39 Preparation of Standard Sulphuric and Hydrochloric Acid Solutions . . . . . . . . . 40, 41 Estimation of A Ikaline Hydroxides ...... 43 Potassa ...... , .... 43 Liquor Potassa .......... 44 Soda ............ 45 Liquor Soda ...45 Aqua Ammonia .......... 46 “ “ Fortior 46 Spirit of Ammonia ......... 47 Estimation of Alkaline Carbonates ...... 47 Potassium Carbonate 48 Potassium Bicarbonate ........ 49 Sodium Carbonate . . . . . . . . .49 Sodium Bicarbonate ......... 50 Ammonium Carbonate . 51 Lithium Carbonate . . 51 Borax 54 Estimation of Organic Salts of the Alkalies . , . . .54 Potassium Tartrate ......... 55 Potassium and Sodium Tartrate . . . . . .57 TABLE OF CONTENTS. Potassium Bitartrate 58 PAGE Lithium Citrate 59 Potassium Citrate .... 0 .... 60 Potassium Acetate ......... 61 Sodium Acetate 62 Lithium Benzoate 63 Sodium Benzoate ... 64 Lithium Salicylate . 66 Sodium Salicylate ........ 67 fable showing Normal Factors for the Organic Salts of the Alkalies 68 Acidimetry ........... 68 Special Vessels for Preserving Alkali Solutions . . . , 6g Preparation of Normal Alkali Solutions ..... 69 Acetic Acid 73 “ “ Diluted 74 Glacial ......... 7b Vinegar . . . , . . . . . . . 74 Free Mineral Acids in Vinegar ....... 75 Citric Acid 76 Lime and Lemon Juice . 77 Hydrobromic Acid 77 Hydrochloric Acid ......... 78 Hypophosphorous Acid 79 Lactic Acid 80 Nitric Acid ... ........ 81 Phosphoric Acid . 82 “ “ Diluted . 82 “ “ Diluted 82 “ “ (Stolba’s Method) 82 Sulphuric Acid .......... 86 “ “ Aromatic 87 Tartaric Acid . . . . . . . . . -87 “ “ Diluted 87 Table showing Normal Factors, etc., for the Acids . . .88 Estimation of Alkaline Earths ....... 88 Preparation of Normal Sodium Carbonate V. S. . . . . 89 Liquor Calcis .......... 90 Calcium Carbonate ......... 91 “ Bromide ......... 92 TABLE OF CONTENTS. IX PAGE Calcium Chloride 93 Barium Chloride ......... 93 Strontium Lactate 94 “ Nitrate . . . . 93 CHAPTER X. Estimation of Haloid Salts ........ 97 Analysis by Precipitation . . . 96 Preparation of Decinormal Silver Nitrate V. S. . . . *97 Ammonium Bromide ......... 99 Lithium Bromide xoi Potassium Bromide . iox Sodium Bromide .......... 102 Strontium Bromide ......... 103 Calcium Bromide 103 Zinc Bromide .......... 104 Potassium lodide . 105 “ Personnel Method 106 Sodium lodide . 107 Strontium lodide ... 108 Zinc lodide 108 Ammonium Chloride 109 Potassium Chloride xog Sodium Chloride . . . . . . . . # .110 Zinc Chloride . . . . . . . . . .Ixo Syrup of Hydriodic Acid in ‘ “ Ferrous lodide ........ 112 “ “ Ferrous Bromide ........ 117 Saccharated Ferrous lodide 116 Preparation and Use of Standard Potassium Sulphocyanate V, S. (Volhard’s Solution) . ....... 113 Hydrocyanic Acid 117 Potassium Cyanide 120 Silver Nitrate 121 “ Fused 123 “ Diluted 123 “ Oxide 124 Liquor Plumbi Subacetatis ........ 124 7 showing Factors of Substances estimated by Precipitation. 125 X TABLE OF CONTENTS. CHAPTER XI. Oxidimetry 127 PAGE Estimation of Ferrous Salts . . . . . . . .128 Preparation of Standard Solution of 2KMn04 and . 129 Estimation of Ferrous Salts by KiCr-iOi , . . . .133 Saccharated Ferrous Carbonate . . , . . . .138 Ferrous Sulphate 140 Estimation of Ferrous Salts by . . . . .141 Ferrum Reductum ......... 143 Ferrous Sulphate ......... 145 Estimation of other Oxidizable Substances 145 Hypophosphorous Acid 146 Calcium Hypophosphite 148 Ferric Hypophosphite 149 Potassium Hypophosphite .150 Sodium Hypophosphite ........ 151 Hydrogen Peroxide . 152 Barium Dioxide . . . .157 Oxalic Acid ........... 158 Table of Substances which may be Estimated by Oxidation . 160 CHAPTER XII. Analysis by Indirect Oxidation . . .161 Preparation of Standard Solution of lodine . . . . .162 Arsenous Acid 163 Liquor Acidi Arsenosi, U. S. P. . . . . . . . 164 Liquor Potassa Arsenitis, U. S. P. . . . . . 165 Sulphurous Acid , . . .165 Sodium Sulphite .......... 166 Potassium Sulphite . .... 167 Sodium Bisulphite ... . ... 168 Sodium Thiosulphate ... ..... 168 Antimony and Potassium Tartrate 169 Table of Substances which may be Estimated by lodine . . .171 CHAPTER XIII. Estimation of Substances Readily Reduced . 172 Preparation of Standard Solution of Sodiu?n Thiosulphate . .173 Estimation of Free lodine ........ 175 TABLE OF CONTENTS. PAGE Liquor lodi Compositus 176 Tincture of lodine 177 Aqua Chlori 177 Calx Chlorata ...... ... 178 The Arsenous Acid Process 180 N Preparation of A rsenous-acid Solution . . . . . 181 10 Liquor Sodae Chloratae ........ 181 Estimation of Ferric Salts . . . . . . . .183 Ferric Chloride 184 Liquor and Tinctura Ferri Chloridi . . ... 185 Ferric Citrate 186 Liq. Ferri Citratis ......... 187 Ferri et Ammonii Citras 188 “ “ Potassii Tartras .188 Ferri Phosphas 188 “ “ Ammonii Tartras ........ 188 Ferri et Quininse Citras xBg Ferri et Strychninae Citras ........ 191 Ferri et Ammonii Sulphas ........ 192 Ferri Pyrophosphas . 194 Ferri Valerianas . 195 Liq. Ferri Acetatis 196 “ “ Nitratis 197 “ " Subsulphatis 198 “ “ Tersulphatis ........ 199 Hydrogen Peroxide, Estimation of, by Kingzett’s Method . . 200 N Table of Substances Estimated by Sodium Thiosulphate V. S. 201 PART 11. CHAPTER XIV. Collection of Sample 202 Sanitary Analysis of Water . . . 202 Color 203 Odor 203 Reaction . . 204 Suspended Matter 204 TABLE OF CONTENTS. PAGfi Total Solids • . , 204 Organic and Volatile Matter or Loss on Ignition , . . 205 Chlorine ........... 206 Ammonia .... ....... 207 Nessler’s Solution ...... „ 207 Albuminoid Ammonia ......... 210 Nitrates . . . , . . . . . . .211 Nitrites. . 214 Oxygen consuming Power ........ 216 Phosphates ...... 0 ... 217 Hardness, Temporary and Permanent ..... 219 Interpretation of Results ....... . 224 Estimation of CO2 in the Atmosphere . . 233 CHAPTER XV. Table showing Volume of .001 gm. of CO2 at various Temper- atures 237 Estimation of Alcohol in Tinctures and Beverages . 238 CHAPTER XVI. Table for Ascertaining the Percentages of Alcohol in Spirit from the Specific Gravity ....... 240 CHAPTER XVII. Estimation of Tannin .... 242 G. Fleury’s Method . 242 Lowenthal’s Method ......... 243 CHAPTER XVIII. Estimation of Oleic Acid . , . 246 CHAPTER XIX. Analysis of Soap .... 243 CHAPTER XX. Determination of the Melting-point of Fats . , 251 CHAPTER XXL Soxhlet Apparatus ... 253 Estimation of Oil or Fat in Emulsions and Ointments. 252 TABLE OF CONTENTS. CHAPTER XXII. Estimation of Starch in Cereals, etc. . .255 PAGE CHAPTER XXIII. Estimation of Sugars .... 259 Estimation of Glycerin . . „ .26 CHAPTER XXIV. CHAPTER XXV. Estimation of Phenol .... 266 Preparation of Standard Bromine Solution 266 By Koppeschaar’s Method 268 Dr. Waller’s Method . 272 Assay of Crude Carbolic Acid . 273 CHAPTER XXVI. Valuation of Pepsin, U. S. P. Method ..... 277 Pepsin 275 Bartley’s Method 278 Determination of the Diastasic Value of Malt and CHAPTER XXVII. Robert’s Method 281 Pancreatic Extracts .... 281 Park, Davis & Co.’s Method 283 CHAPTER XXVIII Table showing the Behavior of Some of the Alkaloids with Indicators 289 Volumetric Estimation of Alkaloids . . 285 Table showing Factor for Various Alkaloids when Titrating N with Acid V. S. 290 Estimation by Mayer’s Reagent 290 Alkaloidal Assay by Immiscible Solvents 292 Estimation of Alkaloidal Strength of Scale Salts. 295 CHAPTER XXIX. General Method for the Estimation of the Alkaloidal Strength of Extracts 295 XIV TABLE OF CONTENTS. PAGE Assay of Extract of Nux Vomica, U. S. P 296 “ “ Extract of Opium 298 “ “ Tincture of “ .... ... 300 “ “ Gum Opium ......... 301 “ “ Cinchona, U. S. P. . . . . . . . 302 “ “ FI. Extr. of Ipecac ...... 304 “ “ Ipecac Root ......... 306 Estimation of the Strength of Resinous Drugs .... 306 CHAPTER XXX. Estimation of Glucosides. . . . 308 CHAPTER XXXI Milk 309 Average Composition 309 Colostrum . . . . , . . . . . .310 Reaction 310 Specific Gravity ... ....... 310 Lactometer . . . . . . . . . . . 311 Table for Correcting the Sp. Gr. of Milk according to Tern Adulterations of Milk 313 perature . . . . . . . . . . 312 Total Solids and Water ........ 313 Fat, Adam’s Method 314 Werner-Schmidt Method 315 Calculation Method ......... 316 Calculation of Per Cent of Added Water . . . . .317 Total Proteids 318 Milk Sugar 318 CHAPTER XXXII. General Composition ......... 319 Butter 319 Reichert’s Process for the Detection of Foreign Fats . . . 319 Rapid Method for the Detection of Oleomargarine . . . 320 CHAPTER XXXIII. Urine 322 Reaction . ......... 322 TABLE OF CONTENTS. XV PAGE Composition 322 Specific Gravity 324 Total Solids 325 Chlorides ........... 326 Phosphates 327 Sulphates ........... 327 Total Acidity 328 Urea 329 Uric Acid ....... ... . 329 Abnormal Constituents . ....... 330 Albumen ........... 330 Blood 333 Pus 333 Sugar 334 Bile 33S Examination of Urinary Deposits 339 Analysis of Urinary Calculi 340 PART 111. Gasometrxc Analysis .... 342 CHAPTER XXXIV. Charles’ and Boyle’s Law ........ 344 The Nitrometer .... 342 CHAPTER XXXV. Assay of Amyl Nitrite 349 Assay of Spirit of Nitrous Ether . . 346 “ “ Sodium Nitrite ... 0 ... . 350 Estimation of Nitric Acid in Nitrates 350 Estimation of Soluble Carbonates . . 352 CHAPTER XXXVI. Estimation of Urea in Urine . , . .353 CHAPTER XXXVII. I. By Doremus’ Ureometer. 11. By the Gas-tube Method. 111. By Squibb’s Urea Apparatus ..... 353 TABLE OF CONTENTS. XVI CHAPTER XXXVIII. PAGE Hydrogen Dioxide . . . -357 Its Assay by the Nitrometer, and bySquibb s Urea Apparatus . 357 APPENDIX. Indicators 360 Reagents and Test Solutions 3^9 A LIST OF ELEMENTS OCCURRING IN VOLUMETRIC METHODS, THEIR SYMBOLS, AND ATOMIC WEIGHT! Name. Exact Atomic Weights according to Meyer and Seubert, adopted by the U. S. P. Approximate Atomic Weights. Albuminium A1 27.04 27.0 Antimony Sb 119.6 120.0 Arsenic As 74-9 75-o Barium Ba 136.9 136.9 Bismuth Bi 208.9 208.0 Boron B 10.9 11.0 Bromine Br 79.76 80.0 Cadmium Cd in.5 in.5 Calcium.... Ca 39-9r 40.0 Carbon C 11.97 12.0 Chlorine Cl 35-37 35-4 Chromium Cr 52.0 52-0 Copper. Cu 62.18 63.0 Gold Au 196.7 196.7 Hydrogen H 1.0 1.0 Iodine I 126.53 126 5 Iron Fe 55-88 56.0 Lead Pb 206.4 206.4 Lithium Li 7.01 7.0 Magnesium Mg 24-3 24.0 Manganese Mn 54-8 55-o Mercury Hg 199.8 200.0 Nitrogen N 14.01 14.0 Oxygen O 15.96 16.0 Phosphorus P 30.96 31.0 Platinum Pt 194-3 194-3 Potassium K 39-03 39-o Silver Ag 107.66 107.7 Sodium Na 23.0 23.0 Strontium Sr 87-3 87-3 Sulphur S 31.98 32.0 Tin Sn 118.8 118.0 Zinc Zn 65.x 65.0 ABBREVIATIONS AND SIGNS. Cc cubic centimetre. Gra gramme, 15.43235 grains. Gr grain. At.wt. . . . atomic weight. ■*' V. S volumetric solution. T. S test solution, according to U. S. P, U.S. P. . . . United States Pharmacopoeia. normal. 1 decinormal. 10 centinormal. 100 semi-normal. 2 2 or 2N . . double-normal. N * means that the figure is approximate. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Part I. IN TROD NOTION CHAPTER I. I. Quantitative Analysis is the determination of the proportions in which the constituents of a com- pound are present. The quantitative analysis of a substance may be made by the Gravimetric Method or by the Volumetric Method. 2. The Gravimetric Method consists in separating and weighing the constituents, either in their natural state or in the form of some new and definite com- pounds the composition of which is known to the oper- ator, and from their weights calculating the weights of the original constituents. For example: A silver solution is treated with by- 2 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. drochloric acid as long as a precipitate is produced. This precipitate is thoroughly washed, dried, and weighed. It consists of silver chloride 143.03 parts, which contain 107.66 parts (by weight) of metallic sil- ver. These operations are often very complicated, require great skill and elaborate apparatus, besides consuming considerable time. 3. The Volumetric Method is more easily per- formed. In this the quantity of the substance under examination is ascertained by a calculation based upon a measured quantity of a solution of known strength required to perform a certain reaction with it. For instance, if a silver solution is to be analyzed by this method, it is treated with a solution of sodium chloride of certain strength until no more silver chloride is pre- cipitated. The sodium-chloride solution used for this purpose N is a solution, and is made by dissolving one tenth of the molecular weight in grammes, in sufficient water to make one thousand cubic centimetres (1 litre). As seen by the equation, one molecule of sodium chloride (58.37 parts by weight) will precipitate all the silver out of one molecule of silver nitrate (169.55 parts by weight). AgN03 + NaCl = AgCl + NaN03 169-55 58.37 N Hence 1000 cc. of the sodium-chloride solution 10 represent 16.955 grammes of silver nitrate, and each cc. precipitates .016955 gramme. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 3 Volumetric operations can be quickly performed, and with great accuracy. The apparatus required is simple, and comparatively little skill is necessary. The volumetric method is therefore to be preferred to the gravimetric whenever it can be employed. The solutions used are known as volumetric or stan- dard solutions. 4 A TEXT-BOOK OE VOLUMETRIC ANALYSIS, CHAPTER 11. 4. Standard and Normal Solutions.—When volu- metric analysis first came into use the solutions were so made that each substance to be estimated had its own special volumetric solution, and this was generally of such strength as to give the result in percentages. Thus a certain strength of solution was used for testing soda, another for potassa, and a third for am- monia. These solutions were known as normal solutions, and since they are still to some extent in use it is im- portant that no misconception should exist as to what a normal solution is. It is to be regretted that some authors define a normal solution as one having the molecular weight in grammes of the active reagent in a litre. 5. A Normal Solution is one which contains in a litre a quantity of the active reagent, expressed in grammes, and chemically equivalent to one atom of hydrogen. 6. A Standard Solution is any solution employed in volumetric analysis for the purpose of estimating the strength of substances—that is, any solution the strength or chemical power of which has been deter- mined. It may be normal, decinormal, or of any strength so long as its strength is known. Such a so- lution is said to be “titrated ” (French titre title or power), sometimes called a “ set ” solution or “ stan- dardized ” solution. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 5 Standard solutions for use in volumetric analysis are usually solutions of acids, bases, or salts, and in two cases elements, namely, iodine and bromine. A standard solution of a base is usually used for the estimation of free acids. A standard solution of an acid is usually used for the estimation of a free base, or the basic part of a salt, the acid of which can be completely expelled by the acid used in the standard solution. Example, carbo- nates. A standard solution of a salt may be used, as a pre- cipitant, or it may be used as an oxidizing or reducing agent. That part of the reagent in a standard solution which reacts with the substance under analysis is the active constituent of the solution. As Ag in AgNOs is the active constituent of the standard solution of silver nitrate, AgNO, + NaCl = AgCl + NaNQ3, or Cl in NaCI, is the active constituent of the standard solution of sodium chloride. If the reagent is a base, as KOH, the basic part K is the active constituent. If the reagent is an acid, the active constituent is the acidulous part, as S04 in H2S04. If the action of the reagent is oxidizing, then that part of the reagent which produces the oxidation is the active constituent. The valence of an acid is shown by the number of replaceable hydrogen atoms it contains. Thus, HCI is univalent, H2S04 is bivalent; which means that a mole- cule of HCI is chemically equivalent to one atom of 6 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. hydrogen, and a molecule of H2S04 is chemically equivalent to two atoms of hydrogen. The valence of a base is shown by the number of hydroxyls it is combined with. As KOH is univalent, Ca(OH)2 is bivalent. The valence of a salt is shown by the equivalent of base which has replaced the hydrogen of the corre- sponding acid. Thus NaCl, in which Na has replaced H of HCI, is univalent. K2S04, in which K2 has replaced H2 of H2S04, is bivalent. If a normal solution is to be made for a special pur- pose, its reaction in that special case is to be consid- ered. As, when K2Cr207 is to be used as a precipitat- ing agent its reaction is as follows : 28a(C2H302)2 + K20207 + H2O = 2BaCr04 + 2KC2H302 + 2HC2H302. It is thus seen that one molecule of K2Cr207 will cause the precipitation of two atoms of barium in the form of chromate. Each atom of barium is chemically equivalent to two atoms of hydrogen; therefore one fourth of a molecule of K2Cr207 is equivalent to one atom of hydrogen. And therefore a normal solution of this salt when used as a precipitating agent must contain in one litre one fourth of its molecular weight in grammes. If K2Cr207 is to be used as an oxidizing agent, the three atoms of oxygen which it yields for oxidizing purposes must be taken into account. When this salt oxidizes it splits up into K2O -f- Cr203 -J- 03. The three atoms of oxygen combine with and oxidize the A TEXT-BOOK of volumetric analysis. salt acted upon, or they combine with an equivalent quantity of the hydrogen of an acid and liberate the acidulous part, which then combines with the salt. As the equations show, 6FeO + K2Cr207 = K2O + 0203 + 3Fe203; 6FeS04 + K.Cr.O, + ;H2SO4 = K2S04 + Cr2(S04)3 + 3Fe2(SO4)s; (7H.504 + K2Cr207 = 3H20 + 3504 + K2S04 + Cr2(S04)3). Each of these atoms of oxygen are equivalent to two atoms of hydrogen. Thus Oa is equivalent to H6. Hence a litre of a normal solution of K2Cr20,, when used as an oxidizing agent, contains one sixth of its molecular weight in grammes. The same may be said of potassium permanganate when used as an oxidizing agent. 2KMn04 has five atoms of oxygen which are avail- able for oxidizing purposes, and each of these is capa- ble of taking two atoms of hydrogen from an acid and liberating the acidulous part. The hydrogen equiva- lent of this salt may therefore be said to be one tenth of the weight of 2KMn04, and a normal solution of this salt contains 51.554 gm. in a litre. Sodium Thiosulphate (Hyposulphite), Na2S203, is another instance. The molecule of this salt has two atoms of sodium, which have replaced two atoms of hydrogen of thiosulphuric acid. Thus it would seem that a normal solution should contain one half of the molecular weight in grammes. But the particular re- action of this salt with iodine is taken into account. 8 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. One molecule reacts with one atom of iodine, as seen by the equation 2Na2S„03, 5HaO + I 2 = 2NaI + Na2S4Oc + ioH20. Since iodine is univalent, a molecule of the salt is equivalent to one atom of hydrogen. A normal solution of this salt therefore contains the molecular weight in grammes in a litre. / N\ According to the U. S. P., Normal solutions y—j are those which contain in one litre (1000 cc.) the mo- lecular weight of the active reagent in grammes, and reduced to the valence corresponding to one atom of replaceable hydrogen or its equivalent. Thus oxalic acid H2C204 -]-2H20 = 125.7, having two replaceable H atoms. One half of its molecular weight in grammes is contained in a litre of its normal solution, while hydrochloric acid HCI = 36.37, which has but one replaceable H atom, has its full molecular weight in grammes in a litre of its normal solution. Sulphuric acid H2S04 has two replaceable H atoms, so its normal solution contains one half of its molecu- lar weight in grammes in a litre. NaOH and KOH being monobasic, a litre of a normal solution of either contains the full molecular weight of the salt in grammes. N 7. Decinormal Solutions, —, are one tenth the ‘ 10 strength of normal solutions. N 8. Centinormal Solutions, , are one hundredth 100 the strength of normal solutions. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 9 N 0. Seminormal Solutions, —, are one half the 2 strength of normal solutions. 2 io. Double-normal Solutions, -rr, are twice the ’ N strength of the normal. 11. Empirical Solutions are those which do not contain an exact atomic proportion of reagent, but are generally of such strength that I cc. = o.oi gm. of the substance upon which it acts. 12. To Titrate a substance means to test it volu- metrically for the amount of pure substance it con- tains. The term is used in preference to “tested” or “ analyzed,” because these terms may relate to quali- tative examinations as well as quantitative, whereas ti- tration applies only to volumetric analysis. 13. Residual Titration, Re-titration, sometimes called Back Titration, consists in treating the substance under examination with standard solution in a quan- tity known to be in excess of that actually required ; the excess (or residue) is then ascertained by residual titration with another standard solution. . Thus the quantity of the first solution which went into combination is found. Example.—Ammonium carbonate is treated first with N tH.S04 in excess, and the excess then found by ti- tration with KOH. 1 N The quantity of the —KOH used is then deducted from the quantity of HaS04 added, which gives the quantity of the latter which was neutralized by the ammonium carbonate. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER 111. An Indicator is a substance which is used in volu- metric analysis, and which indicates by change of color, or some other visible effect, the exact point at which a given reaction is complete. Generally the indicator is added to the substance under examination, but in a few cases it is used along- side, a drop of the substance being occasionally brought in contact with a drop of the indicator. Thus in estimating an alkali with an acid-volumetric solution the alkali is shown to be completely neutral- ized when the litmus tincture which was added becomes faintly red or the phenolphthalein colorless. Again, when haloid salts are estimated with nitrate-of-silver solution, chromate of potassium is added as indicator. A white precipitate is produced as long as any halogen is present to combine with the silver, and when all is precipitated the chromate of potassium acts upon the silver nitrate, forming the red-silver chromate, this color thus showing that all the halogen has been pre- cipitated. INDICATORS. The principal indicators used are ; Tincture of Litmus, which shows acidity by turn- ing red and alkalinity by becoming blue. Phenolphthalein Solution, which is colorless in acid solutions and red in alkaline solutions, but is not A TEXT-BOOK OF VOLUMETRIC ANALYSIS. reliable for alkaline phosphates, bicarbonates, or am- monia. Methyl-orange Solution turns red with acids and yellow with alkalies. It is not affected by carbonic acid, and is therefore adapted for the titration of alka- line carbonates. Rosolic-acid Solution is yellow with acids and vio- let-red with alkalies. It is very sensitive to ammonia. Tincture of Turmeric turns brown with alkalies, and the yellow color is restored by acids. Cochineal Solution turns violet with alkalies and yellowish with acids. It is used chiefly in the presence of ammonia or alkaline earths. Eosin Solution is red by transmitted light, and shows a strong green fluorescence by reflected light. Acids destroy this fluorescence and alkalies restore it. Brazilwood Test-solution turns purplish red with alkalies and yellow with acids. Fluorescein Test-solution shows a strong green fluorescence by reflected light in the presence of the least excess of an alkali. used in the titration of haloid salts with silver-nitrate solution. It indicates that all the halogen has com- bined with the silver by producing a red-colored pre- cipitate (silver chromate). Neutral Potassium-chromate Test-solution is Potassiume-ferricyanide Test-solution is used in the estimation of ferrous salts with potassium-dichro- mate solution. It gives a blue color to a drop of the solution on a white slab as long as any iron salt is present which has not been oxidized to ferric. Many other indicators are also used. 12 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER IV. GENERAL PRINCIPLES OF CHEMICAL COM BINATION UPON WHICH VOLUMETRIC ANALYSIS IS BASED. I. When substances unite chemically the union always takes place in definite and invariable proportions. Thus when silver nitrate and sodium chloride are brought together, 169.55 parts (by weight) of silver ni- trate and 58.37 parts (by weight) of sodium chloride will react with each other, producing 143.05 parts of a curdy white precipitate (silver chloride). These substances will react with each other in these proportions only. If a greater proportion of silver nitrate than that above stated be added to the sodium chloride, only the above proportion will react, the excess remaining unchanged. The same is true if sodium chloride be added in excess of the above proportions. For instance, if 200 parts of silver nitrate be mixed with 58.37 parts of sodium chloride 169.55 parts only will react with the sodium chloride, while 30.45 parts of silver nitrate will remain unchanged. Again, when potassium hydroxide and sulphuric acid are mixed potassium sulphate is formed, 111.98 parts of potassium hydroxide and 97.82 parts of sulphuric acid being required for complete neutralization. These two substances unite chemically in these proportions only. A TEXT-BOOK OF VOLUMETRIC ANALYSTS. 13 The equation is 2KOH + H2S04 = K2S04 + 2H20. m.98 97.82 In other words, 111.98 parts of KOH will neutralize 97.82 parts of H2S04, and consequently 97.82 parts of H2S04 will neutralize 111.98 parts of KOH. Oxalic acid and sodium carbonate react upon each other in the proportions shown in the equation H2CA • 2H20 + Na2CO, = Na2C204 + C02 + 3H20 125.7 105.85 125.7 parts of crystallized oxalic acid are neutralized by 105.85 parts of anhydrous sodium carbonate. 2. Definite chemical compounds always contain the same elements in exactly the same proportions, the proportions being those of their atomic weights, or some multiple of these weights. Thus sodium chloride (NaCl) contains 23 parts of metallic sodium and 35.37 parts of chlorine, these be- ing the atomic weights of sodium and chlorine, respec- tively. Potassium sulphate (K2SO4) contains twice 39.03 = 78.06 parts of potassium, 31.98 parts of sulphur, and four times 15.96 = 63.84 parts of oxygen. Potassium hydroxide (KOH) contains 39.03 parts of potassium, 15.96 parts of oxygen, and one part of hy- drogen. Hydrochloric acid (HCI) contains one part of hydrogen and 35.37 parts of chlorine. Upon these facts the volumetric methods of analysis are based. It has been shown that 97.82 grammes of sulphuric acid will neutralize 111.98 grammes of potassium hy- 14 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. dioxide ; it is therefore evident that if a solution of sul- phuric acid be made containing 48.91 grammes of the pure acid in 1000 cc. that one cc. of this solution will neutralize 0.056 gm. of potassium hydroxide. In esti- mating alkalies with this acid solution the latter is added from a burette, in small portions, until the alkali is neutralized, as shown by its reaction with some indi- cator. Each cc. of the acid solution required before neutra- lization is complete indicates 0.056 gm. of KOH, and the number of cc. used multiplied by 0.056 gm. gives the quantity of pure KOH in the sample analyzed. One cc. of the same solution will neutralize 0.03996 gm. of sodium hydroxide (NaOH), 0.052925 gm. of anhydrous sodium carbonate (Na2COs), etc. If a solution of crystallized oxalic acid be made by dissolving 62.85 gm- in sufficient water to make 1000 cc., we will have a normal solution, the neutralizing power of which is exactly equivalent to the above-mentioned normal sulphuric-acid solution. The strength of acids is estimated by alkali volumet- ric solutions. A normal solution of potassium hydrox- ide containing 55.99 gm. in the litre will neutralize exactly 1 litre of the normal acid solution ; 1 cc. of this normal alkali will neutralize 0.03637 gm. of HCi, 0.06285 gm. of H2C204, or 0.04891 gm. of H2S04, etc. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 15 CHAPTER V. WEIGHTS AND MEASURES USED IN VOLUMETRIC ANALYSIS. The metric or decimal system is used in this country and on the continent in Europe, but in England the grain system is used. The unit of weight in the metric system is the gramme (gm.). A gramme of distilled water at its maximum density, 4° C. (390 F.), measures one cubic centimetre (cc.). A kilogram is 1000 gms. A litre is 1000 cubic centimetres. Volumetric instruments are graduated in the metric system, but not at 40 C. If they were, it would neces- sitate the carrying out of all volumetric operations at that temperature, and it would be impossible to do careful volumetric work except for two or three months of the year, unless troublesome calculations for the cor- rection of volume were made. For this reason the temperature of 15° C. (590 F.) was taken as the standard, and at this temperature most volumetric instruments are graduated. In making very careful examinations the work should be done at this temperature. One gramme of distilled water at I5°C. measures one cc. as used in volumetric analysis. The true cc, weighs at 150 C. only 0.999 gm- Casa- major (C. N., xxxv. 160) gives the following figures, 16 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. showing the relative contraction and expansion of water below and above 150 C. Degree C. Degree C. 8 .000590 17 + .000305 9 .000550 18 + .000473 10 .000492 19 -j- .000652 11 .000420 20 -f- .000841 12 .000334 21 -|- .001039 13 .000236 22 -j- .001246 14 .000124 23 -f- .001462 15 normal 24 -|- .001686 16 -j- .000147 25 + .001919 By means of these numbers it is easy to calculate the volume of liquid at 150 C. corresponding to any volume observed at any temperature between 8° C. and 250 C. If 25 cc. of solution had been used at 20° C., the table shows that 1 cc. of water passing from 150 to 20° is increased to 1.000841 cc. Therefore, by dividing 25 cc. by 1.000841, the quotient, 24.97 cc., is obtained, which represents the volume at 150 C. corresponding to 25 cc. at 200 C. These corrections are of value only for very dilute solutions and for water, but useless for concentrated solutions. Slight variations of atmospheric pressure may be disregarded. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER VT. APPARATUS USED IN VOLUMETRIC ANALYSES. The Burette is a graduated glass tube which holds from 25 to 100 cc. and is graduated in fifths or tenths of a cc., and provided at the lower end with a rubber tube and pinch - cock. The use of this instrument is to accu- rately measure quantities of standard solutions used in an analysis. It is in an upright position when in use, and the flow of the solution can be regu- lated so as to run out in a stream or flow in drops by pressing the pinch- cock between the thumb and forefinger. The quantity of solution used can be read from the graduation on the out- side of the tube. This is the simplest and most common form of burette, and is known as Mohrs (Fig. 1). The greatest drawback to this burette is that it cannot be used for permanganate or other solutions that act upon the rubber. Fig. i. This defect can be overcome by the use of a burette having a glass stop-cock in place of the rubber tubing and pinch-cock. This form has the additional advan- tage of being capable of delivering the solution in 18 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. drops while both hands of the operator are disen- gaged (Fig. 2). Another good arrangement is that in which the tap Fig. 2. Fig. 3. Fig. 4. is placed in an oblique position, so that it will not easily drop out of place (Fig. 3). These glass stop-cock burettes should be emptied and washed immediately after use, especially if soda or potassa solution has been used ; for these act upon the glass, and often cause the stopper to stick so firmly that it cannot be turned or removed without danger of breaking the instrument. Other forms of burettes are Mohr's Foot Burette, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 19 with rubber ball (Fig. 4). There is a hole in the rubber ball, and by placing the thumb over the hole and gently squeezing, the flow of the liquid may be nicely regulated Sink's Biirettc (Fig. 5) is used by holding in the Fig. 6. tfiG 6a. hand and inclining sufficiently to allow the liquid to flow, then placing in an upright position, and reading when the surface of the liquid has settled. Fig. 5. Gay-Lussac s (Fig. 6) must also be inclined when used. A wooden foot is generally provided, into 20 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. which this burette is placed to rest in an upright position. By inserting a tightly-fitting cork into the open end and passing through this cork a small bent glass tube, the flow of the solution from the exit-tube can be nicely regulated by blowing through the small glass tube. The necessity for inclining the burette is thus obviated. See Fig. 6a. These two latter burettes being held in the hand when in use, there is a chance of increasing the bulk of the fluid by the heat of the body, thus leading to incorrect measurements. The use of the pinch-cock in Mohr’s burette may be dispensed with by introducing into the rubber tube a small piece of glass rod, which must not fit too tightly. By firmly squeezing the rubber tube sur- rounding the glass rod a small canal is opened, through which the liquid es. Closed Open Fig. 7. capes. A very delicate action can in this way be obtained, and the flow of the liquid is completely under the control of the operator. (See Fig. 7.) The Measuring-flask is a vessel made of thin glass having a narrow neck, and so constructed as to hold a definite amount of liquid when filled up to the mark on the neck. These flasks are of various sizes, holding 100, 250, 500, 1000 cc., etc., but are generally called “Litre Flasks.” (Fig. 8). They are used for making volumetric solutions. Those which have the mark below the middle of the neck are to be preferred, because the contents can be more easily shaken. for measuring and mixing smaller quantities of solutions. The Test Mixer, or Graduated Cylinder (Fig. 9), is A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 21 They are made of different sizes, holding 100, 250, 500, and 1000 cc., and graduated in fifths or tenths of a cc. Pipettes are of two kinds: those which are marked for one quantity only, and those which are graduated on the stem to deliver various quantities (Fig. 10 and Fig. 10a). Pipettes are filled by applying the mouth to the upper end and sucking the liquid up to the mark; then by placing the moistened forefinger over the upper opening the liquid is prevented from run- ning out, but may be delivered in drops or allowed to run out to any mark by loosening the finger. Fig. 8. Fig. 9. A very convenient form of pipette is one which has attached to its upper end a piece of rubber tubing, into which a piece of glass rod has been inserted. 22 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. By squeezing the rubber surrounding the glass rod firmly between the fingers a canal is opened, and the liquid can be drawn up into the pipette by suction with the lips. Then by gentle pressure the liquid can be allowed to run out slowly, and stopped at any point by removing the pressure (Fig. n). The Nipple Pipette is very convenient for measur- Fig. io. Fig. ioa. Fig. ii. Fig. 12. ing small quantities of liquids, such as I or 2 cc. (Fig. 12). When a volatile or highly poisonous solution is to be measured it is not advisable to suck it up with the mouth. The pipette may then be filled by dipping it A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 23 into the liquid contained in a long, narrow vessel until the liquid reaches the proper mark on the pipette, then closing the upper opening and withdrawing. When this is done the liquid which adheres to the outside of the pipette should be dried off before the measured liquid is delivered. Fig. 13. 24 a TEXT-BOOK OF VOLUMETRIC ANALYSIS. When a number of estimations are to be made in which the same volumetric solution is employed, the arrangement shown in Figs. 13 and 14 is very ser- viceable. A T-shaped glass tube is inserted between the lower end of the burette and the pinch-cock and connected by a rubber tube with a reservoir containing the volu- metric solution. The tube which communicates with the reservoir is provided with a pinch-cock, which when open allows the solution to flow into and fill the burette in so gradual a manner that no bubbles are formed. The burette is emptied in the usual manner. Fig. 14. If the titration is to be conducted at a high temper- ature, as in the estimation of carbonates, when litmus is used as the indicator, or in the estimation of sugar A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 25 by copper solution, a long rubber tube should be attached to the lower end of the burette. The boiling can then be done at a little distance, and the expansion Fig. 15. of the liquid in the burette avoided. The pinch-cock is fixed about midway on the tube. Fig. 16. The burette support represented in Fig. 15, with heavy tripod base, is one of the best for one or two 26 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. burettes. It stands firmly upon an uneven surface, and does not easily tip over. If two burettes are to be supported the clamp shown in Fig. 16 may be used. Fig. 17 represents a revolving burette-holder for eight burettes. Fig. 17. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 2 7 CHAPTER VII. ON THE USE OF APPARATUS. It is important that all apparatus used in volumetric analysis should be perfectly clean. Even new appara- tus should be cleansed by passing dilute hydrochloric acid through them and then rinsing with distilled water. If the burette, pipette, or other instrument is even slightly greasy, the liquid will not flow smoothly, and drops of the liquid will remain adhering to the sides, thus leading to inaccurate results. Greasiness may be removed with dilute soda solution. If this fails the instrument should be allowed to remain for some little time in a solution containing sulphuric acid and potassium dichromate, which will radically remove all traces of grease. The burette or other measuring instruments should never be filled with volumetric solution without first rinsing, even if the burette be perfectly dry. It is well to wash the inside of the instrument with two or three small portions of the solution with which it is to be filled. The burette may be filled with the aid of a funnel, the stem of which should be placed against the inner wall of the burette so that the solution will flow down the side and thus prevent the formation of bubbles. The burette should be filled to above the zero mark, 28 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. and the air-bubbles, if there are any, removed by gently tapping with the finger. A portion of the liquid should then be allowed to run out in a stream so that no air-bubbles remain in the lower part of the burette. In the glass tap burette it can be easily seen if any air is present, but in the pinch-cock burette it is sometimes necessary to take hold of the rubber tube between the thumb and fore- finger and gently stroke upward. Or the glass nip at the lower end of the burette may be pointed upward, and the pinch-cock opened wide so that a stream of the liquid will pass through and force out any air that may be inclosed. ON THE READING OF INSTRUMENTS. In narrow vessels the surfaces of liquids are never level. This is owing to the capillary attrac- tion exerted by the sides of the vessel upon the liquid, drawing the edge up and forming a saucerlike concavity (Fig. 18). All liquids present this concave surface except mercury, the surface of which is convex. This behavior of liquids makes it difficult to find a distinct level, and in reading the measure either the upper meniscus {a) or the lower meniscus {&) may be used (Fig. 19). Fig. 18. The most satisfactory results are obtained if the low- est point of the curve {b) is used, especially with light- colored solutions. But if dark-colored or opaque solu- tions are measured, it is necessary to use the upper meniscus (a) for reading. In all cases the eye should be brought on a level A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 29 with the surface of the liquid in reading the gradua- tion. The eye is very much assisted by using a small card, the lower half of which is black and the upper half white. This card is held behind the burette, the dividing line between white and black being about an eighth of an inch below the surface of the liquid. The Fig. 19. Fig 20. Fig. 21. eye is then brought on a level with it, and the lower meniscus can be distinctly seen as a sharply-defined black line against the white background (Fig. 20). Erdman’s Float, Fig. 21, is an elongated glass bulb, which is weighted at its lower end with mercury, to keep it in an upright position when floating. It is of such diameter that it will slide easily up and down A TEXT-BOOK OF VOLUMETRIC ANALYSIS. inside of a burette. There is a ring at the top by which it can be lifted in or out by means of a bent wire. Around its centre a line is marked. At this line instead of at the meniscus the reading is taken. These floats are sometimes provided with a thermo- meter, and they then register the temperature as well as the volume. Litre flasks are sometimes made with two marks on the neck very near together; the lower one is the litre-mark. If the flask is required to deliver a litre, it must be filled to the upper mark ; the difference be- tween the two measures being the equivalent of the liquid which remains in the flask, adhering to the sides. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 31 CHAPTER VIII. METHODS OF CALCULATING RESULTS. N Each cc. of a— umvalent volumetric solution con- I tains yoVo °f the molecular weight in grammes of its reagent, and will neutralize TqVo °f the molecular weight of a univalent substance, or °f the molec- ular weight of a bivalent substance. N Each cc. of a— bivalent volumetric solution contains i Wro °f the molecular weight in grammes of its reagent, and will neutralize or combine with -j-gVo- of the molec- ular weight of a bivalent salt, or y-gVo °f the molec- ular weight of a univalent salt. N A —is only tl the strength of a normal solution and will neutralize only yC- the quantity of salt, etc. Normal and decinormal solutions of acids should neutralize normal and decinormal solutions of alkalis, volume for volume. Decinormal solution of silver ni- trate and decinormal solution of hydrochloric acid or sodium chloride should combine volume for volume, etc. The Rules for Obtaining the Percentage of pure substance in any commercial article, such as acids, ah kalis, and various salts, are; 32 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. I. With normal solutions -Tj- or (according to its atomicity) of the molecular weight in grammes of the substance is weighed for titration, and the number of cc. of the V. S. required to produce the desired reaction is the percentage of the substance whose molecular weight has been used. Thus, if sodium hydroxide (NaOH) is to be exam- ined by titration with a normal acid solution yL- of its molecular weight in grammes, 4 gms. is weighed out, and each cc. of the acid solution required represents lie of the pure salt. If sodium carbonate (Na2CO3) is to be tritated Gf its molecular weight in grammes, 5.3 gms. is taken. 2. With decinormal solutions yL or of the mo- lecular weight in grammes of the substance to be ana- lyzed is taken, and the number of cc. will, in like man- ner, give the percentage. The following equations will serve to explain more fully: N Sodium hydroxide with sulphuric acid: 2NaOH + H2S04 = Na2S04 + 2H20. 2 X 40 = 80 2)gB 10)40 49 = to 'ooo cc. 4-0 gms = to 100 cc. Sodium carbonate zvith sulphuric acid: Na2C03 + H2S04 = Na2S04 + H2O + C02. 2)gB 20)106 49 to 1000 cc. 5.3 gms. = to ioq cc, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 33 N With sulphuric acid: io 2NaOH + H2S04 = Na2S04 + 2HaO. 2X40 = 80 2)98 100) 40 49 =to 1000 CC. 0.40 gins. =to too cc. 3. Factors or coefficients for calculating the analy- ses.—\t frequently occurs that from the nature of the substance, or from its being in solution, this percentage method cannot be conveniently followed. The best way to proceed in such a case is to find the factor. The first step in all cases is to write the equation for the reaction which takes place between the sub- stance under analysis and the solution used. For instance, a solution of caustic potash is to be N examined, a solution of sulphuric acid being used. 2KOH + H2S04 = K2S04 + 2H20. 2)112 2)98 N 56 49 =to 1000 cc. acid. N ... 0.56 gm. .049 =to 1 cc. acid. N The factor for KOH when solution is used is 1 .056 gm., that being the quantity neutralized by each cc. of the acid. If acid were used the factor 1 10 would be .0056 gm. The number of cc. of the acid used to produce the desired result, when multiplied by the factor gives the quantity in grammes of KOH in the solution taken. 34 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Example.—lf 10 grammes of caustic-potash solu- N tion were taken, and 40 cc, of —• acid were required, the logms. of solution contained .056 gm. X 40 = 2.24 gms. of pure KOH. To find the percentage, the following formula may be used. Q X ioo —w~ =*• Q = the quantity of pure substance found by calcula- tion; W weight of substance taken. If the above example is taken, we have 2,24 X 100 —— = 22.45. 10 Or the calculation may be made by proportion. The quantity of the substance taken is always the first term, and the quantity of pure substance found, the second term. The following rule is easily remembered : As the quantity taken is to the quantity found, so is 100 to x, the percentage of pure substance in the sample. Three terms of the equation being given, the fourth is found by multiplying the means and dividing the product by the given extreme. By applying this rule to the above case we have io : 2.24 :: 100 •x' x 22.43 106 0-053 Sodium bicarbonate NaHCOs 84 0.084 Potassium hydroxide KOH 56 0.056 Potassium carbonate k2co3 138 0.069 Potassium bicarbonate khco3 100 0. too Ammonia (gas) nh3 17 0.017 Ammonium carbonate, normal. ... (nh4)2co3 96 0.048 Ammonium carbonate, commercial.. n3h„ca 157 0.0^2^- Lime CaO 56 0.028 Calcium hydroxide Ca(OH)2 74 0.037 Calcium carbonate CaC03 too 0.050 Nitric acid HN03 63 O.063 Hydrochloric acid HC1 36-4 O.O364 Sulphuric acid h2so4 98 O.O49 Oxalic acid, crystallized H2C204.2H30 126 O.063 Acetic acid hc2h3o2 60 0.060 * This is the coefficient by which the number of cc. of normal solu- tion used is to be multiplied in order to obtain the quantity of pure substance present in the material examined. 36 A TEXT-BOOK UE VOLUMETRIC ANALYSIS, CHAPTER IX. ANALYSIS BY NEUTRALIZATION. This is based upon the fact that acids are neutralized by alkalies and alkalies by acids. The strength of an acid is estimated by the quantity of alkali that is required to neutralize it. This process is called acidimetry. The strength of an alkali is found by the quantity of an acid that is required to neutralize it. This process is called alkalimetry. The stronger the acid, the more alkali is required, and vice versa. A substance is said to be alkaline when it turns red litmus blue; phenolphthalein, red; turmeric, brown; etc. Acid, when it turns blue litmus red ; red phenol- phthalein, colorless, etc. The principal alkaline substances are the hydroxides and carbonates of sodium, potassium, and ammonium, and the hydroxides and oxides of calcium, barium, and strontium, and the alkaloids. When an acid is brought in contact with an alkali combination takes place, and a neutral salt is formed. This combination takes place in definite and invariable proportions ; thus ; If 112 parts of potassium hydroxide are mixed with 98 parts of absolute sulphuric acid the alkali as well as the acid will be neutralized. If only 80 parts of the acid have been added the mixture would still be alkaline, for it requires 98 parts of the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 37 add to neutralize it. If more than 98 of the acid have been added the mixture would consist of potassium sulphate and free sulphuric acid. The reaction is thus illustrated ; 2KOH + H2S04 = KsS04 + 2H20. XT 17Q U o Potassium 2 sulphate. 02 = 32 S = 32 u, = 2 04 =64 I 12 98 Sodium hydroxide will unite with oxalic, and form a neutral compound in the proportion of 80 parts by weight of the former and 126 parts by weight of the latter, as the equation shows ; 2NaOH + H2C204.2H20 = Na2Q04 + 4HaO. 2Na =46 6H = 6 2O =32 2C =24 211 = 2 60 =96 8o 126 NH4OH + HCI = NH4CI + h2o. N= 14 H = 1. 5H = 5 Cl = 35-4 O = 16 35 36-4 Ammonium Hydrochloric hydroxide. acid. Na2C03 + 2HCI = 2NaCI + H2O + C02. 106 72.8 Sodium carbonate. 38 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Upon a careful perusal of the foregoing equations it will be seen that since definite weights of acids neu- tralize definite weights of alkalies the quantity of a certain alkali in solution can be easily determined by the quantity of an acid solution of known strength re- quired to neutralize it, and vice versa. If we make a solution of oxalic acid of such strength that 1000 cc. of it contains 63 gms. of the crystallized acid, 1 cc. of it will neutralize .056 gm. of KOH, .040 gm. of NaOH, or .035 gm. of NH4OH. Thus if 10 gms. of solution of KOH be treated with this oxalic-acid solution and it is found that 25 cc. of it are required to neutralize the alkali, the alkali solution contains 25 x -056 = 1.4 gms. of pure KOH. Since the acid and alkali as well as the neutral salt " hich is formed are colorless, and no visible change takes place during the reaction, it is necessary to add some substance which by change of color will show when the neutralization is complete. Such substances are known as indicators. ' A number of these are spoken of on page 10. Neutralization is sometimes called saturation. ALKALIMETRY. possible to carry out the titration of most alkalies with only one standard acid solution, but the standard acids are frequently required in other processes besides mere saturation, and it is therefore advisable to have a variety. Preparation of Acid Volumetric Solutions.—It is The standard oxalic acid is preferred by some be- cause of the ease with which it may be prepared, pro- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 39 vided a pure acid can be had. It does not, however, keep very long, and when used for titrating carbonates with methyl orange as an indicator the end reaction is not very distinct. Oxalic acid cannot very well be used for the titration of alkaline earths, since it forms insoluble compounds with these metals. Sulphuric acid V. S. is preferred by others. A pure acid can be gotten without difficulty, and the standard solution made with it is totally unaffected by boiling, which cannot be said of either nitric or hydrochloric acid. Sulphuric acid, however, forms with alkaline earths insoluble compounds. For this reason standard solution of hydrochloric acid must frequently be em- ployed. Normal Oxalic Acid V. S., U. S. P.—H2C204-[- 2H20 = 125.7. | §ms- in 1 tre Dissolve 62.85 gms. (*63 gms.) of pure oxalic acid (see below) in enough water to make, at or near 150 C., exactly 1000 cc. Pure oxalic acid, crystallized, is in the form of colorless, transparent, clinorhombic crystals, which should leave no residue when ignited upon platinum foil. It is completely soluble in 14 parts of water at l's° C. If the acid leaves a residue on ignition it should be purified by recrystallization, as directed by the U. S. P. N 1 cc. of oxalic acid V. S. is the equivalent of— NaOH 0.03996 gm. KOH 0.05599 “ NH3 0.01701 “ 40 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Decinormal Oxalic Acid V. S., U. S. P.—H2C204 + 2H20 = 125.7. } gms* in 1 litre* Dissolve 6.285 gms- (*6.3 gins.) of pure oxalic acid in enough water to make, at or near 150 C., exactly 1000 cc. N 1 cc. of oxalic acid V. S. is the equivalent of— -10 NHa 0.001701 gm. KOH 0.005599 NaOH 0.003996 “ Normal Hydrochloric Acid V, S., U. S. P.— HCI = 36.37, | gms< in 1 litre. Mix 130 cc. of hydrochloric acid of sp. gr. 1.163, with enough water to measure, at or near 150 C., 1000 cc. Of this liquid (which is still too concentrated) meas- ure carefully into a flask 10 cc., add a few drops of phenolphthalein T. S., and gradually add from a burette potassium hydroxide V. S. until a permanent pale N pink tint is produced. Note the number of cc. of potassium-hydroxide solution consumed, and then dilute the acid so that equal volumes of this and the N KOH V. S. neutralize each other. 1 Example.—Assuming that the 10 cc. of the acid N solution required 12 cc. of the KOH, each 10 cc. of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. tlie acid must be diluted to 12 cc., or the whole of the remaining acid in the same proportion. After the dilution a new trial should be made. 10 cc. of the acid V. S. should require exactly 10 cc. of the alkali. This solution is exactly equivalent in neutralizing N power to oxalic acid V.S. Normal Sulphuric Acid V. S., U. S. P.—H2S04 = 97-82- *4991 | gms- in 1 litre- Mix carefully 30 cc. of pure concentrated sulphuric acid (sp. gr. 1.835) with enough water to make about 1050 cc., and allow the liquid to cool to about 150 C. Titrate 10 cc. of this liquid in the manner described N under hydrochloric acid, and dilute it so that equal volumes of the acid and the alkali will neutralize each other. Note.—lt is recommended in the U. S. P. that when a normal acid solution is required the normal sul- N phuric acid should be employed in place of oxalic. The oxalic-acid solution has a tendency to crystallize on the point of the burette. Decinormal Sulphuric Acid V. S., U. S. P.— 1I2S04 = 97.82. 91 | gms- in a litre. Dilute 10 cc. of the normal sulphuric-acid solution with enough water to make too cc. The standardization of normal acid solutions may 42 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. also be effected by the use of pure anhydrous sodium carbonate. Pure anhydrous sodium carbonate may be obtained by heating to dull redness a few grammes of pure sodium bicarbonate for about 15 minutes. The result- ing carbonate is practically free from impurity. The sodium bicarbonate loses on ignition one half of its carbonic acid gas: 2NaHC03 + Heat = Na2C03 + C02 + H2O. The bicarbonate should, however, be tested before igniting, and if more than traces of chloride, sulphate, or thiosulphate are found, these may be removed by washing a few hundred grammes, first with a saturated solution of sodium bicarbonate, and afterward with distilled water. °. 53 gm. of the pure anhydrous sodium carbonate is accurately weighed and dissolved in about 20 cc. of water in a flask and a few drops of methyl orange T. S. added as indicator. The acid to be “set” or “stan- dardized ” is then run into the sodium-carbonate solu- tion until a permanent light-red color is produced. It N should require exactly 10 cc. of the -y acid solution. If 8 cc. of the acid solution are consumed to bring about the required result, then every 8 cc. must be diluted to 10 cc., or the whole of the remaining solu- tion must be diluted in this proportion : Na2C03 + H2S04 = Na2S04 + H2O + C02. 2)106 2)98 53 gms. 49 =to 1000 cc. —V. S.; 0.53 g,n- =to 10 cc. 1 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 43 Instead of methyl orange, litmus tincture may be used. The carbonic-acid gas which is liberated in this reaction turns litmus red; the contents of the flask should therefore be boiled for a few minutes to drive off the C02, when the blue color will return. More acid is then run in until the mixture after boiling remains of a neutral color; indicating that just enough acid has been added to complete the reaction expressed in the foregoing equation. ESTIMATION OF ALKALINE HYDROXIDES. A definite quantity of the substance is taken (gen- erally weighed), and diluted with or dissolved in a little water in a flask or beaker. A few drops of a suitable indicator are now added, and the standard acid solution allowed to flow in until the last drop added just causes the color to change, the flask being agitated after each addition of the acid solution. Potassa. KOH = U. S. P.—Weigh carefully i gm. of potassa, dissolve it in a small quantity of water, add a drop of phenolphtalein solution as indi- N cator, and titrate with sulphuric acid V. S. until the red color just disappears. Each cc. of the normal acid solution used represents .056 gm. of pure potassa. To find percentage, multiply the factor (.056) by the num- N ber of cc. of V, S. used, and then multiply the prod- uct by 100. Potassium hydroxide having great affinity for carbonic-acid gas, which it absorbs out of the air, generally contains small quantities of carbonate. There- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 44 fore in titrating as above described it should be boiled once or twice toward the end of the reaction in order to drive off any C02 which may be present. This gas, which has an acid reaction with phenolphtalein, would otherwise cause an incorrect estimation. This precau- tion should be taken with the other alkaline hydroxides. The U. S. P. requirement is that 0.56 gm. of potassa be neutralized by not less than 9 cc. of the normal acid solution, each cc. corresponding to 10 per cent of pure potassium hydroxide. The equation is 2KOH + H2S04 = K2S04 4--HaO. 2)_112 2)98 N 56 gms. = 49 gras, in 1000 cc. of —V. S. This shows that 56 gms, of KOH are neutralized by f N 1000 cc. of V. S. 1 Each cc. of this solution will therefore neutralize 0.056 gm. of KOH. Liquor Potassa, U. S. P.—This is an aqueous solu- tion of potassium hydroxide (KOH) containing about 5 per cent of the hydroxide. It is estimated volumetrically in the same manner as potassa, 10 gms. of the solution of potassa being taken, N each cc. of the V. S. representing 0.056 gm. of KOH. By multiplying the factor by the number of cc. of N V. S. used, the quantity of absolute KOH in the 10 gms. of liquor taken is obtained. The percentage is then found by multiplying the quantity so obtained by 100 and dividing by the num- ber of grammes of the liquor taken. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 45 N Thus if 9 cc. of the ~ V. S. were used, the 10 gms. fcaken contained 9 X 0.056 = 0.504 gm. Then io gms. : 0.504 :: 100 : x 5.045. 28 gms. of the U. S. P. liquor potassa should require N about 25 cc. of the acid V. S., each cc. representing ®.2*fc of KOH. Soda, (NaOH|„39 96 a S. P.). I gm. of soda is carefully weighed, dissolved in a small quantity of water, a few drops of phenolphthalein added, and then titrated with normal sulphuric acid V, S. until the red color of the indicator is just discharged. This equa- tion shows the reaction : 2NaOH + H,SO4 = Na2S04 + HgO. 2)30 2)98 N 40 gms. = 49 gms. or 1000 cc. of —V. S. Thus each cc. represents 0.040 gm. of NaOH. 1 gm. N should require 22.5 cc. of acid V. S., which indi- cates go%. .040 X 22.5 = -9°° .QOO x 100 = 9° t Liquor Soda, U. S. P.—This is an aqueous solution, containing about s M Factor.* *1 u cc co c» 6 -t- 04- ( 2 CO * This is the coefficient by which the number of cc. of normal solu tion used is to be multiplied in order to obtain the quantity of pure substance present in the material examined. ACIDIMETRY.—ESTIMATION OF ACIDS BY NEUTRALI- ZATION. In the previous experiments it has been shown how alkalies are estimated by the use of acid solutions of known neutralizing power. In the estimation of acids, which will now be described, the order is reversed, al- kaline solutions of known power being used in deter- mining the strength of acids. Either an alkaline carbonate or an alkaline hydrox- ide may be used in the form of standard solution for this purpose. The hydroxide, however, is to be preferred, for the carbonate when used for titrating an acid gives off car- bonic-acid gas (COa), which interferes to a great extent with the indicators. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 69 In the U. S. P., 1890, volumetric solutions of both potassium and sodium hydroxides are official. The former, however, is preferable, because it attacks glass more slowly and less energetically, and also foams much less than does the sodium hydroxide. The neutralizing power of each is, however, the same. The caustic alkalies and their solutions are very prone to absorb carbon dioxide from the atmosphere. Therefore the solutions often contain some carbonates, the presence of which will occasion errors when used with most indicators, especially litmus and phenolph- thalein. Hence when these indicators or others which are affected by carbon dioxide are used gentle heat should be employed toward the close of each titration to drive off the liberated gas. The standard solutions of alkaline hydroxides should always be preserved in small vials provided with well- fitting cork or rubber stoppers. In order to keep solutions of this kind special ves- sels have been devised (see Fig. 22). The bottle is provided with a well-fitting rubber stopper through which a tube passes, which is filled with a mixture of soda and lime, which absorbs C02 and prevents its ac- cess to the solution. An improvement upon this is shown in Fig. 23, since it allows of the burette being filled without removing the stopper, and consequently without any access of C02 whatever. Preparation of Normal Potassium Hydroxide Vol- umetric Solution, KOH = -j #55*99 contains #55-99 | gms. in 1 litre.—Potassium hydroxide is so prone to ab- sorb carbon dioxide that the pure substance is not 70 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. readily obtained in commerce. If pure potassa were easily obtained it would only be necessary to dissolve 56 gms. in sufficient water to make a litre. But since it always contains some C02 and HaO, it is necessary Fig. 22. Fig. 23. to take a slight excess and dilute the solution to the proper volume after having determined its strength. The U. S. P. process is as follows: Dissolve 75 gms. of potassa in sufficient water to make about 1050 cc. at Js° C. (590 F.), and fill a burette with a portion of this solution. Dissolve 0.63 gm. of pure oxalic acid in about 10 cc. of water in a beaker or flask, add a few drops of phe- nolphthalein T. S., and then carefully add from the A TEXT-BOOK OB VOLUMETRIC ANALYSIS. burette the potassium-hydroxide solution, agitating frequently and regulating the flow to drops towards the end of the operation until a permanent pale-pink color is obtained. Note the number of cc. of the po- tassa solution consumed, and then dilute the remainder so that exactly 10 cc. of the diluted liquid will be re- quired to neutralize 0.63 gm. of oxalic acid. Instead of weighing off 0.63 gm. of the acid, 10 cc. of its nor- mal solution may be used. Example.—Assuming that 8 cc. of the stronger po- tassa solution had been consumed in the trial, then each 8 cc. must be diluted to 10 cc., or the whole of the remaining solution in the same proportion. Thus if 8 cc. must be diluted to 10 cc., 1000 cc. must be di- luted to 1250 cc. 8 : io :: 1000 \ x x = 1250 cc. It is always advisable to make another trial after diluting. 10 cc. should then neutralize 0,63 gm. of pure oxalic acid. Centinormal Potassium Hydroxide V. S., KOH = | contains | fc>m‘ in I litre.—This is ( *56 (0.56 gm. made by diluting 10 cc. of the normal solution with enough distilled water to make 1000 cc. Normal Sodium Hydroxide V. S., NaOH = j 39-96 contains gms. | jn z jjtre>—Dissolve 54 ( *4O 40 gms. ) gms. of sodium hydroxide in enough water to make about 1050 cc. at 150 C. (59° F.), and fill a burette with a portion of this solution. Dissolve 0.63 gm. of pure oxalic acid in about 10 cc. of water in a flask or beaker, add a few drops of phe- nolphthalein T. S., and then carefully add from a burette 72 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. the soda solution, agitating the flask or beaker fre- N quently, as directed under KOH V. S., until a per- manent pale-pink color is produced. Note the number of cc. of soda solution consumed, and then dilute the remainder of the solution so that exactly io cc. will be required to neutralize 0.63 gm. of pure oxalic acid. Example. —lf 8 cc. of the stronger soda solution had been consumed in the trial, then each 8 cc. must be diluted to 10 cc., or the whole of the remaining so- lution in the same proportion. Thus if 980 cc. should be still remaining, this must be diluted with water to make cc. Now make a new trial with the diluted solution to see whether 10 cc. will be required to neutralize 0.63 N gm. of oxalic acid (or 10 cc. of oxalic acid V. S.). N the same as that of potassium hydroxide V. S., and may be employed in place of the latter, volume for volume. The neutralizing power of this solution is exactly The following acids may be tested with either ot these alkaline solutions : Acidum aceticum “ “ dilutum “ “ glaciale “ citricum. “ hydrobromicum dilutum, “ hydrochloricum. “ “ dilutum. “ hypophosphorosum dilutum. u lacticum. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 73 Acidum nitricum. “ “ dilutum. “ phosphoricum. “ “ dilutum, “ sulphuricum. “ “ aromaticum. “ “ dilutum. “ tartaricum. Acidum Aceticum, HC2H302 = | The U. S. P. acetic acid contains 36f0, by weight, of absolute HC2H302 and 64$ of water. Mix 3 gms. of the acid with a small quantity of water, add a few drops of phenolphthalein T. S., and titrate with normal potassium hydroxide V. S. until a permanent pale-pink color is obtained, and apply the following equation ; HC.H.O, + KOH = KQH3O3 + H,O. 60 56 „ N Thus 56 gms. or 1000 cc. of KOH V. S. will neutral- ize 60 gms. of acetic acid ; therefore each cc. of N • KOH V. S. represents .060 gm. of acetic acid. If 18 cc. are required to neutralize 3 gms. of the acid, it contains 18 X -060 = 1.08 gms. of absolute acetic acid. I.oB X ioo —3— = 36*. According to the U. S. P,, 6 gms. of the acid should re- N quire 36 cc. of KOH V. S. for complete neutraliza- tion. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Acidum Aceticum Dilutum.—A solution contain- ing 6s, by weight, of absolute acetic acid. The estimation is conducted exactly as the above. The diluted acetic acid U. S. P. should contain 6$ of absolute acid. 24 gms. should require 24 cc. of - KOH V. S. 1.44Q X 100 _ 24 24 X .060 = 1.440 Vinegar.—Vinegar is impure diluted acetic acid. Its strength may be estimated in the same manner as acetic acid. Phenolphthalein must be used as an indi- cator. Litmus will give only approximate results, be- cause potassium and sodium acetate both have a slightly alkaline reaction with litmus, but show no reaction with phenolphthalein,* The absence of mineral acids must be assured before the volumetric test is applied. The strength of vinegar may also be estimated by distilling no cc. until 100 cc. come over. The 100 cc. will contain 80$ of the whole acetic acid present in the no cc., and may be titrated ; or the specific gravity of the distillate may be taken, and, by consulting the table below, the per cent strength of the distillate found. By adding 20$ to this the strength of the original vinegar is obtained. Vinegar usually contains from 3$ to 6$ of acetic acid. * Even dark-colored vinegar may be titrated in this way when diluted. If the color, however, is too dark, litmus-paper or phenol- phthalein paper may be used by bringing a drop of the liquid in con- tact with the paper from time to time during the titration. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Acetic Acid Table. Per cent of Absolute Acetic Acid. Specific Gravity at-! I5° C- at1 59° F. Per cent of Absolute Acetic Acid. Specific Gravity at ] is: £■ 1 59 F. Per cent of Absolute Acetic Acid. Specific Gravity I 1.0007 26 I.0363 51 x.0623 2 1.0022 27 1.0375 52 1.0631 3 I.OO37 28 1.0388 53 1.0638 4 I.OO52 29 I.0400 54 1.0646 5 I.OO67 30 1.0412 55 x.0653 6 I.OO83 31 I.0424 56 1.0660 7 I.OO98 32 1.0436 57 1.0666 8 1.0113 33 I.0447 58 1.0673 9 I.0127 34 I.0459 59 1.0679 IO I.OI42 35 I.0470 60 1.0685 n I.0157 36 I.0481 61 1.0691 12 1.0171 37 1.0492 62 1.0697 13 1.0185 38 I.0502 63 1.0702 14 1.0200 39 I.05I3 64 1.0707 15 1.0214 40 I.0523 65 1.0712 16 1.0228 4i 1-0533 66 1.0717 17 1.0242 42 1-0543 67 1.0721 18 I.O256 43 1.0552 68 1.0725 19 I.O27O 44 1.0562 69 1,0729 20 I.O284 45 1.0571 70 1-0733 21 I.O298 46 1.0580 71 1-0737 22 1.03II 47 1.0589 72 1.0740 23 I.O324 48 1.0598 73 1.0742 24 1.0337 49 1.0607 74 1.0744 25 1.0350 50 1.0615 75 1.0746 ESTIMATION OF FREE MINERAL ACIDS IN VINEGAR. Mr. Hehner has devised the method given below, which has the merit of being speedy, scientific, and accurate. The method is based upon the fact that acetates of the alkalies are always present in commercial vinegar, and when vinegar is evaporated to dryness, and the ash ignited, the acetates of the alkalies are thus converted into carbonates. If the ash has an alkaline reaction no free mineral acid is present. If, however, the ash is A TEXT-BOOK OF VOLUMETRIC ANALYSIS. neutral or acid some free mineral acid must be present. The quantitative process in detail is as follows : 50 cc. N of vinegar are mixed with 25 cc. of soda or potash V. S. The liquid is evaporated to dryness on a water- bath, and the residue carefully incinerated at the low- est possible temperature, to convert the acetates into N carbonates. When cooled, 2$ cc. of sulphuric acid 10 r V. S. are added, the mixture heated to expel C02 and filtered. The filter is washed with hot water, phenol- phthalein T. S. added, and the filtrate and washings N . N carefully titrated with alkali. Each cc. of alkali 10 10 used represents 0.0049 gm- H2S04 or 0.003637 gm. HCI. Acidum Aceticum Glaciale.—Three grns. of glacial acetic acid are mixed with a small quantity of water, a few drops of phenolphthalein T. S. added, and the solu- N tion titrated with potassium hydroxide V. S. until a very pale pink color appears. Each cc. represents .06 gm. of absolute acetic acid. 49.5 cc. are required by 3 gms. of the U. S. P. acid. 49-5 X .o6 = 2.970 gms. 2.970 X 100 = 99% 3 Acidum Citricum, H3C6H,0,.H20 = | 3.5 gms. of citric acid are dissolved in a sufficient quantity of wrater, a few drops of phenolphthalein added, N and the solution titrated with potassium hydroxide A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 77 V. S. until a very pale pink color appears. Each cc. of N potassium hydroxide consumed before neutralization is effected represents .070 gm. of the pure acid, and 50 cc. should be required. The reaction is expressed by the following equation: + 3KOH = K3C6H5Ot + 4HaO. 3)210 3)168 70 56 Thus 56 gms. of KOH or 1000 cc. of its normal solu- tion represent 70 gms. of pure crystallized acid, and each cc. represents .070 gm. Therefore 50 X .070 = 3.5 gms. 3.5 X 100 = 100$ 3-5 Lime-juice or Lemon-juice, the chief constituent of which is citric acid, may be estimated by titrating N with potassium hydroxide V. S. in the same manner as other acid solutions. Lime-juice contains on an average 7.845, rarely as much as 10#, and very seldom as little as 7$ of citric acid. Commercial lime-juice frequently contains sulphuric, hydrochloric, or tartaric acid. Therefore before apply- ing this test the absence of notable quantities of these acids must be insured by qualitative tests. Acidum Hydrobromicum Dilutum (Diluted Hydro- bromic Acid), HBr = | —A liquid containing 10 78 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. per cent, of pure hydrobromic acid (HBr) and 90 per cent, of water. 8.1 gms. of the acid are diluted with a small quan- tity of water, a few drops of phenolphthalein T. S. N added, and then ~ potassium hydroxide V. S. added from a burette, until a very faint pink color is pro- N duced. Note the quantity of alkali used, and mul- tiply this by the factor .081 gm. to obtain the weight of HBr in the diluted acid taken. The reaction is expressed by the following equation : HBr + KOH = KBr + HaO. N 81 gms. 56 gms. = 1000 cc. of —V. S. Each cc. therefore represents .081 gm., or 1 per cent, of HBr. If this acid is made with tartaric acid and potassium bromide, a white, crystalline precipitate will be pro- N duced upon the addition of the y alkali, some of which will be neutralized by the dissolved potassium bitartrate and the excess of tartaric acid, and an incor- rect indication will be given. ( 36.37 1*364 ' ICIUI'6 containing 31.9 per cent., by weight, of absolute HCI and 68.1 per cent, of water. Acidum Hydrochloricum (Muriatic Acid), HCI = 3 gms. of hydrochloric acid are diluted with a little water, a few drops of phenolphthalein added, and then N - potassium hydroxide V. S.-from a burette, until a A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 79 N faint pink color is produced. Note the quantity of alkali used, and apply the following equation: HCI + KOH = KCI + H2O. N 36.4 gms. 56 gms. = 1000 cc. —V. S N Each cc. of y alkali required before the acid is neu- tralized represents .0364 gm. of pure HCI. 3.64 gms. of the U.S.P. acid should require for com- N plete neutralization 31.9 cc. of - KOH V. S. Diluted hydrochloric acid, U. S. P., contains 10 per cent, of absolute HCI. 3.64 gms. of the diluted acid N should require for neutralization 10 cc. of KOH V. S. Let us assume that the 3 gms. of hydrochloric acid N required 20 cc. of -- KOH V. S. Then 20 X .0364 = .7280 gm. of pure HCI in 3 gms. of the acid. .7280 X 100 ~ = 24.26^ Acidum Hypophosphorosum Dilutum (Diluted Hypophosphorous Acid).—The U. S. P. acid contains 10 per cent, of absolute HPH202 = | A TEXT-BOOK OF VOLUMETRIC ANALYSIS. This acid is estimated in exactly the same way as the acids previously noticed : HPHa02 + KOH = KPH202 + H2O. N 66 gms. = 56 gms. = iooo cc. alkali. N Thus each cc. of y alkali represents .066 gm. of PIPHA- Take 5 gms. of the acid, dilute it with a small quan- tity of water, add a few drops of phenolphthalein T. S., N and titrate with KOH V. S. until a very faint pink N color appears. If 8 cc. of the ~ alkali are used, the 5 gms. contain 8 X .066 = .528 gm. 5 : .528 :: ioo : # = 10.56$ 6.6 gms. of the U. S. P. acid should require for neu N tralization 10 cc. of KOH V. S. 1 Acidum Lacticum, H03H5O3 = | —An or- ganic acid containing 75 per cent., by weight, of abso- lute lactic acid and 25 per cent, of water. 5 gms. of lactic acid are slightly diluted with water, a few drops of phenolphthalein T. S. added, and then the N y KOH V. S. from a burette, until a pale-pink color is produced. Note the quantity of normal alkali used, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. and multiply that number by .090 gm. to get the quan- tity of absolute acid in the 5 gms. taken. HC.HA+ KOH = KC.H.O.+ HtO, N go gms. = 56 gms. = icoo cc. KOH V. S. N and 1 cc. of KOH = .090 gm. of HC3Hs03- N If 40 cc. of y KOH are required for neutralization of the 5 gms. of the lactic acid, then X 4° -°9 3-6o gms. 5 : 3.6 :: ioo :x. x = 72$ Acidum Nitricum (Nitric Acid), HN03= | —The U. S. P. acid contains 68 per cent., by weight, of absolute nitric acid and 32 per cent, of water. Take 3 gms. of nitric acid, dilute with a little water, add a few drops of phenolphthalein T. S., and then N pass into the mixture from a burette potassium hydroxide V. S. until neutralization is effected, and the liquid acquires a faint pink color. Apply the following equation ; HN03 + KOH = KNOa + H„0. N 63 gms. 56 gms. 1000 cc. KOH V. S. N Thus each cc. of KOH V. S. required before neu- tralization is effected represents 0.063 gm. of absolute nitric acid. 82 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N If 30 cc. of the alkali are required, then the 3 gms. contain .063 X 30 = 1.890 gms. 3 : 1.89 : : 100 :x. x = 63$ 3.145 gms. of the U. S. P. acid require 34 cc. of N Y KOH V. S., which corresponds to 68$ of absolute acid. Acidum Nitricum Dilutum, U. S. P., contains 10$ of absolute nitric acid, and is estimated in the same way as the nitric acid. Acidum Phosphoricum (Phosphoric Acid), H3P04 | —The U, S. P. acid contains 85$ of absolute orthophosphoric acid and 15$ of water. Take 1 gm. of phosphoric acid, dilute it with water, add a few drops of phenolphthalein T. S., and titrate N with y potassium hydroxide V. S. until neutralization is complete and the liquid has acquired a faint pink color. H3P04 + 2KOH = K2HP04 + 2H20. 2)98 2)112 N 49 gms. 56 gms, = 1000 cc. -j- KOH V. S. N Thus each cc. of y KOH required represents .049 gm. of absolute orthophosphoric acid. If 1 gm, of the acid requires for neutralization 18 cc. of KOH V. S., it contains I .049 X 18 = .922 gm. or 92.2^ A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 83 0.98 gm. of the U. S. P. acid should require 17 cc. N of KOH V. S., which means 85$ of absolute phos- phoric acid. In the estimation of phosphoric acid litmus cannot be used as an indicator, for the disodic or dipotassic hydric phosphate (Na2HPO4 or K2HP04) which is formed when the standard alkaline solution is added to free tribasic phosphoric acid is slightly alkaline to lit- mus, but not to phenolphthalein. It is recommended, therefore, in order to estimate phosphoric acid alkalimetrically, to prevent the forma- tion of soluble phosphate of the alkali, and to bring the acid into a definite compound with an alkaline earth as follows : The free acid in a diluted state is placed in a flask and a known volume of normal alkali in excess added in order to convert the whole of the acid into a basic salt. A few drops of rosolic acid are now added, and sufficient neutral BaCl2 solution poured in to combine with the phosphoric acid. The mixture is heated to boiling, and while hot the excess of alkali is titrated with acid. 1 The suspended basic phosphate, together with the liquid, possesses a rose-red color until the last drop or two of acid, after continuous heating and agitation, gives a permanent white or slightly yellowish milky appearance, when the process is ended. The volume of normal alkali, less the volume of nor- mal acid, represents the amount of alkali required to convert the phosphoric acid into a normal trisodic or tripotassic phosphate. 84 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. H3P04 + 3KOH = K3P04 + 3H20. 3)98 3)i68 n 32.66 gms. 56 gms. = 1000 cc. of KOH V. S. N Thus 1 cc. of y alkali = .03266 gm. of H3P04 Diluted phosphoric acid is estimated in the same manner. Phosphoric Acid may also be estimated by Stolba’s method, as Ammonia-magnesian Phosphate. 0.2 gm. of phosphoric acid is supersaturated with ammonia water, so as to convert all of the acid into ammonium phosphate and leave an excess of the alkali. H3P04 + 2NH4OH = (NH4)2 hpo4 + 2H20 98 132 An excess of magnesia mixture* is now added in order to precipitate all of the phosphoric acid in the form of ammonia-magnesian phosphate. (NH4)2HPO4 + MgS04 = Mg(NH4)P04 + NH4HS04 132 137 The precipitate is washed, first with ammonia water, and then the ammonia is entirely removed by washing with alcohol of 50$ or 60/0 strength. N cess of hydrochloric acid V. S., a few drops of methyl-orange T. S. added, and the excess of acid The precipitate is now dissolved in a measured ex- * Magnesia Mixture.—Dissolve 10 gms. of magnesium sulphate and 20 gms. of ammonium chloride in 80 cc. of water, add 42 cc. of ammonia water, set aside for a few days in a well-stoppered bottle, and filter. It should never be used freshly made. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 85 N found by titrating back with potassium hydrate. N The difference between the number of cc. of HCI N added and the quantity of KOH used gives the quan- tity of HCI which went into combination with the am- monia-magnesian phosphate. Mg(NH4)P04 + 2HCI = NH4H2P04 + MgCl2. 137 72.8 By consulting the equations given, it will be seen that 72.8 gms, of HCI are equivalent to 137 gms. of Mg(NH4)P04, or 132 gms. of (NH4)2HPO4, or 98 gms. of H3P04. / N\ This means that 1000 cc. of a decinormal (—j solu- tion of HCI, containing 3.64 gms. of the acid, repre- sents of each of these quantities ; and one cc. of N HCI thus represents 0.0049 gm- °f phosphoric acid. In this estimation care must be taken that all free ammonia is removed from the precipitate, and that the whole of the ammonia-magnesian phosphate is decom- N posed by the acid before titration with the alkali. This may be insured by using a rather large excess of the acid and warming. Example.—To the precipitate of ammonia-magne- sian phosphate obtained from 0.2 gm. of phosphoric N acid, 50 cc. of HCI are added. In titrating back 15.3 86 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N cc. of KOH are required. Hence 34.7 cc. of the acid went into combination with the double salt. , .17003 X 100 _ , , , . . . and ——— = 85.01$ of absolute phosphoric acid. This method is said to give good results. Then 34.7 X .0049 = 0.17003 gm., Acidum Sulphuricum, H2S04 = | 97^>2.—U. S. P. sulphuric acid contains 92.5 per cent., by weight, of ab- soluted sulphuric acid and 7.5 per cent, of water. Aromatic Sulphuric Acid U. S. P. contains 18.5$ of absolute sulphuric acid, by weight. Diluted Sulphuric Acid U. S. P. contains 10$ by weight of absolute sulphuric acid. Operate upon 1 gm. of the strong add or upon 5 gms. of either dilute or aromatic sulphuric acid. One gm. of sulphuric acid is diluted with about 10 cc. of water. Add a few drops of phenolphthalein T, S. N and titrate with potassa V. S. until the acid is neu- tralized and the solution has acquired a faint pink N color. Each cc. of alkali solution represents 0.049 gm. of absolute sulphuric acid. The reaction is shown by the following equation H2S04 + 2KOH = k2so4 + 2H20. 2)98 2)112 N 49 gms. 56 gms. = 1000 cc. of KOH V. S. N If 18 cc. of KOH V. S. are required for the com- plete neutralization of the sulphuric acid, then it con- tains 18 X .049 gm. = 0.882 gm. 1 ; 0.882 :: 100 : x x = 88.2$ absolute sulphuric acid. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Diluted Sulphuric Acid is estimated in the same way. Operate upon 5 gms. instead of upon 1 gm. Aromatic Sulphuric Acid contains ethyl sulphuric acid. Therefore in estimating the sulphuric acid in this preparation it must be boiled with water for a few minutes so as to decompose the ethyl sulphuric acid. The mixture is then allowed to cool, and titrated in N the usual manner with KOH V. S., using phenol- phchalein as indicator. The U. S. P. requires that 4.89 gms. when mixed with 15 cc. of water and boiled for several minutes should, after cooling, be neutralized by not less than 18.5 cc. of N - KOH. 1 Acidum Tartaricum (Tartaric Acid), HSC,H4Oa = j 149.64^—j3isso]ve 3.75 gms. of tartaric acid in suffi- ( *l5O J J & dent water to make a solution, add a few drops of phenolphthalein T. S., and then pass into the solution N from a burette y potassium hydroxide V. S. until a faint pink tint is acquired by the solution, and apply the equation H2C4H406 + 2KOH = K2C4H406 + 2H 200 2)150 2)1x2 N 75 gms. 56 gms. = 1000 cc. KOH V. S. Thus each cc. required for the neutralization of the acid represents 0.075 gm. If 50 cc. are required, then 50 X .075 = 375 gms» or Ioo^ 88 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Table Showing the Approximate Normal Factors, etc., for the Acids. Acid. Formula. Molecular Weight. Normal Factors.* Acetic hc2h3o2 60 .060 Citric h3c6h6o,.h2o 210 .070 Hydrobromic HBr 81 .081 Hydrochloric HC1 36-4 .0364 Hypophosphorous hph2o2 66 .066 Lactic hc3h5o3 90 .090 Nitric HN03 63 .063 Phosphoric h3po4 98 .049 Sulphuric h2so4 98 .049 Tartaric. h2c4h4o6 150 •075 Phosphoric, after conversion into a neutral phosphate and N retitrating with acid = 03266 1 Phosphoric acid, as ammonia-magnesian phosphate with decinormal acid = 0049 * This is the coefficient by which the number of cc. of normal solu- tion used is to be multiplied in order to obtain the quantity of pure acid in the sample analyzed. ESTIMATION OF THE SALTS OF THE ALKALINE EARTHS. Standard solution of hydrochloric or of nitric acid is preferred by many operators for the titration of caustic or carbonated alkaline earths. These acids have the advantage over most other acids in forming soluble salts. The hydroxides may be estimated by any of the indicators, but as they readily absorb C02 out of the air, they are generally contaminated with more or less carbonate, and the residual method should be used, i.e., a known excess of standard acid should be added, the mixture boiled to expel any trace of C02, and reti- trated with standard alkali. The carbonates are of course estimated in the same way. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 89 If methyl-orange is used, heat need not be employed, unless it is impossible to dissolve the substance in the cold. A good excess of acid is, however, generally sufficient. Soluble salts of calcium, barium, and strontium, such as chlorides, nitrates, etc., may be readily estimated as follows ; A weighed quantity of the salt is dissolved in water, cautiously neutralized if it is acid or alkaline, phenol- phthalein is added, the mixture heated to boiling, and standard solution of sodium carbonate delivered in from time to time, with boiling until the red color is permanent. This process depends upon the fact that sodium carbonate forms with soluble salts of these bases in- soluble and neutral carbonates. CaCl2 + Na3CG3 = CaC03 + 2NaCL 8a(N03)2 + Na3C03 = BaC03 + 2NaN03. Magnesium salts cannot be estimated in this way, as magnesium carbonate affects the indicator. The alkaline earth salts may also be estimated by dissolving them in water, precipitating the base as car- bonate, with an excess of ammonium carbonate and some free ammonia. The mixture is heated for a few minutes, and the carbonate separated by filtration, thoroughly washed with hot water till all soluble matters are removed, and then titrated with normal acid V. S. as carbonate. Normal Sodium Carbonate V. S.—Na2C03 = I ios-85 contains 5-9-5 ( gins, in 1 litre.—This solu- ( *lO6 -53. tion is made by dissolving 53 gms. of pure sodium car- 90 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. bonate (anhydrous) previously ignited and cooled, in distilled water, and diluting to I litre at 150 C. (590 F.). If pure salt is not at hand the solution may be made as follows: About 85 gms. of pure sodium bicarbonate, free from thiosulphate, chloride, etc., are heated to dull redness (not to fusion) for about fifteen minutes to expel one half of the C02; it is then cooled under a desiccator. When cool, weigh off 53 gms. and dissolve it in distilled water to 1 litre at 150 C. (590 F.). This solution should N neutralize acid V. S. volume for volume. 1 Liquor Calcis (Lime-water), Ca(OH)2 | The U. S. P. directs lime-water to be estimated with decinormal oxalic acid V. S., using phenolphthalein as indicator. Take 50 cc. of lime-water, add a few drops of phenol- N phthalein, and then carefully from a burette oxalic acid V. S. until the red color is just discharged. 20 cc. N of the acid V. S. should be required for the neutra- -10 lization. This corresponds to 0.14 (0.148) per cent, of calcium hydroxide. Ca(OH)2 + H2C204.2H20 = CaC204 + 4H20. 20)74 20)126 3.7 gms. 6.3 gms. or 1000 cc, V, S. N Each cc. of oxalic acid V. S. represents .0037 gm. of Ca(OH)a. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 91 Then .0037 X 20 = 0.0/4 gm. .074 X ioo = 0.148$ 50 Syrupus Calcis, U. S. P. (Liquor Calcis Saccharatus, Br, P.).—This is estimated in exactly the same way as the lime-water, except that the solution is weighed for analysis, not measured, as its specific gravity is much higher than that of water. Calcium Carbonate, CaC03 = ] „ 99-7^—Nometh- ( *lOO od is given for the estimation of calcium carbonate in the Pharmacopoeia, but the following process may be used: Operate upon about 25 grammes. One gm. of calcium carbonate is mixed with 5 cc. of water. A measured excess of normal sulphuric acid V. S. is now added, and the solution boiled to drive off the CO,. Then add a few drops of phenolphthalein N T. S., and titrate with alkali V. S. until a faint pink color is obtained. N Note the quantity of y alkali used, and deduct this N from the quantity of acid first added, and the amount of acid which combined with the calcium is obtained. N Each cc. of acid V. S. represents .05 gm. of CaC03. CaCOg + H3S04 = CaS04 + H2O + COa. 2)100 2)98 50 gms‘ 49 gms. or 1000 cc. acid V. S. 92 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N Assuming that 30 cc, of H2S04 V. S. were added to N the 1 gm. of CaCOa, and that 11 cc. of KOH V. S. were required to bring the mixture back to neutrality, N then 19 cc. of H2S04 were actually required to saturate the CaC03. Therefore .05 X 19 = -95 gm., or 95^. Calcium Bromide, Caßr2 = \ 199-43w—This salt ’ 2 ( *2OO when dissolved in water may be estimated directly with normal solution of sodium carbonate. One gm. of the salt is dissolved in a small quantity of water. The solution is neutralized, if it is acid or alkaline, heated to boiling, a few drops of phenol- N phthalein T. S. added, and the solution titrated with y sodium carbonate V, S. delivered cautiously, with boil- ing, until the red color is permanent. Caßr2 + Na2C03 = CaC03 -f 2Naßr. 2)200 2)106 100 gms. 53 gms. or 1000 cc. Na2COa V. S. 1 N Each cc. of y Na2CO;) V. S. represents o.i gm. of cal- cium bromide. If 9 cc, are used, the salt contains 0.1 X9= .9 gm., or of pure Caßr2. Another way is to add an excess of ammonium-car- bonate solution with some free ammonia to the solu- tion of calcium bromide, in order to precipitate all the base in the form of carbonate. The carbonate is then A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 93 separated by filtration, thoroughly washed with hot water to remove all soluble matters, and then titrated as directed for carbonate. Caßr2 = CaCOs = H2S04. 2)200 2)100 2)98 100 gms. 50 gms. 49 gms. or 1000 cc. V. S. 1 N Each cc. of - acid thus represents o. 1 gm. of Caßr2. See U. S. P. method, page 103. Calcium Chloride, CaC)2 = \ J 10— This salt 2 ( *llO.B may be estimated in exactly the same way as described for the bromide. CaCl2 + Na2C03 = CaC03 + 2NaCI. 2)110.8 2)106 ■ N Tr _ 55.4 gms. 53 gms. or 1000 cc. V. S. 1 N 1 cc. Na2C03 = .0554 gm. of CaCl2. CaCl, = CaCOs = H2S04. 2)110.8 2)100 2)98 55.4 50 49 gms. or 1000 cc. V. S. 1 N 1 cc. H2S04 .0554 gm. of CaCl2. Barium Chloride, BaCl2, and Barium Nitrate, 8a(N03)2.—These two salts are estimated in the same way as the soluble salts of calcium noted in the previous chapter. The factor for BaCl2 is 0.10385 gm., the factor for 8a(N03)2 is 0.13045 gm., using normal volumetric solutions. 94 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Strontium Lactate, Sr(C3H6O3)2-(--3H20 = | 3^' —1.33 gms. of the salt, rendered anhydrous before being weighed, by careful drying at iio° C. (230° F.), is ignited, until most of the carbon has disappeared, and then mixed with 10 cc. of water. A few drops of methyl-orange T. S. are now added, and the mixture N titrated with H„SO, V. S. until a faint red color is 1 produced. N 9.9 cc. of the J acid should be required, correspond- ing to 98.6$ of the pure salt. The first step in this process is to drive off the water of crystallization. (Sr(C.H A). + 3H.0) + heat = Sr(C.H A). + 3H,0; 318.78 264.88 then Sr(CSH6O3)2 + 602 = SrC03 + 5C02 + SHaO. 264.88 147.15 Thus Sr(CsH6o3)a = SrC03= H2SG4. 2)147.15 2)98 132.44 73-57 49 gms. or 1000 cc. y acid V. S. N Thus each cc. of y H2S04 represents 0.13244 gm. of pure anhydrous strontium lactate. If 9.9 cc. are required, then 0.13244 x 9-9 = 1-311156 gms. 1.311156x100 = 98.6$ i-33 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 95 In this process, if the ignition is carried too far, the strontium carbonate is decomposed into strontium oxide. Magnesium salts may be estimated by precipitating as ammonia-magnesian phosphate, and titrating this precipitate as directed for phosphoric acid. 96 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER X. ANALYSIS BY PRECIPITATION. The general principle of this method is that the determination of the quantity of a given substance is effected by the formation of a precipitate, upon the addition of the standard solution to the substance under examination. The end of the reaction is determined in three ways : 1. By adding the standard solution until no further precipitate occurs, as in the estimation of chlorides, etc., by silver nitrate. 2. By the use of an indicator. This may either be contained in the liquid under analysis ; or used exter- nally, by frequently bringing a portion of it in contact with a drop of the liquid during the titration. The titration is continued until the slightest excess of the standard solution is shown by the production of a characteristic reaction with the indicator. 3. By adding the standard solution until a precipi- tate is produced, as in the estimation of cyanogen by standard silver solution. The first of these endings can only be applied with accuracy to silver and chlorine estimations, as the silver chloride which is formed is almost perfectly insoluble and has a tendency to curdle closely by shaking, so as to leave a clear supernatant liquid, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 97 Most of the other precipitates, such as barium sul- phate, calcium oxalate, etc., although heavy and insol- uble, do not readily and perfectly subside, because of their finely divided or powdery nature. They must therefore be excluded from this class. In these cases, therefore, it is necessary to find an indicator which brings them into class 2. The third class comprises only two processes, viz., the determination of cyanogen by silver, and that of chlorine by mercuric nitrate. ESTIMATION OF HALOID SALTS. The estimation of these salts is based upon the powerful affinity existing between the halogens and silver, and the ready precipitation of the resulting chloride, bromide, or iodide. Standard solution of silver nitrate is used for this purpose, and for the sake of exactness and conven- ience is made of decinormal strength, and in many cases it is advisable to use centinormal solutions. The Decinormal ] Silver Nitrate V. S. is offi- Vio / cial. AgN03 = I *6-955 | gms. are contained in i litre.—Dissolve 16.97 gms. of pure silver nitrate in sufficient water to make, at or near 150 C. (590 F.), exactly 1000 cc, 1 litre of this solution thus contains of the molecular weight in grammes of silver nitrate. It is therefore a decinormal solution. If pure crystals of silver nitrate are not readily ob- tainable, and pure sodium chloride is at hand, a solu- tion of the silver nitrate may be made of approximate 98 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. strength, a little stronger than necessary, and then standardized by means of the sodium chloride, as fol- lows :o. 117 gm. of sodium chloride is dissolved in water, and a burette is filled with the solution of silver nitrate to be standardized. The silver solution is now slowly added from the burette to the sodium-chloride solution contained in a beaker until no more precipi- tate of silver chloride is produced. If neutral potassium chromate is used as an indi- cator, the end of the reaction is shown by the appear- ance of yellowish-red silver chromate. This indication is extremely delicate. The silver nitrate does not act upon the chromate until all of the chloride is converted into silver chloride. In the above reaction 20 cc. of silver nitrate should be required. But since the silver-nitrate solution is too strong, less of it will complete the reaction, and the solution must be diluted so that exactly 20 cc. will be required to precipitate the chlorine in o. 117 gm. of NaCl. Thus if 17 cc, are used, each 17 cc. must be diluted to 20 cc., or each 170 cc. to 200 cc., or the entire re- maining solution in the same proportion. After dilution a fresh trial should always be made. Nitrate of silver solution should be kept in dark amber-colored, glass-stoppered bottles, carefully pro- tected from dust. Titration by decinormal silver nitrate V. S. may be managed in various ways, adapted to the special prep- aration to be tested. 1. In most cases it is directed by the U. S. P. to be used in the presence of a small quantity of potassium chromate T. S. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 99 2. In some cases it is added until the first appear- ance of a permanent precipitate, as in potassium cya- nide and hydrocyanic acid. 3. It may be used in all cases without an indicator by observing the exact point when no further precipi- tate occurs. But since this consumes too much time in waiting for the precipitate to subside, so as to render the supernatant liquid sufficiently clear to recognize whether a further precipitate is produced by the addi- tion of the silver solution, it is impracticable. It may, however, be practised in the case of ferrous iodide, where the addition of potassium chromate T. S. would be improper, since it reacts with the iron. 4. It may be added in definite amount, known to be in excess of the quantity required, and the excess measured back by titration with decinormal potassium sulphocyanate V. S., or even with decinormal sodium chloride V. S. (residual titration). N In case an excess of the silver nitrate V. S. is 10 added accidentally, it is only necessary to add a defi- N nite volume of a solution of the salt under exami- -10 N nation, and finish the titration with silver nitrate, 10 deducting, of course, the same number of cc. of silver solution as has been added of the salt solution. Ammonium Bromide, NH4Br = | £^7,—3 givs. of the salt are dried at ioo° C. (212° F.) and dissolved in water to the measure of 100 cc. 10 cc. of this solu- tion are placed in a beaker, a few drops of potassium chromate T. S. added, and then the decinormal silver A TEXT-BOOK OF VOLUMETRIC ANALYSIS. nitrate V. S. carefully added from a burette, until a permanent red coloration is produced. The red col- oration is due to the formation of red chromate of silver, which takes place after all of the bromine has combined with the silver. Apply the equation; NH4Br + AgNOs = Agßr + NH4NQ3. i0)97-77 io)i69-7 N 9.777 gms. 16.97 gms, or 1000 cc. AgN03 V. S. N Thus each cc. of the V. S. represents .009777 gm. of NH4Br. N The U. S. P. salt should require 30.9 cc. of AgNOg V. S. But as a rule this salt contains an impurity (am- monium chloride) which will be precipitated by the silver nitrate as well as the bromide. The presence of this impurity must therefore be taken into account in calculating the percentage of bromide. NH4CI + AgNQ3 = AgCl, + NH4N03. 10)53-38 10)169-7 N 5.338 16.97 gms. = 1000 cc. of V. S. The amount of the salt examined equivalent to N 1000 cc. of silver solution is first calculated by 10 J simple proportion : 30.9 cc. : .3 gm. :: 1000 cc. :x. x = 9.708. Then 9-777 9-7°8 =y■ y = 069. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N .069 = the excess of AgN03 V. S. used up by the ammonium chloride, reckoned in terms of bromide (NH4Br); and since 5.338 gms. of NH4CI = 9 777 gms. of NH4Br, the excess which NH4CI can consume is represented by 9.777 5-338 = 4439. Therefore, as 4-439 : 5-338 :; .069 :z. £=0.08297. 0.08297 = the amount of ammonium chloride present in x grammes of the sample taken. Lastly, calculate the percentage by simple propor- tion : 9.708 : .0829 :: 100 :P. P = 0.85$ of NH4CI. Lithium Bromide, Lißr = | —Dissolve 0.3 gm. of dry lithium bromide in 10 cc. of water, add 2 drops of potassium chromate T. S., and then titrate with decinormal silver nitrate V. S. until a permanent red color of silver chromate makes its appearance. N 0.3 gm. of the U.S. P. salt requires 33.5 cc. of V. S. Lißr + AgN03 = Agßr + LiN03. 10)86.77 10)169 7 N 8.677 gms. 16.97 gms. or 1000 cc. AgNOs V. S, N Thus each cc. of AgNOa V. S. = 0.008677 gm. cf pure lithium bromide. Potassium Bromide, KBr = | —Operate upon o. 1 gm. of the salt dissolved in about 10 cc. of 102 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. water. Add a few drops of potassium chromate T. S., N and titrate with AgN03 V. S. until a permanent red color of silver chromate is produced. According to the U. S. P., 0.5 gm. of the well-dried salt should require 42.85 cc. of AgNOs V. S. KBr + AgN03 = Agßr + KN03 10)118.79 10)169.7 N 11.879 gms. 16.97 gms. or 1000 cc. AgN03 V, S. Thus each cc. represents .011879 gm. of KBr. Po- tassium chloride is a common impurity; to calculate it-, proceed as for NH4CI, 74.4 of KCI being equal to 118.79 KBr. Sodium Bromide, Naßr = | This salt is tested in exactly the same manner as the potassium bromide. A convenient quantity to operate upon is 0.1 gm. The U. S. P. directs that 0.3 gm. of the well-dried salt be dissolved in 10 cc. of water, two drops of potas- sium chromate T. S. added, and the mixture titrated with decinormal silver nitrate V. S. until a permanent red color of silver chromate appears. Note the number of cc. required to produce this effect, and multiply this number by the factor 0.010276 gm. This will give the quantity of Naßr present in the sample taken. According to the U. S. P., not more than 29.8 cc. of the standard silver solution, corresponding to at least 97.29$ of the pure salt, should be required. The chloride which is present as an impurity may A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 103 be calculated in the same manner as ammonium chlo- ride, 5.837 gms. of the chloride being equal to 10.276 gms. of sodium bromide. Calcium Bromide, Caßr21 *200^3.—-This salt may be tested as described on page 92. The U. S. P. method is as follows: 0.25 gm. of the well-dried salt is dissolved in 10 cc. of water; 2 drops of potassium chromate T. S. are then added, and the solution titrated with decinormal silver nitrate V. S. until a permanent red color is produced. 25 cc. of the standard silver-nitrate solution should be required to produce this result, corresponding to 99.7$ of the pure salt, a greater amount of the standard solution indicat- ing the presence of calcium chloride, a smaller amount indicating other impurities. Caßr2 2AgN03 = 2Agßr -f- Ca(NO3)3. 2)199-43 2)339.4 10)99-715 10)169.7 9.9715 gms. 16.97 gms. or 1000 cc. AgNQ3 V. S. 10 N Ihus each cc. of AgN03 V. S. represents .0099715 gm. of Caßr2. Therefore 25 cc. represent .0099715 X 25 = 0.2492875 gm. ■2492875 X 100 = 0.25 ' Strontium Bromide, Srßra -j- 6H20 = | This salt is tested volumetrically, according to the U. S. P., in the following manner: 0.3 gm. of strontium bromide, rendered anhydrous by 104 A TEXT-BOOK OF VOLUMETRIC ANALYSIS, thorough drying before being weighed, is dissolved in io cc. of water, 3 drops of potassium T. S. are added, and then the decinormal silver nitrate V, S. is poured in from a burette until all of the bromide has combined with the silver nitrate and a permanent red coloration is produced. Not more than 24.6 cc. of decinormal silver nitrate V. S. should be required, corresponding to at least 98$ of the pure salt. Srßr2 -f- 2AgN03 = 2Agßr -{- Sr(NO3)2. 2)246.82 2)339'4 10)123.41 10)169.7 N 12.341 gms. 16.97 gms. or 1000 cc. ~ AgNOa V. S. N Thus each cc. of AgN03 V. S. represents 0.012341 gm. of strontium bromide. Zinc Bromide, Znßr2 = | .—This salt is es- timated as follows; 0.3 gm. of the dry salt is dissolved in 10 cc. of water, 2 drops of potassium chromate T. S. are added, and then decinormal silver nitrate V. S. is poured in from a burette until all of the bromide has combined with silver nitrate, and a permanent red color is produced. Note the number of cc. of the standard silver solution used, and multiply this num- ber by the factor shown by the following equation, to obtain the amount of pure zinc bromide in the quan- tity taken: Znßr2 -f- 2AgN03 = 2Agßr -f- Zn(NO3)2. 20)224.62 20)339.4 N 11.231 gms. 16.97 gms. or 1000 cc. AgN03 V. S. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Thus each cc. represents .011231 gm. of pure Znßra. The U. S. P. salt should require 26.7 cc. of decinormal silver nitrate V. S. to produce the desired reaction, cor- responding to not less than 99.95$ of the pure salt. Thus 0.011231 X 26.7 0.2998677 gm. 0.2998677 x 'QQ o*3 Potassium lodide, KI = | —This is esti- mated, according to the U. S. P., in a manner similar to the haloid salts just considered. 0.5 gm. of the well-dried salt is dissolved in 10 cc. of water, 2 drops of neutral potassium chromate T. S. N are added, and then the AgN03 V. S. slowly added from a burette until a permanent red color of silver chromate is produced. Not more than 30.25 cc. nor less than 30 cc. of decinormal silver nitrate V. S. should be required. This quantity corresponds to 99 5$ of the pure salt. KI + AgN03 = Agl -J- KN03. 10)165.56 10)169.7 N 16.556 gms. 16.97 gms. or 1000 cc. AgNOs V. S. N Each cc. of AgN03 V. S. thus corresponds to 0.016556 gm. of potassium iodide, Thus 0.016556 x 30 = 0.49668 gm. 0.49668 X 100 , Q 5 = 99-3$ A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Potassium iodide may also be estimated volumet- N rically by mercuric chloride V. S., the termination 20 of the operation being indicated by the formation of a red precipitate. 4-KI + HgCl2 = 2KCI + HgI2.2K1 (soluble). (1) HgIa.2KI + HgCla = 2KCI + 2HgI2. . (2) This process originated with M. Personne, and is founded on the fact that if a solution of mercuric chlo- ride be added to one of potassium iodide, in the pro- portion of one equivalent of mercuric chloride to four of potassium iodide, red mercuric iodide is formed, which dissolves at once to a colorless solution. The slightest excess of mercuric chloride will cause a bril- liant red precipitate to make its appearance, Hgl2. 4-KI + HgCl, = 2KCI + Hg1,.2K1 (soluble). 20)662.24 20)270.54 33.X12 gms. 13.527 gms. or 1000 cc. of standard solution. Thus each cc. of standard solution of the above strength represents 0.033112 gm. of potassium iodide, which means that 1 cc. is the largest quantity of this standard solution which can be added to 0.033112 gm. of potassium iodide without producing a permanent precipitate. The above solution of mercuric chloride is not N . strictly a— V. S. Potassium iodide is a univalent salt; J 20 and since four molecules of it are precipitated by one molecule of mercuric chloride, the latter is chemically equivalent to four atoms of hydrogen ; and \ of its A TEXT-BOOK OF VOLUMETRIC ANALYSIS. molecular weight in grammes, dissolved in water to N one litre, is a normal solution, and At of this is a •i 0 20 V. S. The author of this process states that neither chlo- rides, bromides, nor carbonates interfere with the re- action. Sodium lodide, Nal = | —Dissolve 0.5 gm. of the well-dried salt in 10 cc. of water, add 2 drops of potassium chromate T. S., and then pass N into the solution from a burette AgN03V. S. until a permanent red coloration is produced. Note the number of cc. used, and multiply this by the factor. Nal 4- AgN03 = Agl + NaN03. 10) 149-53 N 14.953 Sms- 16.97 gms. or 1000 cc. AgN03 V, S. N Each cc. of AgN03 V. S. represents 0.014953 gm of Nal. N Assuming that 33 4 cc. of AgN03 V. S. were re quired, each representing 0014953 gm. of Nal, then the quantity tested contained 334 X 0.014953 gm. or 0.4994302 gm. 04994302 X 100 = 99.8$ 0.5 The U. S. P. requirement is that the salt contain 98$, at least, of pure Na. 108 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Strontium lodide, Srl2 -f- 6H20 = | •—°-3 gm. of strontium iodide, rendered anhydrous before being weighed, is dissolved in 10 cc. of water, 3 drops of potassium dichromate T. S. are then added, and the N AgN03 V. S. run in from a burette until a perma- nent red coloration is produced. Apply the following equation : Srl2 + 6H20 + 2AgN03 = 2AgI +Sr (N03)2 + 6H20. 2)448.12 2)339-4 10)22406 10)169.7 22.406 gms. 16.97 gms. or 1000 cc. AgN03 V. S. N This equation shows that each cc. of the AgNOa V. S. represents 0.022406 gm. of Srl2, C o j j Zinc lodide, Znl2 = | *^lg’ .—Dissolve 0.5 gm. of dry zinc iodide in 10 cc. of water, add 2 drops of po- tassium chromate T. S., and then run into the mixture N from a burette AgN03V. S. until a permanent red color is produced, indicating that all of the iodide has been precipitated in the form of silver iodide. Each cc. N of the silver solution used represents 0.015908 gm. of zinc iodide. Znl2 + 2AgN03 = 2AgI + Zn(No3)a 2)318.16 2)339-4 10)159.08 10)169.7 N 15.90S gms. 16.97 gms. or iooocc. AgN03 V. S, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The U. S. P. directs that not less than 31 cc. nor N more than 31.4 cc. of AgN03 V. S. be required to produce the desired result, 31 cc. corresponding to 98.62$ and 31,4 cc. to 99.9$ of pure zinc iodide. 0.015908 x 3r-4 = 0,4995112 gm. of Znl2. Then 0.4995112 X ioo - Q>s = 99-9$ Ammonium Chloride, NH4CI | *^3-38_.—It is estimated in the same manner as the other soluble haloid salts. A weighed quantity of the salt is dissolved in a small quantity of water and the solution titrated with N silver-nitrate solution until no more precipitation takes place, or, if potassium chromate T, S. has been added as indicator, until a red color makes its appear- ance. NH4CI + AgN03 = AgCl -f NH4NOs. 10)53-38 10)169.7 N 5.338 gms. 16.97 gms. or 1000 cc. - V. S N Thus each cc. of V. S. used represents 0.005338 gm. of NH4CI. Potassium Chloride, KCI | —Thisisesti- ( 74-4° mated in the same manner as the above, applying the following equation : KCI + AgNOs = AgCl + KN03. r0)74-4 10)169.7 N 7.44 gms. 16.97 gms. or 1000 cc. AgNOs V. S. 110 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N Thus each cc. of V. S. represents 0.00744 gm. of KCI. Sodium Chloride, NaCl = | —A weighed quantity of the well-dried salt, say 0.2 gm., is dissolved in about 10 cc. of water and the solution mixed with N a few drops of potassium chromate T. S. Then AgN03 V. S. is run in from a burette until all the chloride is precipitated and a permanent red color of silver chromate is produced. The U. S. P. directs that 0.195 gm. of the salt should N require not less than 33.4 cc. of AgN03 V. S. to pro- duce this reaction. The following equation shows the reaction which takes place between the sodium chloride and the silver nitrate: NaCl + AgN03 = AgCl + NaN03. io)fB-37 5.537 gms. 16.97 gms. or 1000 cc. ~ AgN03 V. S. Each cc. of the standard solution thus represents 0.005837 gm. of NaCl. .005837 X 33-4 = 0.194958 gm. of NaCl. o.iq4QsB X ioo = 99.9$ 0.195 Zinc Chloride, ZnCl, = | *^s-84—This sa]t is tested in exactly the same way as the other haloid salts. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Dissolve 0.3 gm. of the dry salt in about 10 cc. of water, add a few drops (2 drops) of potassium chromate N T. S., and then run into the mixture from a burette, 10 AgN03 V. S. until a permanent red color is produced. It should require 44.1 cc. of the standard silver solu- tion to produce this result. The reaction is shown by the following equation ZnCl2 + 2AgN03 = 2AgI + Zn(No3)a. 2)135-84 2)339.4 10) 67.92 10)169.7 N 6.792 gms. 16.97 gms. or 1000 cc. V. S. N Thus it is seen that each cc. of the AgNO, V. S. 10 & 3 represents 0.006792 gm. of ZnCl2. 0.006792 X 44-1 = 0.2995272 Sm* 0.2995272 X 100 0 . O:3 = 99-84^ Syrupus Acidi Hydriodici, a syrupy liquid contain- The U. S. P. requires 99.84^. ing about lie of HI U. S. P. HI = | Oper- ate upon 15 grammes. The reaction which occurs is as follows : HI + AgN03 = Agl -f- HNOa. io)i27-5 io)i69-7 N 12.75 gtns. 16.97 gms. or 1000 cc. AgNOs V. S. The end of the reaction is shown by the cessation of the formation of a precipitate. 112 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Since nitric acid is liberated, potassium chromate is not admissible as indicator. The U. S. P. directs that the syrup be neutralized by ammonia water before titration. This prevents the formation of nitric acid, and admits of the use of potassium chromate as indicator. (31.875) *32 gms. of the syrup, neutralized, and mixed with 2 drops of the indicator, should require 25 cc. of decinormal silver-nitrate solution to produce a permanent red tint. Each cc. represents 0.01275 gm. of HI. 0.01275 X 25 = 0.31875 gm. 0.31875 X 100 , 31-875 Syrupus Ferri lodidi, a syrup containing about 10io by weight of ferrous iodide (Fela) U. S. P.FFesls = I *309 2 Sms- syruP> m'x with a N small quantity of water, and run in the silver solu- tion. The close of the reaction is shown by the cessa- tion of the formation of a precipitate. Potassium chromate is not admissible as an indicator in this case. Fel2 + 2AgNOs = 2AgI + Fe(NO,)s. 2)308.94 2)339.4 10)154-47 10)169.7 N 15.447 gms. 16.97 gms. or 1000 cc. V. S Thus each cc. represents 0.015447 gm. of ferrous iodide. The U. S. P. method originated with Volhard. It has the advantage over the direct method for haloids A TEXT-BOOK OF VOLUMETRIC ANALYSIS. with chromate indicator, in that it may be used in the presence of nitric acid. It thus enables the haloids to be estimated in the presence of a phosphate or other salt which precipitates silver in a neutral, but not in an acid solution. It depends upon entirely precipitating the chloride, in the presence of nitric acid, by a known excess of standard solution of silver nitrate, and then estimating the excess of silver left uncombined, by the aid of a standard solution of potassium sulphocyanate, using ferric alum as an indicator. The sulphocyanate has a greater affinity for silver than it has for iron, and therefore so long as any silver is in solution, the sulphocyanate will combine with it and form a precipitate of silver sulphocyanate. As soon as the silver is all taken up, the sulphocya- nate will combine with the ferric alum and strike a brownish-red color. The sulphocyanate solution is to be made of such strength that it corresponds with the silver solution, volume for volume. The difference between the volume of silver solu- tion originally added, and the volume of sulphocyanate solution used, will give the volume of silver solution equivalent to the haloid salt present. Decinormal Potassium Sulphocyanate V. S. (Vol- hard’s Solution), KSCN = | *96-99 9&99 | gms. in i litre,—Dissolve 10 gms. of pure crystallized potas- sium sulphocyanate (thiocyanate) in 1000 cc. of water. This solution, which is too concentrated, must be adjusted so as to correspond in strength exactly with decinormal silver nitrate V. S. For this purpose in- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N troduce into a flask 10 cc. of AgNO, V. S., 0.5 cc. 10 of ammonio-ferric sulphate T. S., and 5 cc. of diluted nitric acid. Run into this mixture from a burette the sulphocya- nate solution. At first a white precipitate of silver sulphocyanate is produced, giving the fluid a milky appearance, and then, as each drop of sulphocyanate falls in, it is sur- rounded by a deep brownish-red cloud of ferric sulpho- cyanate, which quickly disappears on shaking, as long as any of the silver nitrate remains unchanged. When the point of saturation is reached and the silver has all been precipitated, a single drop of the sulphocyanate solution produces a faint brownish-red color, which does not disappear on shaking. Note the number of cc. of the sulphocyanate solu- tion used, and dilute the whole of the remaining solution so that equal volumes of this and of the decinormal silver nitrate V. S. will be required to pro- duce the permanent brownish-red tint. (The same tint of brown or red to which the volumetric solution is adjusted must be attained when the solution is used in volumetric testing.) Assuming that 9.5 cc. of the sulphocyanate solution were required to produce the reaction, then each 9.5 cc. must be diluted to make 10 cc., or the whole of the remaining solution in the same proportion. Always make a new trial after the dilution to see if the solutions correspond. The U. S. P. method for estimating syrup of ferrous iodide is as follows: 1-5447 gms. (*1.55 gms.) of the syrup and 10 cc. of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. water are introduced into a flask, 11 cc. of decinormal silver nitrate V. S. are added, then 5 cc. of diluted nitric acid, and 5 cc. of ferric ammonium sulphate T. S. The decinormal potassium sulphocyanate V. S. is now run into the mixture from a burette until a reddish- brown tint is produced, which does not disappear upon shaking. Not more than I cc. should be required. This corresponds to 10$ of ferrous iodide. The re- actions which take place are shown by the following equations; Fel, + 2AgNO, = 2AgI + Fe(NO>),; . (i) N 15.447 gms. 16.97 gms. or 1000 cc. —AgNO3 V. S. 10 AgNOa + KSCN = AgSCN + KN03; . (2) N 16.97 gms. 9.699 gms. or 1000 cc. —KSCN V. S 10 Fea(NH4)a(S04)4 + 6KSCN = Fe2(SCN)6 + (NH4)aSO4 + 3K2504. (3) The Fea(SCN)6 gives the brownish-red color to the solution. The object of the nitric acid is to acidulate the solu- tion, facilitate the precipitation of the silver, and to oxidize the ferrous nitrate. In the above case 11 cc. of silver nitrate are originally added. If 1 cc. of potassium sulphocyanate be re- quired, it shows that 1 cc. of the silver-nitrate solution was in excess, and that 10 cc. went into combination with the ferrous iodide. The equation shows us that A TEXT-BOOK OF VOLUMETRIC ANALYSIS. each cc. of silver nitrate V. S. represents 0.015447 gm. of ferrous iodide ; then 10 cc. represent 0.015447 X io = 0.1544; gm., , .15447 X 100 and = 10$ 1-5447 of Fel2 in the U. S. P. syrup. Saccharated Ferrous lodide.—The process for estimating this compound is exactly the same as that for syrup of ferrous iodide. 1.5447 gms, (*1.55 gms.) of the saccharated ferrous iodide are dissolved in about 20 cc. of water in a small flask, and to this solution is added first 22 cc. of N AgNOa V. S., then 5 cc. of diluted nitric acid, and N 5 cc. of ferric ammonium sulphate T. S. The J r 10 KSCN V. S. is then run in, from a burette, until the reddish-brown color of ferric sulphocyanate is produced. N Not more than 2 cc. of the KSCN V. S. should be 10 required. This corresponds to of pure ferrous iodide. N 22 cc. of silver nitrate 10 2 cc. of potassium sulphocyanate f N = 20 cc. of silver nitrate, 10 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. which reacted with the ferrous iodide, then 0.015447 X 20 = 0.30894 gm., 0.30894 X 100 ~ 20% 1-5447 Syrup of Ferrous Bromide, U. S. P. 1880, Feßr2 = I *2l6—This syrup may be tested in the same manner as the syrup of ferrous iodide, either by the direct method, using the cessation of precipitation as the end reaction, or by the residual method with potassium sulpho- cyanate. The factor is 0,01077. Hydrocyanic Acid, HCN = | —Dilute hy- drocyani cacid may be estimated by weighing out about 5 gms., and adding to this sufficient soda or potassa solution to convert the acid into sodium or potassium cyanide (NaCN or KCN), and leave the solution strongly alkaline. To this solution is added the decinormal silver- nitrate solution until a permanent turbidity occurs. This turbidity is due to the precipitation of silver cyanide, and affords a delicate proof of the completion of the reaction. The difficulty experienced in this process is in the conversion of the acid into the cyanide. The sodium cyanide has a strong alkaline reaction, turning litmus blue when only a small proportion of the acid has been neutralized. If the titration is conducted before the acid is com- pletely neutralized, that which is free will not be acted A TEXT-BOOK OF VOLUMETRIC ANALYSIS. upon. Indeed, cyanide of sodium may be estimated in the presence of hydrocyanic acid in this way. According to Senier, the following procedure will answer well: To the dilute hydrocyanic acid add soda solution to a strong alkaline reaction, determined by litmus tinc- N ture. Then titrate with silver nitrate V. S., drop io r by drop, from the burette. If the liquid becomes acid, add a little more soda solution to bring it back to alkalinity, and continue the titration until the turbidity indicates the end of the reaction. The liquid must be kept alkaline throughout the process. It is not well to add too much soda solution at the beginning, as this would use up too much of the silver solution, and make the reading a trifle too high. The following equations, etc., explain the reactions: 2HCN + 2NaOH = 2NaCN + 2HaO ; 10)53.96 10)97.96 5.396 gms. 9.796 gms. 2NaCN + AgN03 = AgCN,NaCN + NaN03. i0)97-6 10)169.7 9.796 gms. 16.97 gms. or 1000 cc. V. S, It is seen that 5.396 gms, of real HCN are equivalent to 9.796 gms. of sodium cyanide, and represent 16.97 N gms. of silver nitrate, or 1000 cc. of the —V. S, That 10 N is, 1000 cc. of the -- AgNOa V. S. may be added to a solution containing 9.796 gms. of sodium cyanide, and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. no precipitate be produced ; but if one or two drops more of the standard solution be added, a precipitate is at once formed. N Each cc. of AgN03 V. S., which fails to produce a precipitate with a solution of sodium cyanide, repre- sents 0.009796 gm. of NaCN, which is equivalent to .005396 gm. of HCN. With 2 molecular weights of sodium or potassium cyanide, one molecule of silver nitrate forms a double salt, having the composition NaCN,AgCN, and which is soluble. When more silver-nitrate solution is added, this solu- ble double salt is decomposed, and a precipitate of silver cyanide occurs, thus: AgCN,NaCN + AgN03 = 2AgCN -f- NaN03. The U. S. P. method is as follows; A weighed quantity of the acid is mixed with suffi- cient of an aqueous suspension of magnesia to make an opaque and decidedly alkaline mixture. To this a few drops of potassium chromate T. S. are N added, and the silver solution delivered from a 10 burette until the red color of silver chromate appears. 1.35 gms- the diluted acid is mixed with enough water and magnesia to make an opaque mixture of about 10 cc. Add to this 2or 3 drops of potassium chromate T. S., and then from a burette deliver the decinormal silver nitrate V. S. until a red tint is pro- duced which does not again disappear by shaking. 120 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Each cc. of the standard silver solution used, repre- sents 0.002698 gm. of absolute HCN, HCN + AgN03 = AgCN + HN03 10)26.98 10)169.7 N 2.698 gms. 16.97 gms. or 1000 cc. silver nitrate V. S. Potassium Cyanide, KCN = —This salt may be estimated in the following manner : 1 gm. of the salt is dissolved in sufficient water, and into the solution, is delivered in drops the standard silver solution until a precipitate appears which is not redissolved on agitation. If 0.65 gm. of KCN are taken, not less than 45 cc. of N AgN03 V, S. should be required. 2KCN + AgN03 = AgCN,KCN -|- KN03. 10)130.02 10)169,7 13.002 gms. 16.97 gms. or 1000 cc. AgN03 V. S. Thus each cc. of the standard silver solution repre- sents 0.013 gm. of KCN. 0.0i3 X 45 = gm. .585 X 100 , = 9°* Cyanides maybe estimated also by iodine, according to Fordos and Gelis. This process depends upon the fact that potassium cyanide decolorizes iodine, potassium iodide and cyanogen iodide being formed. When iodine solution is added to a solution of po- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 121 tassium cyanide, the iodine is decolorized as long as there is any undecomposed cyanide present. The following equation expresses the reaction KCN + I, = KI -f CNI, 2)65.01 2)153.06 10)32.505 10)126.53 N 3.2505 gms. 12.653 gnis. or 1000 cc. iodine V. S. Thus each cc. of the volumetric solution represents 0.00325 gm. of KCN. The end of the reaction is known by the yellow color of the iodine solution becoming permanent. Silver Nitrate, (Argenti Nitras) AgN03= | —Nitrate of silver and other salts of this metal may be volumetrically estimated by standard solution of sodium chloride. The silver salt is dissolved in sufficient water in a beaker, and a decinormal volumetric solution of sodium chloride run in until a precipitate is no longer pro- duced. The estimation may also be performed by retitration as follows : To the silver solution contained in a beaker add a N measured excess of - sodium chloride V. S., and then, 10 after adding a few drops of potassium chromate T. S., N titrate the mixture with silver nitrate V. S. until a 10 permanent red color appears. Deduct the number of cc. of silver nitrate V. S. from the quantity of sodium chloride V. S. and the quantity of the latter is ob- tained which actually combined with the silver solution under examination. 122 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The sulphocyanate method of Volhard may also be employed in the estimation of silver. ~ Sodium Chloride V. S., NaCl = | . | §ms- 1 litre-—Dissolve 5.837 gms. of pure sodium chloride in enough water to make exactly 1000 cc. at the ordinary temperature of the atmos- phere. Check this solution with decinormal silver nitrate V. S. The two solutions should correspond, volume for volume. Pure Sodium Chloride may be prepared by passing into a saturated aqueous solution of the purest com- mercial chloride of sodium a current of dry hydro- chloric-acid gas. The crystalline precipitate is then separated and dried at a temperature sufficiently high to expel all traces of free acid. The U. S. P. method for silver nitrate is as follows ; ’x’°-34 Brn- (0-3391 gm.) of silver nitrate is dissolved in 10 cc. of distilled water, and the solution carefully N titrated with NaCl V. S. until precipitation ceases. 20 cc. of the standard solution should be required. AgN03 + NaCl = AgCl + NaNO,. 10)169.55' 10)58-37 N 16.955 gms. 5.837 gms. or 1000 cc. NaCl V. S. Each cc. of the standard solution represents 0.01695 5 gm. of pure AgN03. 0.016955 x 20 = 0.3391 gm- -0.3391 X 100 , - y = 100$ •339 i A text-book of Volumetric analysis. 123 Argenti Nitras Dilutus (Mitigated Caustic).—This may be estimated in the same manner as the above. The U. S. P. method is as follows : 1 gm. is dissolved in 10 cc. of distilled water, to this N is added 20 cc. of NaCl V. S. and a few drops of N potassium chromate T. S., and the excess of NaCl 10 N V. S. found by titration with AgN03 V. S. until a permanent red color is produced. Not more than 0.5 cc. of the latter should be required. This indicates N that 19.5 cc. of NaCl V. S. were actually required to completely precipitate the silver nitrate tested. Therefore 0.016955 X 20 = .3306225 gm. ■33 + IXIOO =33+ i< Argenti Nitras Fusus (Moulded Silver Nitrate. Lunar Caustic).—This is treated in exactly the same manner as the above. 0.34 gm. of the lunar caustic is dissolved in water, and 20 cc. of standard sodium chloride added ; not more than 1 cc, of this should be in excess, as shown by retitration with silver nitrate V. S., using chromate indicator. This corresponds to about 95$ of pure silver nitrate. Silver Oxide, AgsO = 231.28.—May be converted into nitrate by solution in nitric acid, and then test- ing as above for silver nitrate. There will prob- ably be some free nitric acid present if this is done, 124 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. and therefore the sulphocyanate method is best em- ployed. The Sulphocyanate Method.—A weighed quantity of the silver salt is dissolved in water, some diluted nitric acid and ammonium ferric sulphate solution are N added, and the mixture then titrated with potassium io sulphocyanate V. S. until a permanent reddish-brown color of feric sulphocyanate is produced. The following equation explains the reactions: AgN03 + KSCN = AgSCN + KN03. 10)169.55 10)96.99 16.955 gms. 9.699 gms. or 1000 cc. standard V. S. Thus each cc. of the standard V. S. represents 0.016955 gm. of pure silver nitrate, or 0.010766 gm. of metallic silver. Liquor Plumbi Subacetatis (Goulard’s Extract).— This is an aqueous solution containing about of lead subacetate, the formula of which is approximately Pb20(C2l I 302)2 = 546.48. This is estimated by precipi- tation with sulphuric acid. (13.6622 gms.) *13.67 gms. of the solution are diluted with 50 cc. of water, a few drops of methyl-orange added, and the mixture titrated with normal sulphuric acid until the lead is completely precipitated and the mix- ture has assumed a red color. The red color indicates an acid reaction. The reaction is illustrated by the following equation : Pb10(CsH,o*),+2HaS04=2PbS04 + 2HC2H302 + Hao. 4)546.48 4)196 N 136.62 gms. 49 gms. or 1000 cc. - H2S04 V. S. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 125 N Thus each cc. of H2S04 V. S. represents 0.13662 gm. of the subacetate. If 25 cc. of the standard solution are required, then the solution under analysis contains 0.13662 X 25 = 3.4155 gms. 3.4155 X 100 13.662 The Diluted Solution of Lead Subacetate (Lead Water) may be estimated in the same manner. 126 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Table of Substances Esi imated by Precipitation, giving Formula, Molecular Weight, Standard Solution used, and Factor. Name. Formula. Molec- ular weight. Standard Solu- tion Used. Factor. HBr 80.76 N -AgNOs 10 0.008076 HCN 26.98 N — AgNG3 10 O.OO2698 HI 127-53 . 97-77 53-38 M4-S4 !99.43 no 65 215.40 308.94 O.OI275 Ammonium bromide “ chloride NH4Br NH4Cl nh4i (4 O.OO9777 o. 005338 0.014454 CaBr2 CaClj FeBr2 Fel2 (4 0.0099715 0.005532 44 0.01077 — AgNOj and 10 N — KSCN 10 0.015447 Pb(C2H302)2.3H2 0 378.0 N — h2so4 0.189 Pb20(C2H302)2 546.48 4k 0.13662 N -AgNO, Lithium bromide LiBr 86.77 0.008677 KBr 118.79 3 44 0.011879 0.00744 0.01300 0.016556 0.0096QQ KCl KCN KI KSCN 65.ox 165.56 96.99 (4 “ iodide “ sulphocyanide N — NaCl or 10 N — KSCN Aga 215.32 0.010766 AgN03 AgaO NaBr 169.5S 0 44 0.016955 0.011564 0.010276 44 102.76 N - AgN03 NaCl Nal SrBr2.6H20 SrI2.6H20 ZnBr2 ZnCl2 Znl2 58.37 J49.53 354-58 448.12 224.62 135-84 318.16 IO 44 0.005837 4; Strontium bromide.. .. “ 0.012341 0.022406 44 0.006792 0.015908 “ iodide “ A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 127 CHAPTER IX OXIDIMETRY—ANALYSIS BY OXIDATION. An extensive series of analyses are made by this method, with extremely accurate results—in fact, the results are generally more accurate than any which can be obtained by weighing. The principle involved in this method is extremely simple. Substances which are capable of absorbing oxygen or are susceptible of an equivalent action are subjected to the action of an oxidizing agent of known power, and the quantity of the latter required for complete oxidation ascertained. The substances which are used as oxidizing agents in volumetric analysis are potassium dichromate, po- tassium permanganate, iodine, etc. The reducing agents, or deoxidizers, are sodium, thio- sulphate, oxalic acid, arsenous oxide, stannous chloride, metallic zinc, and magnesium. Thus ferrous oxide (FeO), an oxidizable substance, is ever ready and willing to take up oxygen, while potassium dichromate and permanganate are always ready to give up some of their oxygen. When po- tassium permanganate gives up its oxygen in this way it loses its color, and in volumetric analysis advantage is taken of this fact. When the permanganate, which is added in drops from a burette, is no longer decolor- 128 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. ized, the iron salt is completely oxidized. The reac- tion is as follows: loFeO + 2KMn04 = 5Fe203 -J- 2MIIO -f- K2O. Ferrous oxide. Ferric oxide. The oxidation of ferrous oxide by potassium dichro- mate is shown by the following equation : 6FeO -j- K2Cr20, 3Fe203 -j- Cra03 -f- K2O. An oxidation is always accompanied by a reduction, the oxidizing agent being itself reduced in the opera- tion. As seen in the above equations, the manganic compound is reduced to a manganous compound, and the chromic to a chromous compound. ESTIMATION OF FERROUS SALTS. Ferrous salts are estimated by oxidizing them either with potassium dichromate or potassium perman- ganate. In some respects the dichromate possesses advan- tages over permanganate. 2. Its solution does not deteriorate upon standing as does that of permanganate. 1. It may be obtained in a pure state. 3. It is not decomposed by contact with rubber as the permanganate is, and may therefore be used in Mohr’s burette. Its great disadvantage, however, is that when used in the estimation of ferrous salts the end reaction can only be found by using an external indicator. The indicator which must be used is freshly A TEXT-BOOK OF VOLUMETRIC ANALYSIS. prepared potassium ferricyanide T. S, a drop of which is brought in contact with a drop of the solution being tested, on a white slab, at intervals during the titration, the end of the reaction being the cessation of the production of a blue color, when the two liquids are brought together. Thus the estimation by potas- sium dichromate is cumbersome, and very exact results are not easily obtained. If potassium-permanganate solution is used for the estimation of these salts the end of the reaction is easily found without the use of an indicator. The permanganate is decomposed the instant it is brought in contact with a ferrous salt in an acid solu- tion ; therefore as long as any ferrous salt remains in solution the permanganate is decolorized, and when it ceases to lose its color the reaction is complete. Preparation of Standard Solution Decinormal Potassium Dichromate V. S., KsCraOT = | | £ms* *n 1 tre-— gms. (*4 9gms.) of pure potassium dichromate are dissolved in sufficient water to make, at the ordinary temperature of the atmos- phere, exactly 1000 cc. Pure Potassium Dichromate for use in volumetric analysis should respond to all the tests for purity given in the text of the U. S. P. (under Potassii Dichromate), as wrell as to the following: A solution of o 5 gm. of the salt in 10 cc. of water, rendered acid by 0.5 cc. of nitric acid, should produce no visible change when treated with barium chloride T. S. (absence of sulphate), nor with silver nitrate T. S. (absence of chloride). If a mixture of 10 cc. of an aqueous solution of the 130 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. salt (I—20) with I cc. of ammonia water be treated with ammonium oxalate T. S., no precipitate should be pro- duced (absence of calcium). Standard solution of potassium dichromate is some- times used as a neutralizing solution for estimating alkalies, phenolphthalein being used as indicator. When used for this purpose the decinormal solution contains 14.689 gms. in I litre (one half the molecular weight in grammes). It is then the exact equivalent of any decinormal acid V. S. Decinormal potassium dichromate V. S. may also be used in conjunction with potassium iodide and sul- phuric acid for standardizing sodium thiosulphate V. S. lodine is liberated from potassium iodide in this reac- tion. The reaction is expressed by the equation K2CrA + 6KI + 7H2504 = 4K2504 + Cr2(S04)3 + 7H20 + 3lt. When used as an oxidizing agent to convert ferrous into ferric salts, or to liberate iodine from potassium N iodide, the solution of potassium dichromate must contain 4.689 gms. in 1 litre. If the decinormal solution containing 14.689 gms. in 1 litre is used, it has the effect f 3N , . of a solution. 10 The decinormal solution which is used as an oxidizing agent is chemically equivalent to decinormal potassium permanganate. When used for the purpose of liberating iodine from potassium iodide, it is the equivalent of an equal volume of decinormal sodium thiosulphate. For titrating ferrous salts the decinormal solution of dichromate is used in the following manner: A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Make an aqueous solution of the ferrous salt, intro- duce it into a flask, and acidulate it with sulphuric or hydrochloric acid. Now add gradually from a burette the decinormal potassium dichromate V. S. until a drop taken out upon a white slab no longer shows a blue color with a drop of freshly prepared potassium ferricyanide T. S. Note the number of cc. of the standard solution used, multiply this number by the factor, and thus obtain the quantity of pure salt in the sample taken. Ferrous salts strike a blue color with potassium ferricyanide T. S ; but as the quantity of ferrous salts gradually diminishes during the titration, the blue be- comes somewhat turbid, acquiring first a green, then a gray, and lastly a brown shade. The process is finished when the greenish-blue tint has entirely disappeared. The reaction of potassium dichromate with ferrous salts always takes place in the presence of free sul- phuric or hydrochloric acid at ordinary temperatures. Nitric acid should not be used. If it is desired to estimate ferric salts by this standard solution it is necessary to first reduce them. This may be done by metallic zinc, magnesium, sul- phurous acid, the alkali sulphites, or by stannous chloride. Standard potassium dichromate may be checked in the same way as standard permanganate, with pure metallic iron, as described below. Decinormal Potassium Permanganate V. S., 2KMn04 = | *^5It contains | Sms- *n 1 litre.—This solution may be prepared by dissolving the pure crystals in fresh distilled water. If the salt can be 132 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. obtained perfectly pure and dry, a decinormal solution will be obtained if 3.1534 gms. are dissolved in distilled water, sufficient to make 1000 cc. at the ordinary atmos- pheric temperature ; but nevertheless it is always well to verify it as described below. The solution will retain its strength for several weeks if well kept, but it should always be checked by titration before it is used. The standardization of permanganate solution may be effected as follows : With Metallic Iron—Thin annealed binding-wire, free from rust, is one of the purest forms of iron. 0.1 gm. of such iron is placed in a flask which is provided with a cork through which a piece of glass tubing passes, to the top of which a piece of rubber tubing is at- tached, which has a vertical slit about one inch long in its side, and which is closed at its upper end by a piece of glass rod (see Fig. 24). Diluted sulphuric acid is added and gentle heat ap- plied. The iron dissolves and the steam and liberated hy- drogen escape through the slit under slight pressure. The air is thus prevented from enter- ing and the ferrous solution Fig. 24. protected from oxidation When the iron is completely dissolved a small quan- tity of cold, recently boiled, distilled water should be added, and the titration with potassium permanganate at once begun and continued until a faint permanent A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 133 red color is produced. If the solution is decinormal, exactly 17.85 cc. will be required to produce this result. The iron is converted by the sulphuric acid into ferrous sulphate, Fe2 -j- 2H2S04 = 2FeS04 -f- 2H2. This ferrous sulphate is easily oxidized by the air, and therefore it is directed that access of air should be prevented, and the distilled water, with which the solu- tion is diluted, previously boiled in order to drive off any dissolved free oxygen. ioFeS04 -j- 2KMn04 -f- 8H2S04 100)558.8 100)315.34 5.588 gms. 3-1534 gins. or 1000 cc. V. S. 10 = 5Fe2(504)3 + K2S04 + 2MnS04 + 8H20. N This equation, etc., shows that each cc. of 2KMn04 V. S. represents .005588 gm. of metallic iron. With Oxalic Acid.—0.063 gm. of the pure crystal- lized acid is weighed (or 10 cc. of decinormal oxalic acid V. S. carefully measured) and placed in a flask, with some dilute sulphuric acid and considerable water, the mixture warmed to about 6o° C. (140° F.), and the permanganate added from a burette. The action is in this case less decisive and rapid than in the titration with iron, and more care should be used. The color disappears slowly at first, but afterwards more rapidly. Note the number of cc. of the permanganate solu- tion used, and then dilute the remainder so that equal volumes of decinormal oxalic acid and decinormal permanganate solution will exactly correspond. 134 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Example.—Assuming that 9 cc. of the perman- ganate solution first prepared had been required to produce a permanent pink tint when titrated into 10 N cc. of oxalic-acid solution, then the permanganate must be diluted in the proportion of 9 of permanganate and 1 of distilled water, or 900 and 100. The U. S. P. gives the following method for the preparation of this solution : A stronger and a weaker solution is made and mixed in certain proportions to form a solution of the proper strength. It is said that when thus prepared the solu- tion will keep its titre for months if properly preserved. The Stronger Solution.—3.s gms. of pure crystallized permanganate are dissolved in 1000 cc. of water by the aid of heat, and the solution then set aside in a closed flask for two days, so that any suspended mat- ters may deposit. The Weaker Solution.—Dissolve 6.6 gms, of the salt in 2200 cc. of water in the same manner as above, and set this solution aside for two days. These two solutions are then separately titrated in the following manner; Introduce 10 cc. of decinormal oxalic-acid solution into a flask, add 1 cc. of pure concentrated sulphuric acid, and before the mixture cools add the perman- ganate solution slowly from a burette, shaking the flask after each addition, and towards the end of the operation reducing the flow to drops. When the last drop is no longer decolorized, but imparts a pinkish tint to the liquid, the reaction is completed. Note the number of cc. consumed. Finally, mix the two solu- tions in such proportions that equal volumes of the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 135 N mixture and of oxalic acid V. S. will exactly corre- spond. To obtain the accurate proportions for mixing the two solutions, deduct io from the number of cc. of the weaker solution consumed in the above titration ; with this difference multiply the number of cc. of the stronger solution consumed : the product shows the number of cc. of the stronger solution needed for the mixture. Then deduct the number of cc. of the stronger solu- tion consumed in the titration from io, and with the difference multiply the number of cc. of the weaker solution consumed ; the product shows the number of cc. of the weaker solution needed for the mixture. Or, designating the number of cc. of the stronger so- lution by and the number of cc. of the weaker solu- tion by W, and using the following formula, the proportions in which the solutions must be mixed are obtained: Stronger Solution. Weaker Solution {IV-10 )S + (io-5)fF. Example.—Assuming that 9 cc. of the stronger and 10.5 cc. of weaker had been consumed in decomposing N 10 cc. of oxalic acid V. S. ; then, substituting these values in the above formula, we obtain (io-5 ~ 10)9 + (io ~ 9)io.S, or 4.5 + 10.5, making 15 cc. of final solution. 136 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The bulk of the two solutions is now mixed in the same proportion : 450 cc. of the stronger and 1050 cc. of the weaker, or 900 cc. of the stronger and 2100 cc. of the weaker. After the solutions are thus mixed a new trial should be made, when 10 cc. of the solution should exactly N decompose 10 cc. of oxalic acid V. S. The reaction between potassium permanganate and oxalic acid is illustrated by the following equation: 2KMnO, + 5(HaCa04.2H20) + 3H2504 = K2S04 + 2MnS04 + ioC02 + i 8H20. ESTIMATION OF FERROUS SALTS WITH POTASSIUM BICHROMATE. One molecule of potassium dichromate yields, under favorable circumstances, three atoms of oxygen for oxidizing purposes. This is shown by the following equation ; 6FeO + K2Cr207 = 3Fe2Os + Cr203 + K2O. Here it is seen that the three liberated atoms of oxygen combine at once with the ferrous oxide, con- verting it into ferric oxide ; 6FeO -j- 03 = Fec09 or 3Feso3. When used for oxidizing, the reaction takes place only in the presence of an acid. The dichromate then gives up its oxygen. Four of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 137 its oxygen atoms combine at once with the replaceable hydrogen of the accompanying acid, the other three being liberated. The three oxygen atoms thus set free are available either for direct oxidation or for combination with the hydrogen of more acid. In the latter case a corresponding quantity of acidulous radi- cals is set free. The following equation indicates this reaction : K,Cr.O, + 4H.SO. = K.SO.+ 0.(50.). + 4H.0 + O, In this case four of the liberated atoms of oxygen combine with eight of the atoms of hydrogen of sul- phuric acid and liberate four S04 radicals, which at once combine with the K2 and Cr2 of the dichromate. The other three atoms are set free. If seven sulphuric- acid molecules are used instead of four molecules, the three free atoms of oxygen will liberate 3(S04): K.Cr,O,+7H,SO.=K,SO.+ Cr,(50.).+7H,0 + {SO.).. If this liberation of 3(504) takes place in the pres- ence of a ferrous salt, the 3(504) will combine with six molecules of the ferrous salt, converting it into a ferric salt ; 6FeS04 + 3504 = Fe6(S04)9 = 3Fe2(504),; 6FeS04 + K2Cr20, + ;H2SO4 = K2S04 -f Cr2(S04)3 + ;H2O + (3Fe2(504)3). If in the above case hydrochloric acid is used instead of sulphuric, fourteen molecules of the former must be taken to supply the necessary hydrogen. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The seven liberated atoms of oxygen must have fourteen atoms of hydrogen to combine with. Three of these atoms of oxygen liberate six uni- valent, or three bivalent, acidulous radicals. Therefore, since one molecule of K2Cr20, will give up for oxidizing purposes three atoms of oxygen, which are equivalent chemically to six atoms of hydro- gen, one sixth of the molecular weight in grammes of the dichromate, dissolved in sufficient water to make one litre, constitutes a normal solution, and one tenth of this quantity of K2Cr20, in a litre, a decinormal solution. Thus the estimation of ferrous salts is effected by oxidizing them to ferric with an oxidizing agent of known power, the strength of the ferrous salt being determined by the quantity of the oxidizing agent required to convert it to ferric. Ferri Carbonas Saccharatus (Saccharated Ferrous Carbonate), FeC03 = | 73.—*1.16 (1.1573) gms. of saccharated ferrous carbonate are dissolved in 10 cc. of diluted sulphuric acid and the solution diluted with water to about 100 cc. The decinormal potassium dichromate is carefully added, until a drop of the solu- tion taken out and brought in contact with a drop of freshly prepared solution of potassium ferricyanide ceases to give a blue color. The number of cc. of the dichromate solution is read off and the following equations applied : 6FeC03 + 6H2S04 = 6FeS04 + 6H20 + 6C02; H5-73 iSi-7 6 6 694.38 910.2 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 139 then 6FeC03 or 6FeS04 + K2Cr207 + ;H2SO4 = 6)694.38 6)910.2 6)293.78 10)115.73 10)151-7 10) 48.96 11-573 gms. 15.17 gms. 4.896 gms., or 1000 cc. F K3Cr207 V.S. IO KaS04 + Cr2(S04)3 + ;H2O + 3Fe,(504),. N Thus each cc. of K2Cr207 represents 0.011573 gm. of pure ferrous carbonate or 0.005588 gm. of metallic iron. The U. S. P. saccharated ferrous carbonate requires N about 15 cc. of K2Cr207 V. S. for complete neutral- ization, corresponding to about 15$. .011573 X 15 = 0.173585 gm. 0.173585 X 100 j ryo I-1573 If strong sulphuric acid is added to saccharated fer- rous carbonate it will char the sugar, and a black mass of burnt sugar is obtained. This may be prevented by adding water first and then, slowly, the sulphuric acid. Instead of sulphuric acid, hydrochloric acid may be used. This will not char the sugar ; but the ferrous chloride which is then formed is too readily oxidized by the air. It has also been suggested that as hydrochloric acid so rapidly converts ordinary sugar into invert sugar as to render it easily attacked by the dichromate, it should be cautiously used, if at all. Phosphoric acid 140 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. has none of these disadvantages, and may be employed with good results. In making estimations of ferrous salts with potas- sium dichromate, care should be taken to avoid atmos- pheric oxidation. It is good practice to calculate approximately how much of the standard solution will probably be required to complete the oxidation, and then add almost enough of the standard solution at once, instead of adding it slowly. A white porcelain slab is then got ready, and placed alongside of the flask in which the titration is to be performed. Upon this slab is placed a number of drops of the freshly prepared solution of potassium ferricyanide, and at intervals during the titration a drop is taken from the flask on a glass rod and brought in contact with one of the drops on the slab. The glass rod should always be dipped in clean water after having been brought in contact with a drop of the indicator. When a drop of the solution ceases to give a blue color on contact with the indicator, the reaction is complete. Ferrous Sulphate, FeSQ4 + 7H20 = | 2-— Dissolve about one gramme of crystallized ferrous sul- phate in a little water, add a good excess of sulphuric or hydrochloric acid, titrate with the decinormal potas- sium dichromate V. S. as directed under Ferrous Car- bonate, and apply the following equation ; 6(Fe504.7H20) + K2Cr2Q7 + ;H2SO4 = 10) 278 10) 48.96 27.8 gms. 4.896 gras,, or 1000 cc. K2Cr2O7 V. S. 10 6)1668 6)293.78 3^e2(504)3 -f~ K2S04 -f- Cr3(S04)8 -j- 49H20. A TEXT-BOOK OF VOLUMETRIC ANALYSTS, 141 Thus each cc. of the K2Cr207 V. S. represents 0.0278 gm. of crystallized ferrous sulphate or 0.0152 anhydrous. If I gm. of the salt is taken and dissolved as above, it should require about 37 cc. of the standard solution, equivalent to about 100$. Anhydrous Ferrous Sulphate.— 6FeS04 -f K2Cr207 + 7H2504 = 6)912 6)293.78 10)152 10)48.96 N 15.2 gras. 4.896 gras., or 1000 cc. K2Cr207 V. S. 3Fe2(504)3 -f- K2S04 -f- Cr2(S04)s -)- /H2O. Each cc. of the standard solution represents 0.0152 gm. of real ferrous sulphate or *.0056 gm. of metallic iron. Dried (Exsiccated) Ferrous Sulphate of the U. S. P. has the approximate composition FeS04 -}- 3H20. It is tested in the same manner as the anhydrous ferrous sulphate. Granulated Ferrous Sulphate, FeS04 7H20, is tested in the same manner as crystallized ferrous sul- phate, with which it should correspond in strength. ESTIMATION OF FERROUS SALTS WITH POTASSIUM- PERMANGANATE SOLUTION. The action of potassium permanganate in oxidation is very similar to that of the dichromate. The molecule 2KMn04 has 8 atoms of oxygen, which it gives up in the process of oxidation. These 8 atoms of oxygen unite with the replaceable hydrogen 142 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. of an accompanying acid, liberating an equivalent amount of acidulous radical. Three of these atoms of oxygen liberate sufficient acidulous radical to combine with the potassium and manganese of the permanganate, while the other five atoms are available either for direct oxidation or 2KMn04 + 3H2SO4=K2SO4+2MnSO4+ 3H2O+ 50. For combination with the hydrogen of more acid, more acidulous radical being liberated Jto combine with the salt acted upon, 2KMn04+BH9S04=KaS04+2MnS04+BHiO+5(S04). 5(504) when combined with ioFeS04 forms Fe10 (S04)1B or 5Fe2(504)3, ferric sulphate. It is thus seen that one molecule of potassium per- manganate 2KMn04 has the power of converting 10 molecules of a ferrous salt into the ferric state. The equation in full is ioFeS04 + 2KMn04 + 8H.,504 = K2S04 + 2MnS04 + 8H20 + 5Fe2(504)3. We have seen that 2KMn04 has 5 atoms of oxygen available for oxidizing purposes, and that each of these will combine with 2 atoms of hydrogen. 2KMn04 is consequently chemically equivalent to 10 atoms of re- placeable hydrogen, and a normal solution of this salt when used as an oxidizing agent is one that contains in I litre one tenth of the molecular weight of 2KMnO,, and a decinormal solution one which contains one hundredth of the molecular weight, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 143 When potassium permanganate is brought in contact with a ferrous salt or other oxidizable substance, it is decomposed and decolorized. When titrating with a standard solution of this salt it is decolorized so long as an oxidizable substance is present; as soon, however, as the oxidation is com- pleted the standard solution retains its color. The end of the reaction, therefore, when permanga- nate is used, is the appearance of a permanent faint-red color. This is the principal advantage which permanganate has over dichromate. When titrating with standard permanganate solution a glass stop-cock burette should be used, as the solu- tion is slightly affected by the rubber on Mohr’s bu- rette. Ferrum Reductum is estimated for metallic iron, according to the U. S. P., in the following manner: 0.56 (0.559) gm* °f reduced iron is introduced into a glass-stoppered bottle, 50 cc. of mercuric chloride T. S. are added, and the bottle heated on a water-bath for one hour, agitating frequently, but keeping the bottle well stoppered. 2HgCJ2 + Fe2 = 2FeCl2 + 2Hg. Then allow it to cool, dilute the contents with water to 100 cc., and filter. Take 10 cc. of the filtrate, add to it 10 cc. of diluted sulphuric acid, introduce the mixture into a glass-stoppered bottle (having a capacity of about 100 cc.), and titrate the mixture with decinormal potassium permanganate V. S. until a permanent red color is produced. 144 A text-book of volumetric analysis. Each cc. of the standard solution represents *0.0056 gm. of metallic iron, or 10$. ioFeS04 + 2KMn04 + 8H2S04 = K3S04 + 2MnS04 + 5Fe2(504)3 + 8H20. To confirm the assay, add a few drops of alcohol to decolorize (or decompose) the excess of permanga- nate, then add I gm. of potassium iodide, and digest for half an hour at a temperature of 40° C. (104° F.). Fe2(S04)3 + 2KI = 2FeS04 -f I 2 + K2S04. 2)112 2)254 10) 56 10)127 5.6 12.7 The cooled solution is mixed with a few drops of starch test solution, which gives it a dark-blue color, because of the formation of iodide of starch. Then add carefully, from a burette, decinormal sodium thiosul- phate V, S. until the blue color is discharged. IB+ 2(Na„590,.5Ha0) = 2NaI -f NaaS,Oe+ ioH20. 2)254 2)495.28 10)127 10)247.64 N 12.7 gms. 24 76 gms. or 1000 cc. Na2S203 V. S. Thus each cc. of the standard thiosulphate repre- sents 0.0127 gm. of iodine, or 0.0056 gm. of metallic iron. In both of these estimations the quantity of standard solution used should be the same. The U. S. P. requirement is 8 cc. 0.0056 X 8 = 0.0448 gm. 0.0448 X 100 •—— == 80$ 0.056 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 145 Ferrous Sulphate (Crystallized), FeS04 -f-7H20 = | *^7b'^2'—'*1*39I*39 (1*3871) gms* °f ferrous sulphate are dissolved in about 25 cc. of water, and the solution acidulated with sulphuric acid. Decinormal potassium permanganate V. S. is then delivered in from a burette until a permanent pink color is obtained, indicating the complete oxidation of the ferrous salt. io(FeSO4 + ;H3O) + 2KMn04 + 8H2S04 = 100)2774.2 100)315.34 27.742 gms. 3.1534 gms. or 1000 cc. stand- -10 ard solution. 5Fe2(504)3 + K2S04 + 2MnS04 + 8HaO. Thus each cc. of the standard solution represents 0.027742 gm. of crystallized ferrous sulphat®. Not less than 50 cc. should be used before the po- tassium permanganate ceases to be decolorized. 0.027742 X 5° = 1.387100 gms. 1.387100 X 100 —^—— 100$ 1.3871 Granulated Ferrous Sulphate, FeS04 7H20, is esti- mated in the same way as the foregoing, and should correspond with it in strength. Exsiccated {Dried) Ferrous Sulphate.-—This salt is tested in the same manner as the other two sulphates. It contains a larger percentage of ferrous sulphate than the other two, having less water of crystallization. Its composition is approximately FeS04 -j- 3H20. In estimating ferrous sulphate in this salt the water of crystallization is not taken into account. Then by 146 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. deducting the percentage of ferrous sulphate from 100 the percentage of water of crystallization is obtained. ioFeS04 + 2KMn04 + 8H2S04 100)1520 100)315.34 15.20 gms. 3-1534 gms. or 1000 cc. standard solution. 10 = SFe,(SO(). + K,SO, + 2MnSO. + BH.O. Each cc. of the standard solution represents 0.0152 gm. of anhydrous (real) ferrous sulphate. If one gm. of the dried salt, treated as above -described, requires 48 cc. of permanganate solution, it contains 0.0152 X 48 = 0.7296 gm., or 72.96$ of real ferrous sulphate, and 100.00 72.96 = 27.04$ of water of crystallization. Any salt may be analyzed in this way for water of crystallization. If the salt is pure, the difference be- tween the percentage of real salt and 100 always repre- sents the percentage of water of crystallization. ESTIMATION OF HYPOPHOSPHOROUS ACID, HYPOPHOS- PHITES, AND OTHER OXIDIZABLE SUBSTANCES. Acidum Hypophosphorosum Dilutum.—An aque- ous solution containing about 10 per cent, by weight, of absolute hypophosphorous acid. (H.PO,) HPH.O. = | ,^'88. N This acid may be tested by neutralization with potassium hydrate V. S., as described in Chapter X. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 147 The U. S. P. also directs the estimation by residual titration, given below. 0.5 gm. of diluted hypophosphorous acid is mixed with 7 cc. of sulphuric acid, and 35 cc. of decinormal potassium permanganate V. S., and the mixture boiled for fifteen minutes. The potassium permanganate, in the presence of sulphuric acid, oxidizes the hypophosphorous acid to phosphoric, as the equation shows: SHPHA + 6HsS04 + 2(2KMnO4) 2)329.40 2)630.68 100)164.7 100)315.34 1.647 gms. 3-1534 gms. or 1000 cc. V. S. 10 5H3P04 6H„O -f- 2K2S04 -(- 4MnSO4. Each cc. of the decinormal V. S. represents 0.001647 gm. of absolute hypophosphorous acid. The quantity of permanganate solution directed to be added is slightly in excess. The excess is then ascertained by retitration with decinormal oxalic acid V. S. Each cc. of oxalic acid required corresponds to one cc. of deci- normal permanganate V. S., which has been added in excess of the quantity actually required for the oxida- tion. The excess of permanganate colors the solution red, and the oxalic acid V. S. is then added until the red color just disappears, which indicates that the excess of permanganate is decomposed. 2KMnO, + 5(H,C.0..2H.0) + 3H,SO. = KsSO, + 2MnS04 + iSH.O + ioCO,. If 4.7 cc. of decinormal oxalic acid V. S. are required, it indicates that 35 cc. 4.7 cc. = 30.3 cc. of deci- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. normal permanganate were actually used up in oxidizing the hypophosphorous acid. Therefore 0.001647 gm. X 30.3 = 0.0499 Sm-> 0.0499 X ioo or = 9.98$ of HPH202. In the above process the boiling facilitates the oxida- tion, but if the acid is boiled before it is completely oxidized it will decompose. Hence the necessity for adding an excess of the permanganate and retitrating. Calcium Hypophosphite, Ca(PH2O2)2 = | 67. —O.l gm. of the salt is dissolved in 10 cc. of water, then 10 cc. of sulphuric acid and 50 cc. of decinormal potassium permanganate V. S. are added, and the mix- ture boiled for fifteen minutes. The excess of permanganate is then found by reti- trating with decinormal oxalic-acid solution. The reactions which take place are expressed by the following equations : SCa(PH A), + 5H,504 = jCaSO. + 10HPH A: (i) ioHPH2Oa + I 2H2S04 + 4(2KMnO4) = ioH3P04 + I 2H20 + 4K2504 + BMnS04. (2) These two reactions may be written together thus : SCa(PH A). + 17H.50. + 4(2KMnO.) 4)348.35 4)1261.36 100)212.08 r00) 315-34 [ard V. S. = SCaSO, + 4K2504-f BMnS04+ ioH3P04+12H?0. 2.1208 gms. 3.1534 gms. or 1000 cc. stand- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 149 Thus each cc. of the standard permanganate repre- sents 0.0021208 gm. of pure Ca(PH2O2)2. 50 cc. of decinormal potassium permanganate are about 3 cc. more than is necessary to oxidize 0.1 gm. of pure cal- cium hypophosphite. Therefore not more than 3 cc. of the standard oxalic-acid solution should be required to decolorize the solution to which 50 cc. of perman- ganate has been added. Then 0.0021208 gm. x 47 .09968 gm. 0.9968 X 100 = pure salt. Ferric Hypophosphite, Fe2(PH202)g = | —This salt is estimated in the same manner as the fore- going. o. 1 gm. is dissolved in 10 cc. of water, then 10 cc. of sulphuric acid and 50 cc. of decinormal potassium per- manganate V. S. are added, and the mixture boiled for 15 minutes. The quantity of permanganate solution here added is slightly in excess of the quantity actually required to oxidize the hypophosphite. The excess is deter- mined by retitrating with decinormal oxalic acid V. S., which corresponds volume for volume with the per- manganate. Not more than 3 cc. of the standard oxalic acid so- lution should be required to decolorize the excess of permanganate, which means that 47 c.c. of the per- 150 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. manganate should actually be required to oxidize the o. i gm. of hypophosphite taken. The reaction is illustrated by the following equation : SFe2(PHA)e+SiH,SO4+i2(2KMnO4) 12)2505.20 12)3784.08 100) 208.77 100) 315.34 N vs 2.0877 gm. 3.1534 gms.or iooocc.lo SFea(SO4)3+K2SO4-(-24Mn50.4+30H3P04-[-36H20. N This shows that each cc. of potassium permanga- nate V. S. represents 0.0020877 gm. of ferric hypophos- phite. If 47 cc. are required to oxidize 0.1 gm. of the salt, the latter contains 0.0020877 X 47 = 0.098 i-f- gm., or 98.1 -f- f of pure salt. Potassium Hypophosphite, KPH202 = | 91. —o. 1 gm. of dry potassium hypophosphite is dissolved in about 10 cc. of water, then 7.5 cc. of sulphuric acid and 40 cc. of decinormal potassium permanganate V. S. are added, and the mixture is boiled for 15 minutes. Decinormal oxalic acid is then carefully delivered into the mixture until the red color, due to the excess of permanganate, is discharged. The number of cc. of the standard oxalic acid required for this purpose, sub- tracted from the 40 cc. of permanganate originally added, gives the quantity of permanganate which was actually required for the oxidation of the hypophos- phite. If the salt conforms in purity to the U. S. P. requirement, not more than 2 cc. of the oxalic acid V. S. will be required. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 151 The following equation illustrates the reaction which takes place in this operation : SKPHA + 6H2S04 + 2(2KMnO ) 2)519-55 2)630.68 100)259.77 100)315.34 2-5977 gm. 3.1534 gms. or 1000 cc. permaganate V. S. = SKHJPO4 + 2K2S04 + 4MnSO4 + 6 H2O. Each cc. of decinormal permanganate V. S. required for the oxidation of the hypophosphite, represents 0.0025977 gm. of the pure salt. If 38 cc. are required, then 0.0025977 X3B = .0987126 gm., or 98.7+ 56. Sodium Hypophosphite, NaPH202 4- H2O | *lO6—0,1 SirK *s dissolved 10 cc. of water and mixed with 7.5 cc. sulphuric acid and 40 cc. of decinormal potassium permanganate V. S. The mixture is then boiled for 15 minutes, and titrated with decinormal oxalic-acid solution to determine the excess of permanganate. Not more than 3 cc. of the oxalic acid V. S. should be required to discharge the red color, which means that 0.1 gm. of the salt should require 37 cc. of N permaganate solution for its oxidation. The following equation shows the reaction: S(NaPHtO,.HtO) + 6H2S04 + 2(2KMnO4) = 2)529.2 2)630.68 100)264.6 100)315.34 2.646 gm. 3.1534 gm., n or 1000 cc. V.S. SNaH2PO4 -f 2Na2S04 + 4MnSO4 +ll H,O. 152 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Thus each cc. of the decinormal permanganate repre- sents 0.002646 gm. of NaPH202. Aqua Hydrogenii Dioxidi U. S. P. (Solution of Hydrogen Peroxide).—It is described in the U. S. P. as an aqueous solution of hydrogen dioxide, H202 = Therefore 0.002646 X 37 = 0.097902 gm. or 97.95. 1 2, slightly acid and containing about by 1 34 weight, of pure dioxide, corresponding to 10 volumes of available oxygen. This substance is official for the first time in the U. S. P. 1890, in which methods for its preparation, preservation, and assay are given. Solution of hydro- gen peroxide is an important commercial product, being used in the arts as well as in medicine. It is sold as containing 5, 10, 15, or 20 volumes of oxygen, in solution. This should mean that a given volume of the solution yields from itself 5, 10, 15, or 20 times its own volume of oxygen. Thus, 1 cc. of a 5-volume solution yields 5 cc. of oxygen ; a 10-volume solution is one of which 1 cc. will yield 10 cc. of oxygen ; etc. Many solutions of hydrogen dioxide are sent into the market under false pretences, being labelled as con- taining 10, 15, or 20 volumes of oxygen. It is true a given volume of these solutions will yield the specified volume of oxygen when decom- posed with potassium permanganate, but half of this oxygen comes from the permanganate itself. There- fore the peroxide of hydrogen solution contains only half as much available oxygen as is given off in this decomposition. Freshly bought samples of the five largest manufac- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 153 turers, according to the analyses of Dr. Edward R. Squibb (Ephemeris, vol. iv. No. 2), gave 9.2, 8.7, 8.4, 10.9. 9.7, 8.6, 8.5, 7.3, and 7.4 volumes. All of these were labelled as being of 15 volumes strength. The author has had a similar experience. In its purest and most concentrated form peroxide of hydrogen is a syrupy colorless liquid, having an odor resembling that of chlorine or ozone. One cc. of this concentrated hydrogen peroxide when decomposed at o° C. evolves 330.3 times its own volume of oxygen, at a pressure of 760 mm. at 450 N. latitude. At a temperature of ioo° C. (2120 F.) H2Oa decom- poses rapidly into water and oxygen. This change also takes place at ordinary temperatures, but more slowly. In diluted solutions it is more stable, and may be concentrated by boiling without suffering much de- composition. Dr. Squibb made a series of experiments in order to prove this, as well as the fact that solutions of hydro- gen peroxide when kept in open vessels at the ordi- nary temperature become stronger, instead of weaker as was generally supposed. The water evaporates more rapidly than the peroxide decomposes. Part of the results of these experiments as published in the Ephemeris, vol. IV. No. 2, is as follows: A freshly made solution that yielded 10.3 volumes of available oxygen was taken as the basis of the ex- periment. The evaporation was done on a water-bath, at temperatures varying from 550 to 62° C. (131° to 143.6° F.); one cc. of the concentrated solution being taken out for testing after each evaporation. 200 cc. evaporated in 2 hours to roo cc. tested 20.6 volumes: no apparent loss. 154 a text-book of volumetric analysis. ioo cc. of the 10.3-volume solution were added, and evaporated in 2 hours to 100 cc., tested 29.6 volumes: 1.3 volumes loss. 100 cc. of the 10.3-volume solution were added, and evaporated in 2 hours to 100 cc., tested 36.5 volumes: 4.7 volumes loss. 100 cc. of the 10.3-volume solution were added, and evaporated in 2.5 hours to 23 cc., tested 146.8 volumes. Another series of evaporations were made at higher temperatures, which also showed an increase in strength, but the loss was a little larger. I —The U. S. P. method is as follows: ( 34 10 cc. of the solution are diluted with water to make 100 cc. Transfer 17 cc. of this liquid (containing 1.7 cc. of the solution of H202) to a beaker, add 5 cc. N of diluted sulphuric acid, and then from a burette potassium permanganate V. S. until the liquid just retains a faint-pink tint after being stirred. The Assay of Hydrogen Peroxide, H„0„ The reaction is expressed by the following equation: SH.O. + 2KMnO. + 3H,SO( 100)169.6 100)315.34 N 1.696 gms, 3-1534 gms. or 1000 cc. permanganate V. S. *100)170. 10 1.70 = K2S04 + 2MnS04 + 8H20 + sO2. N Thus each cc. of the potassium permanganate represents .001696 (*.0017) gm. of absolute hydrogen dioxide. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 155 The U. S. P. requires that 1.7 gms. of the solution of N peroxide should decolorize 30 cc. of permanganate solution. 1 This corresponds to 3 per cent, by weight, of H202. .0017 X 3° = -OSI gm* .051 X 100 = 3^ 1.7 07 the above equation in a different light. Estimation of Volume Strength.—Let us look at We there see that when potassium permanganate and hydrogen peroxide react, 10 atoms of oxygen are liberated. The permanganate itself when decomposed liberates five atoms of oxygen. Therefore of the above ten atoms only five come from the peroxide of hydrogen. 5H202 5H20 -f- 5O ; 2KMn04+3H2S04 = K2S04+2MnS04+ 3H20 + 50. In order to find the factor for volume of available oxygen, see the following equation, etc.; 5H202+ 2KMn04 -(- 3H2504 100)315.34 N 3*ls34gms- or 1000 cc. of IQ V. S. = K2S04 + 2MnS04 + 8H20 +SO + 50. 100)79.8 .798 gm. 100) 80 *.BO gm. 156 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. . N Thus it is seen that each cc. of potassium per- manganate represents .000798 (*.0008) gm. of oxygen. But we wish to find the volume of oxygen, not the weight represented by 1 cc. of the permanganate. 1000 cc. of oxygen at o° C. and 760 mm. pressure weigh 1.424488 grammes, *(1.43 gms.), Therefore, if 1.43 gms. measure 1000 cc., .0008 gm. will measure x. X 0-5594 cc. iooo X .0008 = 0.5594 cc. 1.43 The factor, then, for volume of oxygen, liberated N when peroxide of hydrogen is titrated with potas- sium permanganate is 0.5594, and the number of cc. N of the potassium permanganate consumed in the titration gives the volume of oxygen liberated by the quantity of hydrogen peroxide taken. N Thus if 30 cc. of the V. S. were required, 0.5594 X 30 = 16.782 cc. of oxygen, 1.7)16.782 9.87 volume strength or the number of cc. of oxygen liberated by 1 cc. of the peroxide solution tested. It is convenient to operate upon 1 cc. hydrogen- peroxide solution. Then each cc. of potassium per- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 157 manganate V. S. used will represent 0.5594 cc. of avail- able oxygen, or 0.0008 gm. of oxygen, and it is only necessary to multiply the cc. by these numbers to obtain the volume or weight of available oxygen. Hydrogen-peroxide solution may also be volumetri- cally assayed by Kingzett’s method, which is described in the chapter on lodimetry. The gasometric estimation is also described further Barium Dioxide (Barium Peroxide), Ba02 = | ’^2>—This substance is assayed by treating it with an acid, and then estimating the liberated hydro- gen dioxide, as follows : Weigh off 2.11 gms. of the coarse powder, put it in a porcelain capsule, add about 10 cc. of ice-cold water, then 7.5 cc. of phosphoric acid, U. S. P., and sufficient ice-cold water to make 25 cc. Stir and break up the particles with the end of the stirrer until a clear or nearly clear solution is obtained, and all that is soluble is dissolved. 5 cc. of this solution (which corresponds to 0.422 gm. of barium dioxide) is measured off for assay. Drop into this from a burette, with constant stirring, decinormal potassium permanganate V. S. until a final drop gives the solution a permanent pink tint. Not less than 40 cc. of the decinormal permanganate V. S. should be required to produce this result. In this process, the first step is the formation of hy- drogen peroxide by treating the barium peroxide with phosphoric acid, as illustrated by the following equa- tion : Ba02-f H3P04 = BaHPO, + HaO,. 158 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The hydrogen peroxide is then estimated with deci- normal permanganate V. S. SHA + 2KMn04+3H,S04 100)169.6 100)315.34 N 1.696 gms. 3.1534 gms. or 1000 cc. permanganate V. S. 100)1.70 10 *1.70 = K2S04 + 2MnS04 +BH2O + sO2. N Thus each cc. of potassium permanganate V. S. represents 0.001696 gm. (*0.0017 gm.) of H202; and since 169.6 gms. of H „02 are equivalent to 844.1 gms. . „ / 58a02 SHA \ f.l N of Ba02, (844.x gms. 169.6 gms.J’ * yy perman* ganate solution corresponds to 0.008441 gm. of Ba02. Not less than 40 cc. of the decinormal solution should be required. Thus .008441 X 40 = 0.3376 gm. lOO “ PUle ®a^»* Oxalic Acid, H2C204 + 2H20 | *^6— Oxalic acid may be estimated either by neutralization with an alkaline V. S., or by oxidation with potassium perman- ganate V. S. The permanganate is generally used when the acid is in combination as oxalate. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 159 The reaction is illustrated as follows: S(H2CA + 2H20) + 3H2504 + 2KMn04 100)628.5 100)315.34 6.285 gins. 3.1534 gins, or 1000 cc. permanganate V. S. 10 = K2S04 -f- 2MnS04 -(- i 8H20 + ioC02. N Thus each cc, of the permanganate represents 0.006285 gm. of pure oxalic acid (crystallized). Note.—It must be remembered, in titrating with per- manganate, that an excess of sulphuric acid is always necessary, in order to keep the resulting manganous compound in solution, by forming a soluble manganous sulphate. If hydrochloric acid is used the solution must be very dilute, and the temperature not raised too high, other- wise chlorine will be liberated, which will spoil the analysis. It should be borne in mind that the solution of potassium permanganate should not be filtered through paper, as it is decomposed by organic matter. It may, however, be filtered through gun-cotton or glass-wool. It should never be used in a Mohr’s burette. A TEXT-BOOK OF VOLUMETRIC ANALYSIS, Table of Substances which may be Estimated by Oxidation, by Potassium Dichromate or Potassium Permanganate, showing Formula, Molecular Weight, Factor, etc. Name of Substance. Formula. Mole- cular Wt. — V. s. 10 Used. Factor (exact). hph„o2 65.88 !25 7 zKMn04* .OO1647 .O06285 .OC844T .0021209 OO2O877 •011573 H2C204-f~2]-I20 BaG2 Ca(PH202)2 F e2(PH202)6 FeC03 sKMnOi 169.67 501.04 ns.64 71.84 2KMn04* i K2Cr207 / \ zKMn04 f j K2Cr2G, 1 \ 2KM11O4 i FeO Ferrous sulphate (anhydrous). ... FeS04 151-58 j K2(Jr2Q7 1 1 2KMn04 f .OI5I7O 2FeS04-p3H20 357-28 J K 2(Jr2(J7 ( .017864 1 2K.MnG4 j Ferrous sulphate (crystallized)... FeS04 + yH20 277.42 j K2Cr207 / 1 2KMnG4 ) .027742 Fe2 III.76 j K2Cr207 I 1 2l\Mn04 f .005588 33-92 3i 9a 103 9i 105.84 sKMn04 .OO1696 .OOO798 •5b94 .002598 .002646 Oxygen,wt. of available, in H202 “ volume “ “ “ 02 o2 kph2o2 2KMn04 2KMn04 NaPH202 f-H20 zKMnOj* * Determined by residual titration with decinormal oxalic acid V. S. The factors given in this table are calculated upon the revised atomic weights, which are indorsed by the U. S. P. A TEXT BOOK OF VOLUMETRIC ANALYSIS, CHAPTER XII. ANALYSIS BY INDIRECT OXIDATION. This method of analysis is based upon the oxidizing power of iodine. lodine acts upon the elements of water, forming hydriodic acid with the hydrogen, and liberating oxy- gen in a nascent state. Nascent oxygen is a very active agent, and readily combines with and oxidizes many substances, such as arsenous oxide, sulphurous acid, sulphites, thiosul- phates, etc. As203 + 2H20 2l2 = 4HI + As205; HsS03 -f HaO +I, = 2HI + H,SO4. Therefore iodine is said to be an indirect oxidizer, and may be used for the estimation of a great variety of substances, with extreme accuracy. The end of the reaction in an analysis by this method is ascertained by the use of starch test solution, which produces, with the slightest trace of free iodine, a dis- tinct blue color. In making an analysis with standard iodine solution, the substance under examination is brought into dilute solution, the starch solution added, and then the iodine, in the form of a decinormal solution, is delivered in from a burette, stirring or shaking constantly, until a final 162 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. drop colors the solution blue—a sign that a slight ex- cess of iodine has been added. Decinormal lodine V. S„ I = | | in I litre.—12.653 gms. of pure iodine are dissolved in 300 cc. of distilled water containing 18 gms. of pure potassium iodide. Then enough water is added to make the solution measure, at 150 C. (590 F.), exactly 1000 cc. The solution should be kept in small glass-stoppered vials, in a dark place. The potassium iodide used in this solution acts merely as a solvent for the iodine. If pure iodine be not at hand, it may be prepared from the commercial article as follows ; Powder the iodine and heat it in a porcelain dish placed over a water-bath, stirring constantly with a glass rod for 20 minutes. Any adhering moisture, to- gether with any cyanogen iodide, and most of the iodine bromide and iodine chloride, is thus vaporized. Then triturate the iodine with about 5 per cent, of its weight of pure, dry potassium iodide. The iodine bromide and chloride are thereby decomposed, potas- sium bromide and chloride being formed, and iodine liberated from the potassium iodide. The mixture is then returned to the porcelain dish, covered with a clean glass funnel, and heated on a sand- bath. A pure resublimed iodine is then obtained. If pure iodine is used in making this solution, there is no necessity for checking (standardizing) it. But if desired, the solution may be checked against pure arsenous acid or pure sodium thiosulphate, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 163 ESTIMATION OF ARSENOUS ACID. Arsenous Anhydride, Arsenic Trioxide, As203 = | *l9B^'—When arsenous acid is brought in contact with iodine in the presence of water and an alkali, it is oxidized into arsenic acid, and the iodine is decolorized. The reaction is: As,o. + 21, + 2tt,o = As.O. + 4HI; NaHCO, + HI = Nal + H.O + CO,. The alkali should be in sufficient quantity to combine with the hydriodic acid formed, and must be in the form of potassium or sodium bicarbonate. The hydroxides or carbonates should not be used, as they interfere with the indicator. Starch solution is used as the indicator, a blue color being formed as soon as the arsenous acid is entirely oxidized into arsenic acid. o. 1 gm. of arsenous acid is accurately weighed and dissolved, together with about 1 gm. of sodium bicar- bonate, in 20 cc. of water heated to boiling. Allow the liquid to cool, add a few drops of starch T. S., and allow the decinormal iodine V. S. to flow in, shaking or stir- ring the mixture constantly, until a permanent blue color is produced. The following equation illustrates the reaction ; As A + 5H20 + 21. = 4HI + 2H3AsO 4)197.68 4)506 IQ) 49-42 10)126.5 N 4.942 gms. 12.65 gms. or 1000 cc. ~ lodine V. S. 164 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N Thus it is seen that each cc. of the standard so- -10 lution represents 0.004942 gm. of pure As203. If 20 cc. are consumed, then 0.004942 X 20 = 0.09884 gm. .09884 X 100 o o v = 98.84$ The U. S. P. requirement is 98.8 A. of As303. The starch T, S. is not used in the U. S. P. process, and the end of the reaction is known by the iodine being no longer decolorized. But with starch the indication is exceedingly delicate, and it should always be used. Liquor Acidi Arsenosi, U. S. P.—Measure accu- rately 10 cc. of the solution, add to it 1 gm. of sodium bicarbonate, and boil for a few minutes. Then allow the liquid to cool, and dilute it to 50 cc. with water. A little starch T. S. is then added and the decinormal iodine V. S. run in from a burette, until a final drop produces the blue color of starch iodide. N Each cc. of I. V. S. represents 0.004942 gm. of As203. (See Estimation of Arsenous Acid.) The U. S. P. requirement is that 24.7 cc. of the liquor acidi arsenosi, when treated as above, will con- sume 49.4 to 50 cc. of decinormal iodine V. S. Use 2 gms. of the bicarbonate. q.004942 X 5° = 0.2471 gm. 0.2471 X 100 — = Ifo 24.7 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 165 Liquor Potassii Arsenitis, U. S. P. (Fowler’s Solu- tion).—The process is exactly the same as the fore- going. 24.7 cc., diluted and treated with 2 gms. of sodium bicarbonate, should require 49.4 to 50 cc. of N the I. V. S., corresponding to i/0 of As203. Sulphurous Acid (Acidum Sulphurosum, U. S. P.)— This is an aqueous solution of sulphur dioxide, S02 | Gaining 6.4 per cent., by weight, of the gas. Sulphurous acid when brought in contact with iodine is oxidized into sulphuric, the iodine being decolorized because of its union with the hydrogen of the accom- panying water, forming hydriodic acid. Two gms. of sulphurous acid are taken and diluted with distilled water (recently boiled and cooled) to about 25 cc. The decinormal iodine V. S. is then delivered into the solution (to which a little starch T. S. had been previously added) until a permanent blue color is produced. At least 40 cc. of the standard iodine solution should be consumed before this color appears. The following equations, etc., show the reaction that takes place: H2S03 + Hao + I, = 2HI + H3S04. 2)81.86 2)253 10)40.93 10)126.5 N 4.093 gms. 12.65 gms. or 1000 cc. V. S. 10 N Thus each cc. of the V. S. represents .004093 gm. of pure H2S03. Sulphurous acid being, however, looked upon as a 166 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. solution of S02 in water, the quantity of this gas is generally estimated in analysis. h2o,so2 + Hao + I, = 2HI + h2so4. 2)63-9 2)253 10)31.95 10)126.5 3.195 gms. 12.65 gms. N Thus each cc. of V. S. consumed before the blue 10 color appears represents 0.003195 gm. of S02. If 40 cc. are consumed in the above analysis, the 2 gms. contain 0.003195 X 40 = 0.i278; then 0.1278 X 100 cr. —2 = 6.39i0 of S02. The sulphurous acid should be diluted with distilled water to below 0.04 per cent before titrating it; for if it is not sufficiently diluted there is a risk of the sul- phuric acid formed, being again reduced to sulphurous, with liberation of iodine, thus causing irregular results. This may, however, be obviated by adding at once N . a measured excess of iodine V. S. and titrating back N with sodium thiosulphate V. S. The direction to boil the distilled water is given for the purpose of freeing it from air, which would have a tendency to partially oxidize the sulphurous acid. Sodium Sulphite, Na2S03 -f- 7H20 = | — One gm. of the salt is dissolved in 25 cc. of distilled 167 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. water recently boiled to expel air, a little starch T. S. is added, and then the decinormal iodine V. S. de- livered in from a burette, until the blue color of starch iodide appears, which does not disappear upon shaking or stirring. The reaction is expressed as follows : Na,SO3 + ;H2O + I, = 2NaI + H2S04 + 6HaO. 2)251-58 2)253 10)125.79 10)126.5 N 12.579 gms. 12.65 gms. or 1000 cc. iodine V. S. Thus each cc. of the standard solution represents .012579 gm. of crystallized sodium sulphite. If 1 gm. of the salt is taken, to find the percentage multiply the factor by the number of cc. of standard solution consumed, and the result by 100. The U. S. P. requirement is 96 per cent. 0.63 gm. of salt should require for complete oxidation 48 cc. of the standard solution. Therefore .012579 X 48 = .603792 gm* 0.603792 X 100 063 = Potassium Sulphite, K3S03 -j- 2H30 = *194.— Operate upon 0.5 gm. in the same manner as for sodium sulphite. KaS03 + 2H20 + I, = 2KI + h2so4 + h2o. 2)194 2)253 io) 97 10)126.5 9.7 gms. 12.65 gms. or 1000 cc. of standard V, S. 168 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Each cc. of the decinormal iodine V. S. used rep- resents 0,0097 gm. of crystallized potassium sulphite. If 46 cc. are used, the salt is over 89$ strength. Sodium Bisulphite, NaHSO, = | *;°f6-Dis- solve 0.26 gm. of the salt in 20 cc. of distilled water which has been previously boiled to expel air, add a little starch T. S., and pass in the decinormal iodine V. S. from a burette, until a permanent blue color appears. At least 45 cc. should be required. Apply the following equation NaHS03 + I 2 + HaO = Nal +HI + H2S04. 2)103.86 2)253 10) 51-93 10)126-5 N 5.193 gms. 12.65 gms. or 1000 cc. V. S. Thus each cc. of decinormal iodine V. S. represents 0.005193 gm. of sodium bisulphite. 0.005193 X 45 = 0.23368 gm. 0.23368 X 100 Tie = Sodium Thiosulphate (Sodium Hyposulphite), Na2S203-f 5H20 = | *248 64*—T^is when brought in contact with iodine, is converted into tetrathionate of sodium, and the iodine is decolorized. It is estimated as follows ; 0.25 gm. of the salt is dissolved in 10 cc. of water, a few drops of starch T. S. N . are added, and then the iodine V. S. is delivered in ’ IO from a burette, until the appearance of blue starch iodide indicates an excess of iodine. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 169 At least 9.9 cc. of the standard solution should be added before a final drop produces a permanent blue color. The reaction is expressed as follows 2(NaIS.OI>sH.O) + I. 2)495.28 2)253 10)247.64 10)126.5 24.764 gms. 12.65 gms. or 1000 cc. I. V. S. 2NaI -f- Na2S406 -j- ioHaO. Thus each cc. represents .024764 gm. of crystallized thiosulphate. 9.9 cc. contain 0.024764 gm. X 9-9 = .2451636 gm. 0.2451636 X ioo =98.1% 0.25 * ' lodine may also be used for estimating antimonous compounds. The reaction is similar to that with arsenous compounds ; thus Sb,o, + 2HaO + 2l„ = SbA + 4HI. Antimony and Potassium Tartrate (Tartar Emet- ic), 2(K(SbO)C.H.O.) + H.O = | *66442■ Tliis is the only antimonial salt, a process for the volumetric estimation of which is given in the U. S. P. The U. S. P. directs that o 331 gm. of the crystal- lized salt or 0.322 gm. of the salt dried at no° C. (230° F.) be taken for analysis. The salt is dissolved in 10 cc. of water, and about 20 cc. of a cold saturated solution of sodium bicarbonate and a little starch T. S. added. The decinormal iodine V. S. is then delivered in from a burette, until the blue color of the starch A TEXT-BOOK OF VOLUMETRIC ANALYSIS. iodide makes its appearance, indicating that the salt has been completely oxidized and that the iodine solu- tion has been added in slight excess. Not less than 20 cc. of decinormal iodine V. S. should be consumed before the blue color appears. The reaction is illustrated by the following equa- tion : 2(K(SbO)C.H4O.)+H.Q + 21, + 3H,0 4)662.42 4)506. - 10)165.605 X0)126.5 16.5605 gms. 12.65 gins, or 1000 cc. I.V.S. = 4HI + 2KHC4H406 + 2HSb03. N Thus each cc. of iodine V. S. represents 0.0165605 gm. of pure crystallized tartar emetic. 2(K(SbO)C4H40,) (anhydrous). 4)644.46 io)i6i.iis n 16.X115 gms. = 12.65 gms. of iodine or 1000 cc. V. S. N Thus each cc. of iodine V. S. represents 0.0161115 gm. of anhydrous tartar emetic. Thus 20 cc. = 0.0165605 gm. X 20 = .33121 gm.; 0.33121 X 100 , , , = 100$ crystallized salt; 0.331 and 0.0161115 X 20 = 0.32223 gm. 0.32223 X 100 , , , —— = 100)6 anhydrous salt. 0.322 J A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 171 The operation should be quickly conducted or a Precipitate of antimonous hydrate will be formed, upon which the iodine has little effect. The antimony must be in solution to be properly attacked. Table of Substances Estimated by lodine. Name of Substance. Formula. Molecular Weight. Factor. Antimony and potassium 1 tartrate ) 2(K(Sb0)C4H40,)+H20 AS203 K2S03 + 2H20 NaHSOg Na2S03 -j- 7H20 NaaS403 +sH20 so2 h2so3 662.42 197.68 j93.84 IO3.86 251-58 247.64 63.90 81.86 j Cryst. .016560 | Anhydr. .016111 .004942 .009692 .005Tgs .012579 .024764 .003195 .004093 Sodium bisulphite Sodium thiosulphate 1 (hyposulphite) ) A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XIII. ESTIMATION OF SUBSTANCES READILY REDUCED. Any substance which readily yields oxygen in a defi nite quantity, or is susceptible of an equivalent action, which involves its reduction to a lower quantivalence, may be quantitatively tested, by ascertaining how much of a reducing agent of known power is required by a given quantity of the substance for its complete re- duction. The principal reducing agents which may be em- ployed in volumetric analysis are sodium thiosiLlphate, sulphurous acid, arsenous acid, oxalic acid, metallic zinc, and magnesium. The sodium thiosulphate is the only one which is employed officially in the U. S. P. in the form of a volumetric solution. It is used in the estimation of free iodine, and indirectly of other free halogens, or compounds in which the halogen is easily liberated, as in the hypochlorites, etc. It depends upon the fact that iodine is an indirect oxidizer, as shown by its action upon water, the hydro- gen of which it abstracts, forming hydriodic acid, thus liberating the oxygen in a nascent state. This method of analysis is called lodometry. When sodium thiosulphate acts upon iodine, sodium tetrathionate and sodium iodide are formed, and the solution is decolorized. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 173 This reaction takes place in definite proportions: one molecular weight of the thiosulphate, absorbs one atomic weight of iodine. 2Na2S303 + I 2 = 2NaI -)- Na2S406. Chlorine cannot be directly titrated with the thiosul- phate, but by adding to the solution containing free chlorine an excess of potassium iodide, the iodine is liberated in exact proportion to the quantity of chlorine present, atom for atom. Cl, + 2KI - 2KCI + 1,. Then by estimating the iodine, the quantity of chlorine is ascertained. All bodies which contain available chlorine, or which when treated with hydro- chloric acid evolve chlorine, may be estimated by this method. Also, bodies which contain available oxygen, and which when boiled with hydrochloric acid evolve chlorine, such as manganates, chromates, peroxides, etc., may be estimated in this way. Solutions of ferric salts, when acidulated and boiled with an excess of potassium iodide, liberate iodine in exact proportion to the quantity of ferric iron present. Thus sodium thiosulphate may be used in the esti- mation of a great variety of substances with extreme accuracy. (Hyposulphite), Na2S203 -f- SHaO = | *248 contains *24 | §ms‘ 1 litre.—Sodium thiosulphate is a salt of thiosulphuric acid in which two atoms of hydrogen have been replaced by sodium ; it therefore seems that a Preparation of Decinormal Sodium Thiosluphate A TEXT-BOOK OF VOLUMETRIC ANALYSIS. normal solution of this salt should contain one half the molecular weight in grammes in one litre. But this salt is used chiefly for the estimation of iodine, and, as stated before, one full molecular weight reacts with and decolorizes one atomic weight of io- dine; and since one atom of iodine is chemically equiv- alent to one atom of hydrogen, a full molecular weight of sodium thiosulphate, must be contained in a litre of its normal solution. Sodium thiosulphate is easily obtained in a pure state, and therefore the proper weight of the salt, re- duced to powder and dried between sheets of blotting- paper, maybe dissolved directly in water, and made up to one litre. The U. S. P. directs that a stronger solution than necessary be made, its titer found by iodine, and then the solution diluted to the proper measure. 30 gms. of selected crystals of the salt are dissolved in enough water to make, at or near 150 C. (590 F.) 1100 cc. Transfer 10 cc. of this solution into a flask or beaker, add a few drops of starch T. S., and then gradually deliver into it from a burette decinormal iodine solu- solution, in small portions at a time, shaking the flask after each addition, and regulating the flow to drops toward the end of the operatio.n. As soon as a blue color is produced which does not disappear upon shak- ing, but is not deeper than pale blue, the reaction is completed. Note the number of cc. of iodine solution used, and then dilute the thiosulphate solution so that equal volumes of it and the decinormal iodine V. S. will exactly correspond to each other, under the above- mentioned conditions. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 175 Example.—The 10 cc. of sodium thiosulphate, we will assume, require 10.7 cc. of decinormal iodine V. S. The sodium-thiosulphate solution must then be diluted in the proportion of 10 cc. to 10.7 cc., or 1000 cc. to 1070 cc. After the solution is thus diluted a new trial should be made, in the manner above described, in which 50 cc. of the thiosulphate solution should require exactly 50 cc. of the decinormal iodine V. S. to produce a faint-blue color. The solution should be kept in small dark amber- colored, glass-stoppered bottles, carefully protected from dust and air. One cc. of this solution is the equivalent of: Iodine Bromine .. 0.007976 “ Chlorine .. 0.003537 Iron in ferric salts... . ( 126 X lodine, I = | *J2^''ju•—Dissolve 0.32 gm. of iodine in 20 cc. of water, in a beaker or flask, with the aid of 1 gm. of potassium iodide; the solution is mixed with a few drops of starch T. S., and then the deci- normal sodium thiosulphate V. S, gradually delivered in from a burette, in small portions at a time, shaking the flask after each addition, and regulating the flow to drops toward the end of the reaction, until a final drop just discharges the blue color. Note the number of cc. of decinormal sodium thio- sulphate V. S. consumed, and multiply this number by the factor for iodine. 176 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 2(NasSso3 -f 5H20) +I, = Na2S406 -f 2NaI + ioHsO. 2)496 2)253 10)248 10)126.5 24.8 gms. or 12.65 gms. N 1000 cc, V. S. 10 Thus the factor for iodine, that is, the quantity equiv- N alent to 1 cc. of thiosulphate V. S., is 0.01265 gm. 0.32 gm. of iodine, which answers to the tests of the N U. S. P., requires at least 25 cc. of the V. S. 0.01265 x 25 = 0.31625 gm. .31625 X 100 _ _ . ... = 98.8$ pure iodine, Liquor lodi Compositus (Lugol’s Solution).—This is an aqueous solution of iodine and potassium iodide. It is estimated for iodine in the same way as the foregoing. The potassium iodide acts merely as a sol- vent for free iodine, and does not enter into the re- action. 10 or 12 gms. of the solution is a convenient quan- tity to operate upon. Starch T. S. is the indicator. The U. S. P. states that 12.66 gms. of the solution should require for complete decoloration from 49.3 to 50 cc. of decinormal sodium thiosulphate V. S. N As shown by the above equation, each cc. of the V. S. represents 0.01265 gm. of pure iodine. There- fore 50 cc. represent 0.01265 X 50 = .6325 gm. .6325 X 100 * 5% pure iodine, übout* 12.66 J r A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Tinctura lodi (Tincture of lodine).—This is an al- coholic solution of free iodine, and must be diluted with a solution of potassium iodide, before titration, in order to provide sufficient liquid to keep the resulting salts in solution. Aqua Chlori (Chlorine Water)—This is an aqueous solution of chlorine, Cl = | *25 con^a^n^nS at least 0.4$ of the gas. The estimation of chlorine is effected in an indirect way, namely, by determining the quantity of iodine which it liberates from potassium iodide. A definite quantity of chlorine will liberate a definite quantity of iodine from an iodide ; these quantities are in exact proportion to their atomic weights, as the equation shows: 2KI 4- Cl. = 2KCI + Ia 2)70-74 2)253 10)35.37 10)126.5 3-537 gms. 12.65 gms. Thus it is seen that by estimating the liberated io- dine the quantity of chlorine may be determined with accuracy. Ten gms. is a convenient quantity to operate upon. To this about half a gramme of potassium iodide is added. A little starch T. S. is then introduced, and the titration is begun, with decinormal sodium thiosul- phate V. S. When the blue color of starch iodide has entirely disappeared the reaction is finished. The reaction between iodine and sodium thiosulphate is illustrated by the following equation • 178 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 2)253 2)496 10)126.5 10)248 12.6s gms. 24.8 gms. or 1000 cc. —V. S 10 I, +2(Na2SA + sH,o)=2Nal+Na,Sio6+ioHlo. N Thus we see that 1000 cc. of Na2S203 5H20 repre- sent 12.65 gms. of iodine, which are equivalent to 3.537 gms. of chlorine. Each cc. therefore is equivalent to .003537 gm. of chlorine. This number is the factor which, when mul- N tiplied by the number of cc. of thiosulphate V. S. used, gives the weight in grammes of chlorine, contained in the quantity of chlorine water acted upon. The U. S. P. requirement is that 17.7 gms. of chlorine water, when mixed with 1 gm. of potassium iodide dis- N solved in 10 cc. of water, and titrated with sodium 10 thiosulphate V. S. should consume not less than 20 cc. of the latter in decolorizing the solution. •003537 X 20 = .07074 gm. .07074 X 100 , f . = .04$ of chlorine. 17.7 Chlorinated Lime (Calx Chlorata, Chloride of Lime, Bleaching-powder).—This substance was formerly sup- posed to be a compound of lime and chlorine, CaOCl2, and hence the name chloride of lime. It is now gener- ally considered to be a mixture of calcium chloride and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 179 calcium hypochlorite, CaCl, -j- Ca(ClO), or 2(CaOCI3). The hypochlorite is the active constituent. This is a very unstable salt, and is readily decomposed even by carbonic acid. When treated with hydrochloric acid it gives off chlorine. The value of chlorinated lime as a bleaching or dis- infecting agent depends upon its available chlorine, that is, the chlorine which the hypochlorite yields when treated with an acid. In estimating the available chlorine, the latter is liberated with hydrochloric acid. This liberated gas, then, acting upon potassium iodide, sets free an equiva- lent amount of iodine. The quantity of iodine is then determined, and thus the amount of available chlorine found. .1 to .2 gm. is a convenient quantity to oper- ate upon. The U. S. P. directs to weigh off *0.35 (0.354) gm. of chlorinated lime. This is to be thoroughly triturated with 50 cc. of water and carefully transferred, together with the washings into a flask. 0.8 gm.or more of po- tassium iodide and 5 cc. of diluted hydrochloric acid are then added, and into the resulting reddish-brown liquid, N the sodium thiosulphate V. S. is delivered from a burette. Towards the end of the titration, when the brownish color of the liquid is very faint, a few drops of starch T. S. are added and the titration continued until the bluish or greenish color produced by the starch has entirely disappeared. Not less than 35 cc. of the volumetric solution should be required to pro- duce this result. The reactions which take place in this process are illustrated by the following equations : A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CaCI„Ca(CIO), + 4HCI = 2CaCla + 2HS0 + 2Cla 2CI, + 4KI = 4KCI -f- 2ls. 4)141.48 4)506 IO) 35.37 10)126.5 3-537 gms. 12.65 gms. 2ls + 4(Na,SaOs+sH2o)=4Nal+2Na3S4o6+2oHaO. 40)506 40)496 N 12.65 gms. 24.8 gms. or 1000 cc. thiosulphate V. S. We thus see that 1 cc. of the decinormal volu- metric solution represents 0.01265 gm. of iodine, which is equivalent to 0.003537 gm- °f available chlorine. Then 0.003537 X 35 = 0.12379 gm 0.12379 X 100 . • = 35/» of available chlorine. •35 This is a very rapid method for estimating chlorine ; but when calcium chlorate is present in the bleaching- powder (and it often is, through imperfect manufact- ure) the chlorine from it, is recorded, as well as that from the hypochlorite, the chlorate being decomposed into chlorine, etc., by hydrochloric acid. The chlorate, however,is of no value in bleaching; its chlorine is not available. Hence, unless the powder is known to be free from chlorate, the analysis should be made by means of arsenous-acid solution. The Arsenous-acid Process. 0.35 gm. of the bleaching-powder is rubbed to a smooth paste with 50 cc. of water, as described above. A measured excess of decinormal arsenous acid V. S. is then added ; this A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 181 is followed by a little starch T. S., and then decinormal iodine V. S. added until the blue color appears. De- duct the number of cc. of the standard iodine solution used from those of standard arsenous-acid solution, and the quantity of the latter which went into combi- nation is found. N Each cc. of AsaOs V. S. represents .003537 Sm- °f available chlorine. 2CaOCl2 + As203 = Asa06 -f- 2CaCI, 4)141.48 4)198 10) 35-37 10) 49-5 N 3.537 gms. 4.95 gms. or 1000 cc. V. S. Decinormal Arsenous-acid Solution is made by dissolving 4.95 gms. of the purest sublimed arsenous anhydride (AsaOs) in about 250 cc. of distilled water with the aid of about 20 gms. of pure potassium bicar- bonate. The acid should be in fine powder, and the mixture warmed, to effect complete solution. The solution is checked with decinormal iodine V. S., using starch as indicator. Decinormal arsenous-acid solution and decinormal iodine solution should correspond, volume for volume. Liquor Sodae Chloratae (Solution of Chlorinated Soda; Labarraque’s Solution).—This is an aqueous solution of several chlorine compounds of sodium, principally sodium chloride and hypochlorite, contain- ing at least 2.6f0 of available chlorine. In this solution, as in chlorinated lime, it is the available chlorine which is estimated. The chlorine is first liberated with hydrochloric or sulphuric acid ; this then liberates iodine from potassium iodide, and the 182 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. free iodine is then determined by standard solution of thiosulphate. *6.7 (6.74) gms. of chlorinated soda solution are mixed with 50 cc. of water, 2 gms. of potassium iodide, and 10 cc. of hydrochloric acid, together with a few drops of starch T. S. Then pass into the mixture from a burette sufficient decinormal sodium thiosulphate V. S. to just discharge the blue or greenish tint of the liquid. The reaction is illustrated by the following equation. Hydrochloric acid liberates chlorine from the salts in the solution : NaCI,NaCIO + 2HCI = 2NaCI + HaO + Cl,. 70.74 The chlorine then liberates iodine from potassium iodide; Cla + 2KI = 2KCI + 12.I2. 20)70-74 20)253 3-537 12.65 The iodine is then determined by sodium thiosul- phate V. S.: I, + 2(Na2S2o3+sH2o)=2Nal+Na2S4oB+ioH2o. 2)253 2)496 10)126.5 10)248 N 12.65 gms. 24.8 gms. or 1000 cc. V. S. Thus each cc. of standard solution represents .01265 gm. of iodine, which is equivalent to .063537 gm. of available chlorine. In practice the potassium iodide should always be added before the hydrochloric acid is, so that the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 183 chlorine has potassium iodide to act upon, as soon as it is itself liberated, and thus any loss of chlorine is obviated. In the pharmacopoeial test above given not less than N 50 cc. of the V. S. should be required. 10 0.003537 X 50 = 0.17785 gm. = 2 avai]aWe C 1 6./ Instead of weighing off the U. S. P. quantity, any other convenient weight may be taken. ESTIMATION OF FERRIC SALTS. When a ferric salt in an acidulated solution is di- gested with an excess of potassium iodide the salt is reduced to the ferrous state, and iodine is set free. Fe2Cl6 + 2KCI = 2FeClj + 2KCI + 12.I2. One atom of iodine is liberated for each atom of iron in the ferric state. The liberated iodine is then determined by sodium thiosulphate, in the usual way. 12.65 gms. of iodine = 5.6 gms. of metallic iron. This is the method of the U. S. P. ; it is given in detail here. *0.56 (0.5588) gm. of the salt is dissolved in 10 or 15 cc. of water and 2 cc. of hydrochloric acid in a glass- stoppered bottle having a capacity of about 100 cc. 1 gm. of potassium iodide is then added, and the mix- ture digested for half an hour at a temperature of 40° C. (104° F.). During the digestion the stopper should be 184 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. left in the bottle, and the heat not allowed to rise too high, otherwise the liberated iodine will be volatilized. When cool a few drops of starch T. S. are added. N It is now ready for titrating with - sodium thiosul- -10 phate. Each cc. corresponds to I per cent, of metallic iron. When the quantity of metallic iron and the chemical formula for the ferric salt under estimation are known, the quantity of pure salt is easily found by calculation. In all the estimations of ferric iron it is convenient to take 0.56 gm. of the salt. Each cc. of the volumetric solution used will then represent 1 $ of metallic iron, assuming the atomic weight of iron to be 56. Ferric salts may be tested in many other ways; for instance: A ferric salt in solution may be filtered through a column of zinc dust, which reduces it to the ferrous state. This is then estimated with potassium perman- ganate V. S. in the usual method, or the ferric solution is treated with a few small pieces of zinc or magnesium coarsely powdered, until complete reduction is effected. When a red color is no longer produced by sulphocy- anate of potassium the ferric salt is completely re- duced, and may be estimated with potassium perman- ganate V. S. Stannous chloride, ammonium bisulphite, and other substances may also be used as reducing agents. Ferric Chloride, Fe2CI6 -f- i 2H20 = | #539-s^ (, 5 *0.56 (0.5 588) gm. of the salt is dissolved in a glass- stoppered bottle (having a capacity of about 100 cc.) in 10 cc. of water and 2 cc. of hydrochloric acid, and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 185 after the addition of 1 gm. of potassium iodide, is kept for half an hour at a temperature of 40° C. (104° F.), then cooled, mixed with a few drops of starch T. S., and titrated with decinormal sodium thiosulphate V. S. until the blue or greenish color of the liquid is dis- charged. Each cc. represents *0.0056 gm. or 1 $ of metallic iron, or 0.026975 gm. of pure ferric chloride. The following equations illustrate the reactions; Fe2CI#+i 2 = 2FeCl2+2KCl+ I 2 + I 2H20. V y J 20)539-5 20)253 26.975 gms. 12.65 gms. Then I. + 2(Na25203 + 5H30) 20)253 20)496 N 12.65 gms. 24.S gms. or 1000 cc. V. S. 10 = 2NaI + Na2S406 + ioH20. N 20 cc. of the V. S, should be required, which rep- -10 resents 20$ of metallic iron, or 96.34$ of pure% ferric chloride (crystallized): 0.026975 X 20 = 0.5395 grn. 0*5395 X 100 , =93-34* Liquor Ferri Chloridi (Solution of Ferric Chloride). —This is an aqueous solution of ferric chloride, Fe2Cl6 = | *224 containing about 37.8 per cent, of the an- hydrous salt or about 13 per cent, of metallic iron. 186 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 0.56 (or .5588) gm. of the solution is introduced into a glass-stoppered bottle (having a capacity of about 100 cc.), together with 15 cc. of water and 2 cc. of hydro- chloric acid. 1 gm. of potassium iodide is then added, and the mixture kept for half an hour at 40° C. (104° F.), then cooled, and mixed with a few drops of starch N T. S. and titrated with sodium thiosulphate V. S. 10 until the blue or greenish color of the liquid is dis- charged. 0.56 gm. of the solution having been taken, each cc. of the standard solution represents 1 per cent, and 13 cc. should be required. If 1.12 gms. are taken, as the U. S. P. directs, each cc. represents 0.5 per cent, and 26 cc. should be required. The reactions are the same as in ferric chloride, each cc. representing 0.026975 gm. of crystallized ferric chloride, or 0.016199 gm. of anhydrous ferric chloride, or .0056 gm. of metal- lic iron. To find percentage: Multiply by number of cc. used, then multiply the result by 100 and divide by the quantity of solution taken. Tinctura Ferri Chloridi (Tincture of Ferric Chlo- ride).—A hydro-alcoholic solution of ferric chloride, Fe2Cl6 = | conta^n^ng about 13.6 per cent. of anhydrous ferric chloride, and corresponding to about 4.7 (4.69) per cent, of metallic iron. To estimate this tincture follow the directions given for liquor ferri chloridi. Ferric Citrate,FFa( = | Z^48-—*°-56 (0.5588) gm- the salt is dissolved in a glass-stop- pered bottle (having a capacity of 100 cc.) in 15 cc. of water and 2 cc. of hydrochloric acid, with the aid of gentle heat. 1 gm. of potassium iodide is then added, A TEXT-BOOK Of" VOLUMETRIC ANALYSIS. and the mixture kept for half an hour at a temperature of 40° C. (104° F.). It is then cooled, and a few drops of starch T. S. added. The decinormal sodium thio- sulphate V. S. is then delivered in from a burette, until the blue or greenish color of the liquid just disappears. Each cc. of the decinormal solution represents 1 per cent, or 0.0056 gm. of metallic iron, corresponding to 0.024424 gm. of ferric citrate. 3Fe,(C.H.0,).+6K1 =2Fe.(C.H.0,).+2K,C.H.0,+31, Ferric citrate. Ferrous citrate. ,/ 3Fe2 \488.48 6)759 6)335.28 3 10)126.5 IO) 55-88 6)1465.44 12.65 gms. 5.588 gms. 10) 244.24 (*5.6 gms.) 24.42 24.424 gms I 2 + 2(Na2S2Os, 5H20) = 2NaI-fNa2S4O6 + ioH20. 2)253 2)496 10)126.5 10)248 N 12.65 gms. 24.8 gms. or 1000 cc. sodium thiosulphate. Thus each cc. represents 0.01265 gm. of iodine, which corresponds to 0.024424 gm. of ferric citrate or *0.0056 gm, metallic iron. 16 cc. —l6 X 0.0056 = 0.896 gm. metallic iron. 0.896 x ioo , = 16/ c 0.56 16 X 0.024424 0.390784 gm. ferric citrate. 0.390784 X 100 . , = Liquor Ferri Citratis (Solution of Ferric Citrate). —This is an aqueous solution of ferric citrate, corre- sponding to about 7.5 per cent, of metallic iron. 188 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. *0.56 (0.5588) gm. of the solution is introduced into a glass-stoppered bottle (having a capacity of about 100 cc.), together with 15 cc. of water and 2 cc. of hy- drochloric acid. 1 gm. of potassium iodide is then added, and the mixture kept at a temperature of 40° C. (104° F.) for half an hour ; it is then cooled and mixed with a few drops of starch T. S., and deci- normal thiosulphate V". S. delivered in from a burette until the blue or greenish color of the liquid is dis- charged. Each cc. of the volumetric solution indicates 1/0 of metallic iron. If *1.12 (1.1176) gms, of the liquor are taken, as the U. S, P. directs, each cc. of the V. S. used represents of metallic iron. Iron and Ammonium Citrate (Fend et Ammonii Citras).—The precise chemical constitution of this preparation is not determined. Therefore the metallic iron only is estimated, of which it should contain 16 per cent. Ammonio-ferric Tartrate (Ferri et Ammonii Tar- tras).—The exact chemical composition of this com- pound is not known. It is, theoretically, 2(FeO)- NH4C4H406-3H20). It should contain 17 per cent, of metallic iron. Potassio-ferric Tartrate (Ferri et Potassii Tartras). —There is some difference of opinion as to the com- position of this salt. It is probably a double salt, con- sisting of one molecule of ferric tartrate, Fe2(C4H406)3 and one of potassium tartrate, K2C4H406, with one of H2O. It should contain 15 percent, of metallic iron. Soluble Ferric Phosphate (Ferri Phosphas Solu- bilis).—This salt is called soluble ferric phosphate in order to distinguish it from the true ferric phosphate. It is not a definite chemical compound, but a mixture A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 189 of citrate and phosphate of sodium and iron It should contain 12 per cent of metallic iron. The foregoing four salts being of indefinite chemical composition, are tested for metallic iron only, as follows : 0.56 (0.5588) gm. of the salt is dissolved in a glass- stoppered bottle (having a capacity of 100 cc.) in 15 cc. of water and 2 cc. of hydrochloric acid. 1 gm. of po- tassium iodide is then added, and the mixture kept at 40° C. (104° F.) for half an hour, then cooled, a few drops of starch T. S. added, and decinormal sodium thiosulphate V. S. delivered in slowly from a burette until the blue or greenish color of the liquid is com- N pletely discharged. Each cc. of —V. S. represents 1 per cent, of metallic iron, if 0.56 (0.5588) gm. of the salt is taken. Iron and Quinine Citrate (Ferri et Quininae Cit- ras).—The U. S. P. gives an assay process for quinine and one for iron to be applied to this salt. ESTIMATION OF THE QUININE. 1.12 (1.1176) gms. of the salt are dissolved in a capsule in 20 cc. of water, with the aid of gentle heat. The solution is poured into a separator, the capsule is rinsed with a little water, and the rinsings added to the liquid in the separator ; when this has become cool, add 5 cc. of ammonia water and 10 cc. of chloroform, and shake. Allow the liquids to separate, draw off the chloroformic layer, and add to the residual liquid a second and a third portion of 10 cc. of chloroform added, shaking after each addition, and drawing off the chloroformic solution. The combined chloroformic 190 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. solutions are evaporated spontaneously in a tared cap- sule, and the residue dried at ioo° C. (2120 F.) to a constant weight. It should weigh not less than 0.1288 gm. 0.1288 X 100 , , - . . 1 = 11.5$ of dried quinine. In the above assay the ammonia water precipitates the quinine and the chloroform dissolves it. Then by evaporating the chloroformic solution the quinine is obtained. ESTIMATION OF THE IRON, The aqueous liquid from which the quinine has been removed, as above described, is heated on a water-bath until the odor of chloroform and ammonia has disap- peared; allow the liquid to cool, and dilute it with water to the volume of 50 cc. Take 25 cc. of this, put it in a glass-stoppered bottle (having a capacity of 100 cc.), add 2 cc. of hydrochloric acid and 1 gm. of potassium iodide, and digest at 40° C. (104° F.) for half an hour. Allow it to cool, add a few drops of starch T. S. and titrate with decinormal sodium thiosulphate V. S. until the blue or greenish color is discharged. Each cc. of the volumetric solution represents 0.0056 (.005588) gm, of metallic iron, or 1 per cent. 14.5 cc. should be required. 0.0056 x 14-5 = 0.08i2 gm. 0.0812 x 100 . ^— = 14.5^ Soluble Citrate of Iron and Quinine (Ferri et Quininae Otras Solubilis).—This salt is assayed for A TEXT-BOOK OF VOLUMETRIC ANALYSIS. quinine and iron in the manner above described under Ferri et Quinines Citras, and should respond to the requirements for the latter. Iron and Strychnine Citrate (Ferri et Strychninae Citras).—This salt should be tested quantitatively for strychnine and iron. ESTIMATION OF THE STRYCHNINE. *2.24 (2.2352) gms. of the salt are dissolved in a sep- arator in 15 cc. of water, 5 cc. of ammonia water are then added and 10 cc. of chloroform, and the mixture shaken. Set aside so as to allow the liquids to separate, draw off the chloroformic layer, add a second and a third portion of 10 cc. of chloroform, shaking each time and drawing off the chloroformic solution. The chloroformic extracts are then mixed, and allowed to evaporate spontaneously in a tared capsule. The resi- due is then dried at ioo° C. (2120 F.) to a constant weight. This residue should not weigh less than 0.02 gm. nor more than 0.0224 gm., corresponding to not less than 0.9 nor more than 1 per cent, of strychnine. .0224 X 100 — Iyo 2.24 / ESTIMATION OF THE IRON. The aqueous liquid from which the strychnine has been removed in the manner described above, is heated on a water-bath until the chloroform and ammonia are entirely volatilized. This is then allowed to cool, and diluted with water to the volume of 100 cc. 25 cc. of 192 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. this are transferred to a glass-stoppered bottle (having a capacity of 100 cc.), 2 gms. of hydrochloric acid and 1 gm. of potassium iodide are then added, and the mix- ture kept at a temperature of 40° C. (104° F.) for half an hour. After it has been allowed to cool add a few drops of starch T. S., and titrate with decinormal so- dium thiosulphate V. S. until the blue or greenish color N of the liquid is entirely discharged. 16 cc. of the V. S. should be required to produce this result, each cc. corresponding to 1 per cent, or 0.0056 gm. of metallic iron. 0.0056 x 16 = 0.0896 gm. 0.0896 X 100 , , ct- 2— = ibi, of Fe. 0.56 Ammonio-ferric Sulphate (Ferri et Ammonii Sul- phas ; Ammonio-ferric Alum), Fe2(S04)B.(NH4)2S04 24H20 = | —"phis salt has a definite chemical composition, and therefore by determining the quan- tity of metallic iron the quantity of pure salt may be found by calculation. The U. S. P. process for assay is as follows: 0.56 (0.5588) gm. of the salt is dissolved in a glass- stoppered bottle (having a capacity of 100 cc.) in 15 cc. of water and 2 cc. of hydrochloric acid, 1 gm. of potas- sium iodide is then added, and the mixture kept at a temperature of 40° C. (104° F.) for half an hour. It is then allowed to cool, and mixed with a few drops of starch T. S., and titrated with decinormal sodium thio- sulphate V. S. until the blue or greenish color of the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 193 N liquid is discharged. Not less than 11.6 cc. of the V. S. should be required, each cc. corresponding to 1 per cent, or .0056 gm. of metallic iron, or 0.0482 gm. of the salt. See the following equations: (Fe,) Fe2(S04),(NH4)2S04.24H20 + 2KI 2)112 2)*9&4 10) 56 10) 482 5.6 gms. 48.2 gras. = 2 FeS04+ K2S04 + (NH4)2SO4 + I 2 + 24HsO. 10)126.5 Then I, + 2(NaaS2o3.sH2o)=2Nal+Na3S4o6+ioH2o. 2)253 2)496 10)126.5 10)248 12.65 gms. 24.8 gms. or 1000 cc. V. S. 10 12.65 gms. N Thus it is seen that I cc. of V. S. represents 0.01265 gm. of iodine, and this corresponds to 0.04.82 gm. of ammonio-ferric sulphate, or 0.0056 gm. of metallic iron. 0.0482 X 11.6 = 0.55912 gm 0.55912X100 , . u - XI = 99.8$ of the pure salt. 0.0056 X 11.6 = .06496 gm. .06496 X ioo , , -p, ———P = 11M of Fe. 0.36 194 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Soluble Ferric Pyrophosphate (Ferri Pyrophos- phas Solublilis).—This is estimated according to the U. S. P. in the following manner: 0.56 (0.5588) gm. of the salt is dissolved in a glass- stoppered bottle (having a capacity of 100 cc.) in 10 cc of water, then 10 cc. of hydrochloric acid and subse- quently 40 cc. of water are added. Then 1 gm. of potassium iodide is put into the solution and the tem- perature kept at 40° C. (104° F.) for half an hour. The liquid is then cooled and a few drops of starch T. S. N added, and the sodium thiosulphate V. S. delivered in from a burette, until the blue or greenish color is N completely discharged. Each cc. of the —V. S. repre- sents 1 per cent, or 0.0056 gm. of metallic iron. True ferric pyrophosphate has the chemical compo- sition Fe4(P20T)3 -j- 9H20. The soluble ferric pyro- phosphate of the U. S. P. is a mixture of ferric pyro- phosphate and sodium citrate. The reaction with potassium iodide is expressed as follows: Fe1(PA). + 4KI = 2Fe1PiOl + K4PA + 2l 4)746 4)506 i0)i86.5 10)126.5 18.65 gms. 12.65 gms. Thus 18.65 gms. of ferric pyrophosphate cause the liberation of 12.65 gms. of iodine, and since each cc. of N sodium thiosulphate V. S. will absorb, and con- sequently represent, .01265 gm. of iodine, it corre- sponds to 0.01865 gm. of pure ferric pyrophosphate, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 195 10 cc. of the decinormal solution is the quantity which the U. S. P. requires should be used. 0.01865 X io = 0.1865 gm. 0.1865 X ioo of ferric pyrophosphate, which corresponds to 10$ of metallic iron in the U. S. P. salt. Ferric Valerianate (Ferri Valerianas), Fe2(C6HG02)8 = I*7lB.—The true ferric valerianate is illustrated by the above formula, but the U. S. P. salt is of variable composition, and should contain not less than 15$, nor more than 20$, of iron in combination. The estimation is conducted as follows: *0.56(0.5588) gm. of the salt is dissolved in a glass-stoppered bottle (having a capacity of 100 cc.) in 2 cc. of hydrochloric acid. This decomposes the salt, forming ferric chlo- ride and liberating valerianic acid. 15 cc. of water are now added, together with I gm. of potassium iodide, and the mixture heated to 40° C (104° F.) and kept at that temperature for half an hour; it is then cooled, and the liberated iodine estimated with decinormal sodium thiosulphate V. S., using starch T. S. as indi- cator. N Not less than 15 cc. nor more than 20 cc. of the 10 V. S. should be required to discharge the color of starch iodide. Each cc. corresponds to i^s3_ 17 = I available O = 126.5 O This shows that 126.5 gms. of iodine are liberated by 17 gms. of absolute peroxide, which are equivalent to 8 gms. of available oxygen. N Thus 1000 cc. of sodium thiosulphate V. S., which absorb and consequently represent 12.65 gms. of iodine, are equivalent to 1.7 gms. of H202 or 0.8 gm. of avail- able oxygen. N Each cc. of this ~ V. S., then, represents, of H2Q *0.0017 gm., of available oxygen *O.OOOB gm. The coefficients for weight of H202 and of oxygen, it is seen, are identical with those used in the perman- ganate process. Therefore the coefficient for volume is also the same in this method as in the other, namely, 0-5594- A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 201 The process is carried out as follows: Take 2or 3 cc. of sulphuric acid, dilute it with about 30 cc. of water, add an excess of potassium iodide (about 1 gm.), and then 1 cc. of hydrogen peroxide. After the mixture has been allowed to stand five minutes starch T. S. is added, N and the titration with sodium thiosulphate begun. Note the number of cc. required to discharge the blue color, and multiply this number: by 0.0017 gm. to find the quantity, by weight, of H202; by 0.0008 gm. to find the weight of available oxygen ; by 0.5594 cc. to find the volume of available oxygen. If 18 cc.are required, the solution is of 0.5594 X 18 10.0683 volume strength. 0.0017 x 18 = .0306 or 3.06$ H202. 0.0008 X 18 = .0144 or 1.44$ of oxygen With this method the author has always obtained satisfactory results. The lack of uniformity in the re- action, which is frequently reported, is doubtless due to the use of insufficient acid. Table of Substances, Estimated by Decinormal Sodium Thio- sulphate V. S. Name. Formula. Molecular Weight. Factors. Chlorine Cl2 70.68 Gm. •003537 F erric acetate t* e2(C2 H3U2)b Fe2(Jl6 -f- i2H2G 464.92 .023446 Ferric chloride 539 5 .026975 Ferric citrate P e2(C6H607)2 488.48 .O24424 Ferric nitrate Fe2(N03)6 483.x .O24I5 F'erric phosphate .. Fe2(P04)2 *302 .0151 F'erric pyrophosphate F'e4(P207)3 anhydrous *746 .01865 F'erric sulphate 399.2 .01996 Ferric and ammonium sulphate. F'e2iNH4)2(S04U+24H20 *964.0 .0482 Ferric valerianate Fe2(C5HyG2)6 *718 •0359 Hydrogen peroxide h2o2 33-92 .001696 Iodine 253 .01265 Iron, in ferric salts Fe2 II I .76 .005588 Oxygen, available, weight o2 *32 .0008 Oxygen, available volume o2 *32 •5594 cc. Part 11. CHAPTER XIV. SANITARY ANALYSIS OF WATER. In collecting samples of water great care must be exercised in order to secure a fair representation of the water and to avoid the introduction of foreign matters. The samples should be collected in clean glass-stop- pered bottles having a capacity of from 2 to 5 pints. It is well to completely fill the bottle with water, then empty it, and again fill with the water to be ana- lyzed. In taking samples from lakes, reservoirs, or slow streams the bottle should be submerged, so as to avoid collecting any water that has been in direct contact with the air. In collecting from pump-wells a few gallons should be pumped out before taking the sample in order to remove that which has been standing in the pump. If the public water-supply is to be analyzed, take the water from a hydrant communicating directly with the street main, and not from a cistern. At the time of collecting, a record should be made of those surroundings and conditions which might influ- 202 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. ence the character of the water, such as proximity of cesspools, sewers, stables, and factories. It should also be noted whether the sample is from a deep or shallow well, a river, spring, or artesian well. The nature of the soil and the different strata of the locality must also be taken into account. The sample should be kept in the dark and analyzed with as little delay as possible. Color.—This may be taken by looking down through a column of water in a colorless glass tube about two feet long, standing upon a piece of white paper. A comparison is made with a second tube containing distilled water. Another way of determining the color is by the use of a colorless glass tube two feet long and two inches in diameter, closed at each end, with disks of colorless glass cemented on, but having a small opening at one end for filling and emptying the tube. To use this tube, it is half filled with the water to be examined and placed in a horizontal position. A piece of white paper is held at one end of the tube, and then by looking through from the other end the color of the liquid is and a comparison of tint made be- tween the lower half of the tube containing the water and the upper half containing air. Odor.—Three or four ounces of water are placed in a small flask fitted with a cork through which is passed a thermometer ; the flask is placed in a water-bath and heated to ioo° F. The flask is then shaken, the cork withdrawn, and the odor immediately observed. In this way, satisfactory and uniform tests are ob- tained, and a practised nose can frequently detect pollution. 204 A TEXt-BOOk OF VoLOMETRIC ANALYSIS. Reaction.—This may be determined by the use of a neutral solution of litmus. If an acid reaction is ob- tained, the water should be boiled in order to determine if it is due to carbonic acid; if the red color disappears upon boiling, the acid reaction is due to carbonic acid. Phenolphthalein or lacmoid may also be used for this purpose. Suspended Matter.—A litre of the turbid water is passed through a dried and weighed filter. The filter is then again dried and weighed, and the increase in weight represents the suspended matter in one litre of the water. TOTAL SOLIDS. A platinum dish having a capacity of about 120 cc. is heated to redness, then cooled under a desiccator, and weighed. 100 cc. of the water is then intro- duced and evaporated over a low-temperature burner at a moderate heat. When the residue appears dry the heat may be increased by placing the dish in an air oven kept at a temperature of about 212° F. until it ceases to lose weight; finally cool under a desic- cator, and weigh. In waters of exceptional purity it may be advisable to use larger quantities, such as 250 cc. The increase in weight of the dish represents approxi- mately the total solids contained in the water taken. If the solid residue does not exceed 57 parts per 100,000, no reason is afforded for rejecting the water for domestic use. It has been found that the figure for total solids obtained thus, does not truly represent the sum of the organic and mineral matters in all cases. Experiments have been made with urea dissolved in A TEXT-BOOK OF VOLUMETRIC ANALYSIS. varying quantities of water. Where the solution con- tained i gm. of urea the residue after evaporation varied from c.98 to 0.007 gm- Besides the possible loss of organic matter during the evaporation, some of the mineral constituents may retain with great obstinacy, large quantities of water in the form of water of crystallization, which would cause an error in the opposite direction. Thus the determination of total solids is only an ap- proximation. ORGANIC AND VOLATILE MATTER—LOSS ON IGNITION. Though the mineral matter in a water must to some extent be taken into account in judging of a water, the organic matter is of far greater importance. The really injurious matters are more probably the organic. It is therefore important to determine as near as possible their quantity and nature. It was naturally supposed that by igniting the resi- due obtained from evaporation of the water, the or- ganic matter would be burned out, and that the loss of weight would then represent the organic matter. But as waters ordinarily contain some earthy carbo- nates, which upon ignition are deprived of carbonic-acid gas and converted into oxides, it was customary to add a few drops of carbonic-acid water or ammonium car- bonate to the ash, and then dry and weigh the residue. Ignition, however, decomposes other salts which may be contained in water, and may even volatilize some wholly; therefore the loss on ignition cannot be truly called the organic matter. Hence the expressions “ Or- ganic and Volatile Matter,” and “ Loss on Ignition.” Frankland recommends ignition as a rough qualita- 206 a text-book of volumetric analysis. tive test for the presence of organic matter, the degree of blackening which takes place, giving some idea of the probable amounts of organic matter present. CHLORINE may be estimated by the use of decinormal or centi- normal silver-nitrate solution; but analysts generally use a solution of such strength that I cc. will represent 0.001 gm. of chlorine. Standard Silver-nitrate Solution. Dissolve 4.794 gms. of pure recrystallized silver nitrate in sufficient water to make 1000 cc. Potassium-chromate Solution.—Five gms. of neutral potassium chromate are dissolved in 100 cc. of water and a weak solution of silver nitrate added, drop by drop, until a slight permanent red precipitate is pro- duced, which is allowed to settle in the bottle, or sepa- rated by filtration. The Process.—Measure out 100 cc. of the water to be analyzed into a beaker or white basin ; add a few drops of the potassium-chromate solution ; then run in slowly from a burette, the silver-nitrate solution until a slight red tint appears. Note the number of cc. of silver solution used. Each cc. represents 0.001 gm. (1 milligramme). If the chlorine is present in small quantity, about 250 cc. of the water should be evapo- rated to about one fifth before titrating with the silver-nitrate solution. Example.—loo cc. of water taken, 4 cc. of silver solution consumed ; thus showing that the 100 cc. of water contained 0.004 gm. °f chlorine, or 100,000 cc, contained 4 gms. Multiplied by 10 gives parts per million. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The water must be perfectly neutral before titration. If acid, it must be shaken with a little pure precipi- tated calcium carbonate. AMMONIA. When organic matter decomposes spontaneously, it first forms ammonia, then nitrites, and finally nitrates. Thus the presence of ammonia in water is generally conceded to indicate decomposing organic matter, and hence its determination is an important part of the sanitary examination of water. The ammonia is generally spoken of as free am- monia and albuminoid ammonia, or, more properly, as ammonium salts and ammonia from organic nitrogen. The sanitary examination of a water should always include a quantitative determination of nitrogen in both compounds. The process requires several solutions and consider- able care in manipulation. The solutions required are ; I. Nessler s Solution, made by dissolving 35 gms. of potassium iodide in 100 cc. of water and 17 gms. of mercuric chloride in 300 cc. of water. The liquids may be heated to aid solution, but if so, must be again cooled. When solution is complete, add the latter to the former until a permanent precipitate is pro- duced ; then dilute with a 20% solution of sodium hydroxide to 1000 cc. Now add mercuric-chloride solution again until a permanent precipitate is formed. Let the mixture stand until settled, then decant off the clear solution for use. The bulk of the solution should be kept in a well-stoppered bottle, and a small quantity transferred from time to time to a small bottle, from which it should be used. This solution A TEXT-HOOK OF VOLUMETRIC ANALYSIS* improves on keeping, and reacts with extremely min- ute quantities of ammonia. 2, Sodium-carbonate Solution. A 20% solution of pure freshly-ignited sodium carbonate in water free from ammonia. 3. Standard Ammonium-chloride Solution.—Dissolve 0.3138 (*.314) gm. of pure ammonium chloride in water to 100 cc. For use dilute 1 cc. of this solution with 99 cc. of distilled water free from ammonia. Each cc. of this solution contains 0.00001 gm. of ammonia. 4. Alkaline Potassium-permanganate Solution.—Dis- solve 200 gms. of pure potassium hydroxide and 8 gms. of pure potassium permanganate in sufficient ammonia- free water to make 1000 cc. 5. Ammonia-free Water.—If the distilled water of the laboratory gives a reaction with Nessler’s solution, it should be treated with sodium carbonate, about 1 gm. to the litre, and boiled until one fourth has been evaporated. A good clear hydrant water when treated with so- dium carbonate and distilled yields ammonia-free water. The first portion which comes over has of course some ammonia in it, and small portions of the distil- late should be tested with Nessler’s reagent until no more reaction is obtained ; the remainder, except the very last portion, should be collected. Ammonia-free water may also be obtained by distil- ling water acidulated with sulphuric acid. In the first two processes the ammonia is converted into a volatile salt and is easily dissipated, or appears in the first distil- late ; in the last process it is converted into a non-vol- atile salt, which does not distil over. Apparatus Required,—A still, consisting of a glass A TEXT-BOOK OF VOLUMETRIC ANALYSIS. retort, having a capacity of about 700 cc., which is con- nected with a Liebig’s condenser by an air-tight joint. The heat is applied by means of a low-temperature burner, the iron ring of which is removed, so that the retort rests directly upon the gauze. (See Fig. 25.) Fig. 25. Cylinders for Comparative-color Tests.—These cylin- ders are made of pure colorless glass, about one inch in diameter, having a capacity of about 100 cc. and graduated at 50 cc. These should either have a milk- glass foot, or should stand upon white paper. Two or more of these are required. 210 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The Process.—The retort and condenser are thor- oughly rinsed out with ammonia-free water. Then 500 cc. of the water to be tested are introduced, and about 5 cc. of sodium-carbonate solution added to make the water alkaline. The water is then gently boiled until 50 cc. of distillate are obtained. This distillate is transferred to one of the color-comparison cylinders and 2 cc. of Nessler’s reagent added ; a yellow color is produced, which develops more fully in 3 or 5 minutes, and the intensity of which is proportionate to the amount of ammonia present. The color produced is exactly matched by introduc- ing into another cylinder 50 cc. of ammonia-free water and an accurately measured quantity of the standard ammonium-chloride solution, and 2 cc. of Nessler’s reagent, as before. According as the color so produced is deeper or lighter than that obtained from the water, other solu- tions are prepared for comparison, containing smaller or larger proportions of the ammonium chloride, until the proper color is produced. The distillation is continued, and successive portions of 50 cc. of the distillate taken and tested, until the liquid no longer reacts with Nessler’s reagent. The sum of the figures obtained from the several distillates gives the total ammonia, existing in ammonium com- pounds, in the 500 cc. of water taken. The residue in the retort serves for the determina- tion of the nitrogen of the organic matter, which is converted by the alkaline permanganate into ammonia (albuminoid ammonia). 50 cc. of the alkaline permanganate are placed in a porcelain dish of about 150 cc. capacity, the dish nearly A TEXT-BOOK OF VOLUMETRIC ANALYSTS, filled with distilled water, and then the liquid boiled down to 50 cc. This is added to the residue in the retort, the distil- lation resumed, and the ammonia estimated in each 50 cc. of the distillate, as before described. It is the practice of some analysts to mix the distil- lates of each of the above operations, and thus make determinations merely of the total quantity of ammo- nia and albuminoid ammonia. By so doing valuable information may be lost, since it has been pointed out that the ammonia may be differently distributed in the distillates, according to the state, decomposing or otherwise, in which the ammonia exists in the water. If the ammonia distils over very rapidly, it indicates that the organic matter is in a putrescent or decom- posing condition. If, on the other hand, it distils gradually, it indicates the presence of organic matter in a comparatively stable or fresh condition. It is best, therefore, to keep the record of each distillate, so that the rapidity with which the ammonia is set free, as well as the actual amount, may be known. The greatest care should be exercised in order to avoid the introduction of ammonia in any way during the course of the analysis, since small quantities of ammonia compounds and nitrogenous matters are everywhere present. All measuring-vessels, cylinders, etc., should be thoroughly rinsed before using. NITROGEN AS NITRATES. Solutions Required.—Acid Phenyl Sulphate.—lß.s cc. of strong sulphuric acid are added to 1.5 cc. of 2 12 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. water and 3 gms. of pure phenol. This should be pre- served in a tightly-stoppered bottle. Standard Potassium Nitrate.—o.722 gm. of pure potassium nitrate, previously heated to a temperature just sufficient to fuse it, is dissolved in water, and the solution made up to 1000 cc. 1 cc. of this solution will contain .0001 gm. of nitrogen. The Process.—A measured volume of water is evap- orated just to dryness in a platinum or porcelain dish, 1 cc. of the acid phenyl sulphate added and thoroughly mixed with the residue by means of a glass rod, then 1 cc. of water and three drops of strong sulphuric acid, and the dish gently warmed. ,The liquid is then diluted with about 25 cc. of water, a slight excess of ammonium hydroxide added, and the solution made up to 100 cc. The reactions are: HCiH>S04-f_3HN0I=HCiHt(N01)10+H.S04+2Ha 0 Acid phenyl Trinitrophenol sulphate. (picric acid). HC.H,(N0,).0 +NH.OH = NH.C.H.(NOI).O + H.O. Ammonium picrate. The nitric acid used in the above equation is derived from the potassium nitrate by the action of sulphuric acid. The ammonium picrate imparts a yellow color to the solution, the intenstiy of which is proportional to the amount present. Five cc. of the standard potassium-nitrate solution are now similarly evaporated in a platinum basin, treated as above, and made up to 100 cc. The color produced A TEXT-BOOK OF VOLUMETRIC ANALYSIS. is compared to that given by the water; and one or the other of the two solutions diluted until the tints agree. The comparative volumes of the liquids furnish the necessary data for determining the amount of nitrate present, as the following example will show. Five cc. of the standard nitrate are treated as above, and made up to 100 cc. Each cc. represents 0.0001 gm. of nitrogen. .0001 5 .0005 gm. N per 100 cc. 10 .0050 gm. N per 1000 cc. Suppose 100 cc. of water similarly treated are found to require dilution to 150 cc. before the tint will match that of the standard ; then ioo : 150 :: .005 •x> x 0.0075. That is, the water contains 7.5 milligrams of nitrogen as nitrate per litre. Care should be taken that the same quantity of acid phenyl sulphate is used for the water and for the com- parison liquid, otherwise different tints instead of depths of tints are produced. With river or spring waters 25 to 100 cc. should be evaporated for the test, but with subsoil and other waters which probably contain much nitrates 10 cc. will be sufficient. 214 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The Coppermine Process.—500 cc. of the water are acidulated with oxalic acid, and half of this is poured into each of two wide-mouthed bottles. Into one of these is put a copper-zinc couple, made by taking a piece of sheet zinc (4X6 in.) and rolling it into a loose coil and immersing it in a 1.5-per-cent, solution of copper sulphate until the surface is covered with an even layer of copper. Cork both bottles and let stand 24 hours. Remove 50 cc. from each bottle and Nesslerize as directed under Ammonia. The difference between the two readings gives the ammonia due to the reduction of the nitrates and nitrites present. The nitrogen in the nitrites, which is separately determined, must be subtracted, when the remaining nitrogen will be that from the nitrates. NITROGEN AS NITRITES. Solutions Required.—l. Naphthylammonium Chlo- ride (Naphthalamin Hydrochlorate').—Saturated solu- tion in water free from nitrites. It should be colorless (0.5 gm. dissolved in 100 cc. of boiling water). This solution should be kept in a glass-stoppered bottle with a little animal charcoal, which will keep the solution colorless. 2. Snlphanilic Acid (Para-amido-bcnzene—Sulphonic Acid).—A saturated solution in water free from nitrites (1 gm. in 100 cc. of hot water). Hydrochloric Acid.—2s cc. of concentrated pure hy- drochloric acid mixed with 75 cc. of water free from nitrites. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Standard Sodium Nitrite. 0.275 gm. pure silver nitrite is dissolved in pure water, and a dilute solution of pure sodium chloride added until a precipitate ceases to form. It is then diluted with pure water to 250 cc. and allowed to stand until clear. For use 10 cc. of this solution are diluted to 100 cc. It must be kept dark. One cc. of the dilute solution is equivalent to .00001 gm. of nitrogen. A standard solution of silver nitrite is used by some chemists, but the above is said to give better results. The Process.—100 cc. of the water is placed in one of the color-comparison cylinders, the measuring-vessels and cylinder having previously been rinsed with the water to be tested. By means of a pipette introduce into the water 1 cc. each of the solutions of sulphanilic acid, dilute hydrochloric acid, and naphthylammonium- chloride solution in the order named. It is convenient to have three pipettes—one for each of these solutions, and to use them for no other purpose. In all cases the pipettes should be rinsed with ammonia-free water before using them. Into another clean comparison- cylinder introduce I cc. of the standard nitrite solution and make up to 100 cc. with pure water; then add the same reagents as were added to the water in the other cylinder. A pink color is produced in the presence of nitrites, which requires in dilute solutions half an hour for com- plete development. At the end of that time the darker solution is diluted with water until the tints are matched, and the calculation made as explained under nitrates. The reactions are explained by the following equa- tions : A TEXT-BOOK OF VOLUMETRIC ANALYSIS. C 2H4NH2HSOs 4- HN02 = C 6H4N2S03 + 2H20; Sulphanilic acid. Para-diazo-benzene-sulphonic acid. c6h,n2503 + ClOH7NH3CI Naphthammonium chloride. = ClOH#(NH,)NNC6H4HSO, + HCI. Azo-alpha-amido-naphihalene- parazo-benzene-sulphonic acid. Example.—Suppose that ioo cc. of the water re- quire dilution to 125 cc. in order to bring it to the same tint as that produced by 1 cc. of the standard nitrite solution, which contains .00001 gm. of nitrogen as nitrite. The last-named body gives the color to the liquid. 100 : 125 :: .00001 :x. 0.0000125 gm. in 100. That is, 100 cc. of water contain 0.0000125 gm. of N ; 0.0125 gm. in 100,000 cc. OXYGEN-CONSUMING POWER. Potassium permanganate readily yields up ics oxy- gen, especially in the presence of a strong mineral acid, as sulphuric. It oxidizes many salts, and organic mat- ter. This property led to the idea that this salt may be used for burning up (chemically speaking) the organic matter in water, and that the quantity of permanganate used could be relied upon as a means of measuring the organic matter in water. This method does not distinguish between ani- mal and vegetable matter, nor does the quantity of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. permanganate consumed represent only the organic matter. The organic matters in water are very variable in character and condition, and their oxidability is subject to much difference. Nevertheless as a high oxygen-consuming power certainly indicates pollution by organic matter, the process is of considerable value. The following is a convenient method for approxi- mating the oxygen-consuming power of a water: Solutions Required.—Potassium Permanganate.— 0.395 gm. of pure potassium permanganate is dissolved in distilled water, and the solution made up to 1000 cc. 1 cc. of this solution will yield under favorable circum- stances 0.0001 gm. of oxygen. Diluted Sulphuric Acid.—50 cc. of pure sulphuric acid are mixed with 100 cc. of water, and then just sufficient of the permanganate solution added to give the mixture a faint pink color, which remains after standing in a warm place four hours. The Process.—Five stoppered bottles having a capac- ity of 500 cc. are thoroughly cleansed with strong sul- phuric acid and then carefully rinsed with pure water, and 250 cc. of the water to be tested put into each one. 10 cc. of the dilute sulphuric acid is then added to each, together with regularly increasing quantities of the standard permanganate, say 2, 4, 6, 8, and iocc., respec- tively. At the end of an hour they should be examined, to see which, if any, are decolorized. At the end of the fourth hour they should again be examined, and again at the expiration of twenty-four hours. If all of the bottles are decolorized at or before the 218 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. fourth hour an additional io cc. of the permanganate solution should be added to each bottle. With ordinary waters the first and probably the second bottle will be decolorized, while a little color will remain in the third, and the color in the fourth and fifth will be but little diminished. In this way an ap- proximate figure for the oxygen-consuming power of the water may be obtained, which in most cases is all that is necessary. If a closer figure is desired, the ex- periment may be repeated, using quantities of perman- ganate intermediate between those marking the limits of the reaction. Thus if the second bottle is decolorized and a faint color still remains in the third, repeat the experiment with 5 cc. of the permanganate. This method of procedure has an advantage over some of the other processes, because the rate of oxida- tion can easily be seen. This is considered by some to be of more importance than the actual amount of oxy- gen consumed. It must be remembered that nitrites, ferrous salts, sulphides, etc., consume oxygen as well as organic mat- ter. It is therefore important to boil water containing hydrogen sulphide in order to drive the latter off. Nitrites may be removed by treating the water with sulphuric acid, and boiling. The nitrite is thus con- verted into nitrous acid, which is driven off by the heat. Or the oxygen required to convert the nitrites pres- ent into nitrates may be deducted from the total amount of oxygen consumed. 14 parts of nitrogen as nitrite require 16 parts of oxygen for oxidation into nitrate. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. PHOSPHATES. Solutions Required.—Ammonium Molybdate.—Made by dissolving 10 gms. of molybdic anhydride in a mix- ture of 15 cc. of concentrated ammonia (sp, gr. .900) and 25 cc. of water. This solution is poured slowly, and with constant stirring, into a mixture of 65 cc. of concen- trated nitric acid (sp. gr. 1.4) and 65 cc. of water, and allowed to stand until clear. It should be kept dark. The Process.—One litre of the water is evaporated to about 50 cc.; a few drops of a dilute solution of ferric chloride are added, followed by a slight excess of am- monia. Ferric hydroxide is thus precipitated, which carries down with it all the phosphate. This precipi- tate is separated by filtration, dissolved on the filter in the smallest possible quantity of hot dilute nitric acid, and a little water passed through the filter. The nitrate and washings should not exceed 5 cc., and should, if more, be evaporated to this bulk. The solution is now heated nearly to boiling and 2 cc. of the ammonium-molybdate solution added. If after half an hour an appreciable precipitate is formed, it is collected on a small weighed filter and its weight found after thorough drying. This weight, multiplied by 0.05 gives the amount of P04. If the quantity is too small to be collected and weighed in this manner, it is usually reported as “ traces,” “ heavy traces,” or “ very heavy traces.” HARDNESS. The hardness of water, that is, its soap-destroying power, is due principally to the presence of calcium salts ; but salts of magnesium, iron, and other metals may also contribute to this effect. 220 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Two kinds of hardness are recognized : I. “Temporary,” which is due to the presence in water of the acid carbonates of calcium, magnesium, ■etc. By boiling, these salts are decomposed, the car- bonic-acid gas being driven off, and the neutral carbon- ate formed, which is precipitated. Thus the water loses its hardness upon boiling. CaH2(C03)2 = CaC03 +,H2O + CO, 2. “ Permanent ” hardness is due to the presence in water of salts of the above-mentioned metals which are not removed by boiling, such as the sulphates. Hardness is estimated by means of a standard soap solution. Many samples of water possess both temporary and permanent hardness, and it is sometimes desirable to estimate them separately. The total hardness is estimated in one sample, and the hardness in another sample is determined after boiling and filtering off the precipitated calcium car- bonate. The hardness found after boiling is the permanent hardness, and is the most objectionable form. The difference between the total and permanent hardness is the temporary hardness. To express the hardness in some tangible form, the usual custom in this coun- try and in England is to give results in the correspond- ing amounts of calcium carbonate, i.e., practically to determine the amount of soap destroyed by a meas- ured quantity of water, and then to state the results as the amount of calcium carbonate which would de- stroy that quantity of soap. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The reaction which takes place when soap is added to a hard water, is illustrated in the following equa- tions : CaH,(CO.). + 2NaC1,H..0. Acid calcium Sodium stearate carbonate. (Soap). = Ca(C..H,A), + Na,CO, + H.O + CO,; Calcium stearate. or, CaSO. + 2NaC„H„O, = Ca(C,.H.A). + Na.SO.. Calcium sulphate. The calcium stearate, which is an insoluble calcium soap, is precipitated in both cases as a white curd-like mass. The method for estimating hardness in water by the use of soap solution is known as Clark’s method. Solutions Required.—Standard Soap Solution.— Dissolve 10 gms. of shavings of air dried Castile soap in a litre of dilute alcohol. Filter the solution if it is not clear, and keep it in a tightly-stoppered bottle. Standard Calcium Chloride Solution.—Dissolve i gm. of pure calcium carbonate in the smallest excess of hydrochloric acid, then carefully neutralize with am- monia water, and add sufficient water to make up to one litre. One cc. of this solution will contain the equivalent of o.ooi gm. of calcium carbonate. This solution is used for determining the strength of the soap solution, which is done as follows: Measure out 10 cc. of this solution, add 90 cc. of dis- tilled water, and run in the soap solution, drop by drop, from a burette until a lather is formed, which remains 222 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. for five minutes. Note the number of cc. of soap so- lution used. We now repeat the experiment with 100 cc. of dis- tilled water. The amount of the soap solution re- quired to produce a permanent lather with the distilled water must be deducted from the amount used in the first test. Usually it will be about one half or one cc. The io cc. of the calcium chloride solution contained the equivalent of o.oio gm. of CaCOs. Suppose in the above-mentioned test 8.5 cc. of the soap solution were used to produce a permanent lather, and 0.5 cc. were used by the distilled water. Then 8 cc. were used to precipitate 0.010 gm. of CaC03. Thus each cc. of this soap solution will represent •§■ of .010 gm. .00125 of calcium carbonate. The soap solution may either be used as it is, or it may be diluted with dilute alcohol so that about 10.5 or 11 cc. of it will be required to produce a permanent lather with 10 cc. of the standard calcium chloride so- lution. If so diluted each cc. will represent 0.001 gm. of CaC03. This is a convenient strength, because if 100 cc. of water are operated upon, each cc. of the soap solution used will represent 1 part of CaC03 in 100,000 parts of water. Measure 100 cc. of the water into a well-stoppered bottle having a capacity of about 250 or 300 cc. Add the soap solution gradually from a burette, one cc. at a time at first, and smaller quantities towards the end of the operation, shaking well after each addition until a soft lather is obtained, which if the bottle is placed at rest on its side, remains continuous over the whole surface for five minutes. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 223 The soap should not be added in large quantities at a time, even if the volume required is approximately known. If magnesium salts are present, a kind of scum (simulating a lather) will be seen before the reaction is completed. The character of this scum must be care- fully watched, and the soap solution added very care- fully, with an increased amount of shaking after each addition. The point when the false lather due to the magnesium salt ceases and the true persistent lather is produced is comparatively easy to distinguish. If more than 23 cc. of the soap solution are con- sumed by the 100 cc. of water, a smaller quantity of water should be taken (say 50 or 25 cc.) and made up to 100 cc. with distilled water, recently boiled. In such case the quantity of soap solution used must be multiplied by 2 or 4. If the first-mentioned soap solution is used each cc. represents 0.00125 gm. If the second solution is used each cc. represents 0.001 gm. of CaC03, and if 100 cc. of water are acted upon each cc. represents 1 part of CaCO, in 100,000. If 70 cc. of water are acted upon, instead of 100 cc., each cc. of soap solution used represents 1 gm. per 70,000 cc., which corresponds to I gr. per imperial gallon (70,000 grs.) or 1 degree of hardness. These estimations are, however, only approximate, for the lather does not form until the reaction between the soap and the calcium in the water is completed, and then the quantity of soap solution required to produce the lather depends upon its strength. Dr. Clark, the originator of this method, has shown that 1000 grains of distilled water (free from hardness) 224 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. require 1.4 measures of soap solution, each measure being the volume of 10 grains of distilled water at 160 C. For Permanent Hardness.—To determine the hard- ness after boiling, a measured quantity of water must be boiled briskly for half an hour, adding distilled water from time to time to make up the loss by evaporation. At the end of the half-hour allow the water to cool, make up to its original volume with recently boiled and cooled distilled water, filter rapidly, and test in the same manner as described above. One half or one cc. is de- ducted from the soap solution used, for the calculation. Among German chemists it is customary to desig- nate the soap-destroying power equivalent to 1 part of CaO in 100,000, as one degree of hardness. Among French chemists each degree of hardness represents 1 part of CaC03 in 100,000. INTERPRETATION OF RESULTS. Statement of Analysis.—The composition of water is generally expressed in terms of a unit of weight in a definite volume of liquid, but no fixed standard is used, the proportions being expressed by some analysts in parts per million, by others in parts per hundred thou- sand. Sometimes, generally by English chemists, the figures are given in grains per imperial gallon of 70,000 grains; less frequently, in grains per U. S. gallon of 58,328 grains. In order to pass judgment upon the analytical re- sults from a sample of water, the analyst must know to which class of water it belongs—whether river-water, well-water, or artesian-well water. He must know something of the soil and geological character of the locality from which the water is obtained, as well as A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 225 other conditions of the locality which might affect the quality of the water, such as proximity of stables, cess- pools, sewers, factories, etc. Color.—Water of the highest purity is clear, color less, odorless, and nearly tasteless. But the color of water is no indication of its quality. A turbid or col- ored water is not necessarily a dangerous one, neither is a clear, colorless water always a safe water. Odor.—For comfort, if for nothing else, potable water should be free from odor. Water sometimes has an unpleasant odor and taste, yet it may be used with perfect safety for domestic purposes. At other times the odor may give rise to suspicions which a subsequent examination may confirm. Thus by the odor alone the safety of the water cannot be told. Total Solids.—This is intended to represent the total solid matters dissolved in the water; but since much of the organic matter as well as some of the in- organic matter is volatilized by evaporation, the total solids obtained by this method are only the total non- volatile solids. The indication is thus lower than it should be. On the other hand, certain salts, especially calcium sulphate, retain water of crystallization, thus producing an effect in the opposite direction. The total solids so obtained, contain both organic and inorganic matters, either of which may be injurious or not. Mineral waters contain large quantities of in- organic salts. Much smaller quantities of total solids in other waters might indicate pollution. Large quantities of mineral solids, especially of marked physiological action, are known to render water non-potable; but no absolute maximum or minimum can be assigned as the limit of safety. An arbitrary 226 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. limit has, however, been fixed by sanitary authorities of 60 parts per ioo;ooo ; and if the solid residue does not exceed 57 parts per 100,000, there is no reason for rejecting a water. Many waters, especially artesian waters, which are in constant use, contain much larger quantities. The loss on ignition should never reach 50 per cent of the total residue. Chlorine in potable waters is very largely derived from sodium and potassium chlorides of urine and sewage. Food contains considerable amounts of chlorides, and still more is added by way of condiment in the shape of salt. The chlorine thus taken into the system is again thrown off in the excreta, and thus ap- pears in the sewage ; hence the presence of large quan- tities of chlorine in water is taken as an indication of pollution. Urine contains about 500 parts of chlorine per 100,000. The average quantity found in sewage is about 11.5 parts per 100,000. Over 5 parts per 100,000 of chlorine in a water may be considered, in most cases, to be due to pollution of the water by sewage or animal excretions. The chlorine itself is not a dan- gerous constituent of water, but its presence in large quantities is an unfavorable indication. Nevertheless too much dependence must not be put upon the amount of chlorine in water as a means of judging of its purity, for dangerous vegetable matter may exist in it without its presence being indicated by chlorine. The maximum amount of chlorine per 100,000, given by the Rivers Pollution Commission, is 21.5 parts, the minimum 6.5 parts. Various conditions, however, which affect the proportion of chlorine, such as the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. nature of the strata through which the water passes, proximity to the sea, etc., must be taken into account. Nitrogen in Ammonia.—Ammonium compounds are usually the result of the spontaneous putrefactive fermentation of nitrogenous organic matter; nitrites are then formed, and finally nitrates. Ammonium com- pounds may also result from the reduction of nitrites and nitrates in the presence of excess of organic matter. Therefore in either case the presence of ammonia sug- gests contamination. This fact is so generally conceded that the estima- tion of ammonia in water, is a very important part of the sanitary examination. In the water from deep wells an excess of ammonia is nearly always found, but its presence here cannot always be considered an adverse condition, since it is derived largely from the decomposition of nitrates, and shows previous contamination ; but the water hav- ing undergone extensive filtration and oxidation, its organic matter is presumably converted into harmless bodies. Rain-water often contains large proportions of am- monium compounds, which it dissolves out of the air in its descent; but here also, this fact cannot condemn the water, since it does not indicate contamination with dangerous organic matter. An average of 71 samples of rain-water collected in England contained 0.05 parts per 100,000, including an exceptional maximum of 0.21 parts. Fischer (“ Chemische Technologic des Wassers”) gives two analyses of typically good wells, containing respectively 0.048 and 0.044 Parts Per 100,000, and of 228 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. two typically bad shallow wells, containing respec- tively 0.084 and 2.227 parts per 100,000. Albuminoid Ammonia.—If water yields no albu- minoid ammonia it is free from recently added organic contamination. If it contain more than 0.01 part per 100,000 it is looked upon as suspicious, and when it reaches 0.015 parts per 100,000 it is to be condemned. When free ammonia is present in considerable quan- tity, then the albuminoid ammonia becomes suspicious when it reaches 0.005 parts per 100,000. An opinion should not, however, be formulated without a knowl- edge of the source of the water; for, as has been said before, free ammonia may exist in large quantities in deep wells without indicating contamination. Wanklyn gives the following standards: High purity 000 to .0041 of albuminoid ammonia per 100,000 Satisfactory purity .0041 to .0082 “ “ “ . “ “ Impure over .0082 “ “ “ “ “ In the absence of free ammonia he does not condemn a water unless the albuminoid ammonia exceeds .0082 parts per 100,000; but he condemns a water yielding 0.0123 parts of albuminoid ammonia, under all circum- stances. Nitrogen as Nitrates.—Nitrates are normally pres- ent in all natural waters, and are derived chiefly from the oxidation of animal matters. The nitrogen of organic matters liberated by putrefaction, is first converted into ammonia; then this is oxidized into nitrous, and finally into nitric acid. These changes are due partially to direct oxidation and partially to certain micro- organisms which have the power of converting nitro- genous organic matter into nitrites and nitrates. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Nitrates arid nitrites in themselves, in the quantity in which they exist in water, are perfectly harmless. They are, however, an indication of previous contamination ; and many analysts believe that a water which has once been contaminated is always open to suspicion. Others consider them of little importance in determin- ing the impurity of a water. Water which is laden with organic matter is purified by percolating through the ground, the nitrogenous matter being converted into nitrates ; therefore deep wells may contain large quantities of nitrates without being essentially impure, while the water from shallow wells should be con- demned if the nitrates are excessive. Certain strata, as the chalk formation, yield large amounts of nitrates to water. If the nitrogen as nitrates exceeds 0.6 parts per 100,000 the water is suspected. Nitrogen as Nitrites,—Some chemists regard the presence of nitrites as an indication that the oxidation of the dangerous compounds has probably been in- complete, and accordingly condemn water in which nitrites are found. Leeds places the nitrites in Ameri- can rivers at .03 per 100,000. The average in good waters is placed at about .0014 per 100,000. When the quantity exceeds .02 parts per 100,000 it is con- sidered an indication of previous contamination. Oxygen Consuming Power.—This is intended to represent the oxidizable organic matter in the water. But there are other substances in water besides organic matters which absorb oxygen, namely, nitrites, which are thus oxidized to nitrates; ferrous salts, which are oxidized into ferric salts ; etc. Thus the oxygen-con- suming power does not represent the organic matter 230 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. alone. However, a water having a high oxygen-con- suming power may be considered as polluted. The following basis for interpreting results of this method are given by Frankland and Tidy: Oxgen absoibed in 3 hours. High organic purity .05 parts per 100,000 Medium purity 05 to .15 “ “ “ Doubtful 15 to .21 “ “ “ Impure over .21 “ “ “ Phosphates.—Sewage contains large amounts of phosphates, but water usually contains alkaline or earthy carbonates, which precipitate the phosphates ; therefore the absence of phosphates does not indicate purity. But their presence may indicate sewage con- tamination. .06 parts per 100,000 is regarded with sus- picion (calculated as P04). Hardness.—On account of the presence of con- siderable amounts of calcium compounds in our food sewage is usually very hard, containing especially calcium sulphate. The hardness of water, therefore, has some bearing upon the question as to whether the water is probably polluted with sewage or not. But water may be hard, yet otherwise perfectly pure. The test for the degree of hardness is therefore of little importance in determining sewage, as the figures below show that water uncontaminated by sewage may be very hard. Temporary. Permanent. Rain-water, average 0.3 1.7 Highest from different geological formations ... 38.6 48.5 From 272 samples of water from shallow and polluted wells : Minimum o 3.8 Maximum 52 164.3 Average 19 31.5 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 231 The above figures are parts in 100,000. The hard- ness has, however, much significance from an economic point of view. Hard water is objectionable for domes- tic purposes in washing, because of its soap-destroying power, and for manufacturing purposes in boilers. It has no bad effect upon the health, but is by some con- sidered wholesome. Standards.—Certain standards have been fixed by some chemists for determining the purity or impurity of water, according to which if certain figures are ex- ceeded the water is to be condemned. Dr. Tidy's classification depends upon the amount of oxygen consumed, from potassium permanganate, after standing three hours. 1. Great organic purity... ...... o to 0.05 2. Medium purity 0.05 “0.15 3. Doubtful. 0.15 “0.21 4. Impure over 0.21 These standards are applied to waters other than upland surface-waters, in which larger quantities of oxygen may be absorbed. Wanklyris standard is based upon the indications of the amounts of free and albuminoid ammonia, as follows; 1. Extraordinary purity o to 0.005 part albuminoid NH3. 2. Satisfactory purity 0.005100.010 “ “ “ 3. Dirty over 0.010 “ “ If the albuminoid ammonia exceeds 0.005 parts per 100,000 the free ammonia must be taken into account. If the free ammonia is in large quantity it is a sus- picious sign. If it is in small quantity or altogether absent, the water should not be condemned, unless the 232 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. albuminoid ammonia is something like 0.010 parts per 100,000; while over 0,015 should condemn the water absolutely. The following is a list of analyses of waters which were pronounced good. The results are given in parts per 100.000. I. II, III. IV. Chlorine 0.877 i-333 9.294 1-578 Free ammonia 0.0004 none 0.002 0.0002 Albuminoid ammonia none 0.0006 0.005 0.0022 Oxygen absorbed (in 3 hours) 0.0054 0.0016 0.0255 0.0008 N in nitrates and nitrites.... 0.2525 0.3376 0.0107 0.2633 Total hardness 19-23 14.0000 13-33 2.079 Permanent hardness 3-715 3-934 3.060 1.980 Organic and volatile matters i-5 1-7 trace 2. too Total solids (dried at 230" F.) 24.4 27 37-40 9.40 The following were pronounced bad : I. II. III. IV. Chlorine 0.316 62.43 4.208 28.230 Free ammonia 0.0196 0.278 none 0.0105 Albuminoid ammonia 0.0678 0.0030 0.0105 0.0395 Oxygen absorbed (in 3 hours) 0.2912 0.133 0.0165 0.2110 N in nitrates and nitrites.... 0.0283 none 0.247 0.6210 Total hardness 6.940 27.72 13.008 50.00 Permanent hardness 3-5 23.76 2.574 32.670 Organic and volatile matters 0.5 19-5 trace 8.00 Total solids (dried at 230° F.) 15.60 156.20 30.50 146.50 I, Back of slaughter-house ; 11, Drive-well on beach ; 111, Well; IV, Well 30 feet deep. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 233 CHAPTER XV. ESTIMATION OF CARBONIC-ACID GAS IN THE ATMOSPHERE. THIS is done by Pettenkofer’s method. A glass globe or bottle holding from 5 to 10 litres is filled with the air to be tested, by means of a bellows ; baryta water of known strength is then introduced in con- venient quantity. The bottle is then securely closed and set aside for about one hour, rotating it at intervals, so that the liquid is spread over the entire inner wall of the bottle. When the time is up the baryta water is emptied out quickly into a beaker, covered carefully with a watch- glass, and when the barium carbonate has subsided a portion of the clear liquid is withdrawn and titrated N with oxalic-acid solution. The difference between the quantity of oxalic-acid solution required to neu- tralize the barium-hydroxide solution, before and after contact with the air, is the quantity equivalent to the carbonic-acid gas absorbed. The Baryta-water is made by dissolving about 7 gms. of pure crystallized barium hydroxide in 1000 cc. of distilled water. This solution, being prone to absorb C02 out of the air, must be kept in a special bottle, such as is illus- trated in Fig. 23, which prevents access of CO,2 and 234 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. admits of the withdrawal of any quantity of solution without inverting the bottle. The Bottle which is used to collect the air should hold from 5 to 10 litres, and its exact capacity must be known. This may be found by filling the bottle to the bottom of the cork with water and then accurately measuring the water. Before using the bottle it must be absolutely dry. The Analysis.—lnto the bottle, the capacity of which is exactly known,—we will assume it to be 7100 cc.,— is blown the air to be tested, by means of a bellows. 100 cc. of the baryta-water are then introduced, thus leaving 7000 cc. of air in the bottle. The bottle is now securely closed and set aside for about half an hour, rotating it occasionally so as to spread the liquid over the entire inner wall of the bottle. While waiting for the half-hour to expire, a convenient quantity of baryta-water is taken and its strength compared to decinormal oxalic-acid solution by titrating with the latter, using phenolphthalein as indicator. 50 cc. of baryta-water is a convenient quantity. This is placed in a beaker, a few drops of phenolphtha- N lein added, and then titrated with the acid solution 10 until the color just disappears. Let us assume that 40 cc. of the latter were con- sumed ; 80 cc. will then be consumed by 100 cc. of baryta-water. Ba(OH)2 + H2C204 + 2H20 = BaC204 + 4H20 ; 2)170.9 2)126 10) 85.45 10) 63 N 8.545 gms. 6.3 gtns. or 1000 cc. V. S. A TEXT-BOOK OE VOLUMETRIC ANALYSIS. 235 Ba(OH), + CO, = BaCOs+ HaO. 2)170-9 2)44 10) 85.45 10)22 8.545 gms. 2.2 gms. These equations show that 2.2 gms. of carbon di- oxide will neutralize as much barium hydroxide as N 1000 cc. of oxalic-acid solution. And thus each cc. 10 of the oxalic-acid solution is chemically equivalent 10 to 0.0022 gm. of carbon dioxide ; therefore 100 cc. of the baryta-water is capable of absorbing 80 X .0022 gin. = 0.176 gm. of CO, The next step is to determine the quantity of CO, that was absorbed by the 100 cc. of baryta-water, which was introduced into the bottle of air. The liquid is poured out of the bottle into a small beaker, carefully covered with a watch-glass, and the barium carbonate allowed to settle. Then 50 cc. of the clear supernatant liquid are drawn out of the beaker by means of a pipette, treated with a few drops of N phenolphthalein T. S., and titrated with the oxalic acid V. S. until the red color is just discharged. Note the number of cc. consumed, double it, and deduct this number from 80, the quantity which 100 cc. of baryta- water consumed before being brought in contact with CO,, Example.—Assuming that 30 cc. of the oxalic-acid solution were required by the 50 cc. of the baryta- water after exposure, the 100 cc. then would require 60. There is thus a loss of alkalinity equivalent to 20 236 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. N cc. of oxalic acid V. S. This is due to the absorp- -10 tion of carbon dioxide, which neutralizes the hydroxide by forming a carbonate. N Now since each cc. of oxalic acid V. S. is chemi- -10 cally equivalent to 0.0022 gm. of CO,, the baryta- water must have absorbed 20 x 0.0022 gm. = 0.044 gm- °f C03. Therefore the 7000 cc. of air which the bottle held contained 0.044 gm- °f CO,. In stating the result of an analysis the quantity of CO, by volume in 10,000 cc. of air is generally given. In the above case 7000 cc. of air contained 0.044 gm- of CO,; 10,000 cc. of this same air, then, contains 0.044 X io,ooo 0.044 X io , „ or = 0.0628 gm. 7000 7 53 If several bottles are in use it is convenient to mark upon them the multiplier and divisor; thus; 10,000 IO — or —. 7000 7 In calculating the volume of a gas, the temperature and pressure must be taken into account. By referring to the following table the volume occu- pied by 0.001 gm. of CO, at different temperatures can be seen. The volume of 0.0628 gm. of CO, at 160 C. is 0.0628 x 0.53843 o • 33.81 cc. 0.001 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 237 Table showing Volume of .ooi Gm. of Carbon Dioxide at Various Temperatures. c,° F.° Cc. C.° F.° Cc. o 32 0.50863 13 55-4 o.533’4 I 33-S 0.51049 14 57-2 o.5347i 2 35-6 0.51235 15 59 0.53657 3 37-4 0.51451 16 60.8 0.53843 4 39-2 0.51608 17 62.6 0.54030 5 4i 0.51794 18 64.4 0.54216 6 42.8 0.51980 !9 66.2 0.54402 7 44.6 0.52167 20 68 0.54589 8 46.4 0.52353 21 6g. 8 0-54775 9 4S .2 0.52539 22 71.6 0.54961 IO 50 0.52726 23 73-4 o.55i77 ii 51-8 0.52912 24 75-2 0-55334 12 53-6 0.53098 If the pressure remains constant, the volume of a gas increases regularly as the temperature increases, and decreases as the temperature decreases. (Charles’ Law.) This expansion or contraction amounts to of the volume of the gas for each degree centigrade. Thus by calculation the volume of .001 gm. C02 (0.50863 cc.) at any temperature may be found. •gJ-3 Of .50863 = 0.001863. Then to find the volume at any given C. temperature multiply the degree of temperature by 0.001863, and add the answer to 0.50863. 238 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XVI. ESTIMATION OF ALCOHOL IN TINCTURES AND BEVERAGES. The quantity of alcohol contained in dilute spirit, which leaves no residue upon evaporation, may be ascertained by taking the sp. gr. and referring to the alcohol table. When taking the specific gravity, the temperature of the liquid should be 15-|° C. (6o° F.). In Wines, Beer, Tinctures, and other alcoholic liquids containing vegetable matter, the sp. gr. of the sample is taken at 15-!° C. (6o° F.) and noted. A cer- tain quantity (say 100 cc.) is measured off and evapo- rated to one half, or till all odor of alcohol has passed off, the evaporation being conducted without ebullition, in order that particles of the material may not be car- ried off by the steam. The liquid left is then diluted with distilled water, cooled to 6o° F. and made up to the original volume (100 cc.), and the sp. gr. taken. Lastly, we calculate: the sp. gr. before evaporating is divided by the sp. gr. after evaporating, and the quo- tient will be the sp. gr. of the water and alcohol only of the liquor. Then by referring to the alcohol table the percentage of alcohol contained in the liquor is obtained. Example.—The liquor before evaporating had a sp. gr. of 0.9951 ; after evaporation and dilution to 100 cc. the sp. gr. was found to be 1.0081. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 239 ■——— = 0.987, the sp. gr. of the contained spirit. Then by referring to the table we will find that this sp. gr. corresponds to 7.33 per cent., by weight, of abso- lute alcohol. Another Way is to boil the liquid in a retort, con- dense the vapor, and when all the alcohol has passed over add sufficient water to the distillate to make up the original volume, at the temperature of C. (6o° F.). Then, by taking the sp. gr. of this diluted distillate, the quantity of absolute alcohol is found by reference to the table. This latter method requires the taking of the sp. gr. but once and gives more ac- curate results. 240 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Table for Ascertaining the Percentages respectively of Alcohol by Weight, by Volume, and as Proof Spirit, from the Specific Gravity, Condensed from the excellent Alcohol Tables of Mr. Hehner in the “Analystvol. v. //. 43-63, Specific Gravity *5-5°- Absolute Alcohol by w’ght. Per cent. Absolute Alcohol by Vol’me Per cent Proof Spirit. Per cent. Specific Gravity i5-5°- Absolute Alcohol by w’ght. Per cent. Absolute Alcohol by vol’me Per cent. Proof, Spirit. Per cent. ] .oooo 0.00 0.00 0*00 .9489 35-os 41.90 73-43 ■9999 0.05 0.07 0.12 •9479 35-55 42-4S 74-39 .9989 0.58 o-73 1.28 .9469 36.06 43.01 75-37 ■9979 1.12 1.42 2.48 •9459 36.61 43-63 76-45 .9969 1-7S 2.20 3-85 •9449 37-17 44.24 77 53 •9959 2-33 2.93 5-13 •9439 37-72 44.86 78 f 1 •9949 2.89 3.62 6-34 ■9429 38.28 45-42 79 68 •9939 3-47 4-34 7.61 •9419 38-83 46.08 80.75 .9929 4.06 5.08 8.90 .9409 39 35 46 64 81 74 .9919 4.69 5-86 10.26 •9399 39-85 47.18 82.69 •99°9 5.31 6.63 11.62 •9389 40-35 47.72 83 64 .9899 5-94 7.40 12.97 •9379 40.85 48.26 84.58 .9889 6.64 8.27 14.50 •9369 41-35 48.80 85-53 .9879 7-33 9-13 15-99 •9359 41.85 49-34 86.47 .9869 8.00 9-95 17-43 •9349 42.33 49.86 87-37 •9859 B.JI 10.82 18.96 •9339 42.8l 5°-37 88.26 .9849 9-43 11.70 20.50 •9329 43-29 50.87 89.15 •98.39 10.15 12.58 22.06 •9319 43.76 51-38 90.03 .9829 10.92 13-52 23.70 •9309 44 23 Si-8? 90.89 .9819 11 69 14.46 25-34 •9299 44.68 52-34 91-73 .9809 12.46 15.40 26.99 .9289 45-14 52.82 92.56 •9799 13-23 16.33 28.62 .9279 45-59 53-29 93 39 .9789 14.00 17.26 30.26 .9269 46-05 53-77 94-22 •9779 14.91 18.36 32.19 •9259 46.50 54-24 95-05 .9769 15-75 19-39 33-96 •9249 46.96 54-71 95-88 •9759 16.54 20.33 35-63 •9239 47-41 55-18 96.70 •9749 17-33 21.29 37-30 .9229 47.86 S5-65 97.52 ■9739 18.15 22 27 39-°3 •9219 48.32 56.11 98 34 .9729 18.92 23.19 4O.64 .9209 48.77 56.58 99.16 .9719 19-75 24.18 42.38 •9199 49.20 57.02 99-93 .9709 .9699 .9689 20.58 21.38 22.15 25-17 26.13 27.04 44.12 45-79 47-39 •9198 49.24 57.06 ioo.ooPs .9679 22.92 27-95 .9669 23.69 28.86 50.57 .9189 49.68 57-49 TOO.76 .9659 24.46 29.76 52.16 •9179 SO.13 57-97 101.59 .9649 25.21 30 63 53-71 .9169 50.57 58.41 IO2.35 .9639 25-93 3r.48 55-i8 •9159 51.00 58-85 IO3.I2 .9629 26.60 32.27 56-55 .9149 51.42 59-26 103-85 ,9619 27.29 33-o6 57-94 .9139 51-83 59-68 104,58 .9609 28.00 33-89 59-40 .9129 52.27 60.12 i°S-35 •9599 28.62 34-6i 6066 ■9”9 52.73 60.56 106.15 •9589 29-27 35-35 61.95 9109 53-17 61.02 10693 • 9579 29 93 36.12 63.30 •9099 53,61 61.45 107.69 •9569 30-50 36.76 64.43 .9089 54-05 61.88 108.45 ■9559 31.06 37-41 65SS .9079 54-52 62.36 109.28 •9549 31.69 38.11 66.80 .9069 55-oo 62.84 TIO.I2 •9539 32.31 38.82 68.04 .9059 55-45 63.28 IIO.92 ■9529 32-94 39-54 69.29 •9049 55-91 63-73 III.71 •9519 33-53 40.20 70.46 •9039 56.36 64.18 112.49 •9509 34.ro 40.84 71-58 .9029 56.82 64.63 113.26 •9499 34-57 41-37 72.50 .9019 S7-2S 65-05 113-99 A TEXT-BOOK OF VOLUMETRIC ANALYSIS 241 Specific Gravity "S-S0- Absolute Alcohol by w'ght. Per cent. Absolute Alcohol by vol’me Per cent. Proof Spirit. Per cent. Specific Gravity I5-5°- Absolute Alcohol by w’ght. Per cent. Absolute Alcohol by vol’me Per cent. Proof Spirit. Per cent .9009 57-67 65-4S 114 69 .8429 82.19 87.27 152.95 .8999 58.09 65 85 115.41 .8419 82.58 87.58 153 48 .8989 58-55 66 29 116.18 .8409 82.96 87.88 154 ot .8979 59 00 66.74 116.96 • 8399 83-35 88.19 154-54 .8969 59-43 67 T5 117.68 .8389 83-73 88.49 '55-07 •8959 59-87 67-57 118.41 • 8379 84.12 88 7Q 'j5 61 .8949 60.29 67.97 119 12 .8369 84 52 8y 11 150.16 •8939 60 71 68.36 119.80 -8359 84 )2 89.42 156.71 .8929 61.13 68.76 120.49 -8349 85 31 89.72 157-24 .8919 6i.54 69.15 121.18 •8339 85.69 90.02 157-76 .8909 61.96 69-54 121.86 .8329 86.08 90.32 158 28 .8899 62.41 69.96 122.61 .8319 86.46 90.61 158 79 .8889 62.86 70.40 123.36 .8309 86 85 90.90 I59-3I .8879 63-3° 70.81 124. OQ ,8299 87 23 91.20 159.82 .8869 63-74 71.22 124.80 8289 87 62 9r-49 160.33 .8859 64.17 71.62 125.51 .8279 88 00 91.78 160.84 .8849 64.61 72 02 126.22 .8269 88.40 92.08 161.37 .8839 65.04 72.42 126.92 .8259 88.80 92-39 161.91 .8829 65.46 72.80 I27-59 .8249 89.19 92.68 162.43 .8819 65.88 73->9 128.25 .8239 89.58 92-97 162.93 •B8og 66.30 73-57 128.94 .8229 89.96 93.26 i63-43 •8799 66,74 73-97 129.64 .8219 90.32 93-52 163.88 .8789 67.17 74-37 1.30-33 .8209 90.68 93-77 164.33 .8779 67.58 74-74 130.98 .8199 91.04 94 03 164.78 .8769 68.00 75-12 131 64 .8189 91-39 94.28 165.23 •8759 68.42 75 49 132 30 .8179 9r-75 94-53 165.67 .8749 68.83 7S-87 I 32.05 .8169 92.II 94-79 l66.I2 .8739 69.25 76.24 133.60 ■8159 92 48 95-°6 166.58 .8729 69.67 76.61 134-25 .8149 92.85 95-32 167.O4 .8719 70.08 76.08 i34 90 8139 93.22 9S-58 167.50 .8709 70.48 77 32 I35-5I .8129 93-59 95-84 167.96 •8699 70.88 77 67 136-13 .8119 93 96 96.II l68.24 .8689 71.29 78 04 136 76 .8l09 94-31 96-34 168.84 .8679 71.7l 78.40 137 40 .8099 94.66 96.57 169.24 .8669 72.13 78.77 tjS.os . 8089 95-oo 96.80 169.65 .8659 72-57 79.16 138.72 .8079 95-36 97-05 170.07 • 8649 73.00 79-54 '39 39 .8069 95-71 97.29 170.50 .8639 7342 79.90 I40 02 .8059 96.07 97-53 170.99 .8629 73-83 SO 26 I4° 65 .8049 96.46 97-75 171.30 .8619 74.27 80.64 141 33 .8039 96.73 97.96 171.68 .8609 74-73 81.04 142,03 .8029 97.07 98.18 172.05 •8599 75 >8 81.44 14273 8019 97.40 98 39 172-4! •8589 75.64 8l .84 M3 42 .80'19 97-73 98.61 172.80 •8579 76 08 82.23 144. IO 7999 98 06 98 82 ■73-'7 .8569 76.5O 82.58 144 72 .7989 98.37 99 00 173-50 •8559 76.92 82.93 145 34 •7979 98.69 99.18 173.84 •8549 77-33 83.28 145.96 .7969 99 00 99 37 174.17 •8539 77-75 83.64 146-57 •7959 99- 32 99-57 I74-S2 .8529 78.16 83.98 I47-I7 -7949 99-65 99-77 174.87 .8519 78.56 84.31 T47-75 • 7939 99 97 99.98 175.22 .8509 78.96 84.64 148.32 •8499 79-36 84.97 148.90 .8489 .8479 79.76 80.17 85.29 85-63 149.44 150.06 Absolute Alcohol. • 8469 80.58 8S-97 150.67 •8459 8l.OO 86.32 151.27 .8449 81.40 86.64 151-83 I75-2S •8439 8l.80 86.96 152-40 ■7938 100.00 100.00 242 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XVII. ESTIMATION OF TANNIN. G. Fleury (Jour. Phar. Churn., 1892, 499) proposes to use egg-albumen for estimating tannin in wine and in the petals of red roses. The hard-boiled egg-albumen is dried at a moderate temperature, and powdered. This is washed with dilute alcohol (10 per cent), very slightly acidulated with tartaric acid, to saturate the alkali. The albumen is again dried, and kept in a well-stoppered bottle. The method of operation is as follows : Albumen powder, equal to seven or eight times the quantity of tannin, which is supposed to be present, is added to the liquid in a flat dish. The dish is then set aside for forty-eight hours, stirring occasionally; the liquid must during this time be acid, not alkaline. The end of the reaction is attained when the liquid ceases to give a color with ferric chloride T. S. The powder is then collected on a filter, washed with very dilute alcohol, and then dried at ioo° C. At the same time a sample of the original powder is dried and weighed, to determine the amount of water it contains. The increase in weight of the albumen which was in contact with the tannin, minus the loss of weight of the albumen in the check experiment, gives the weight of tannin present. This method is not available for determining the A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 243 tannid in nutgalls, because the absorption by the albu- men is incomplete and too slow. In testing, it must be borne in mind that gallic acid is not absorbed by the albumen, and consequently still gives its reaction with ferric chloride. ESTIMATION OF TANNIN IN BARKS, ETC. (lowenthal’s METHOD.) The principle of this method depends upon the oxi- dation of the tannic acid, together with other easily oxidizable substances, by titrating with potassium per- manganate. The total amount of such substances is thus found, and expressed by a known volume of permanganate. The actual available tannin is then removed by gela- tine or glue, and another titration made, to determine the amount of oxidizable matters other than tannin. The difference between the amounts of permanga- nate solution used in the two titrations gives the amount of tannin present which is available for tan- ning purposes, expressed in terms of permanganate. N Solutions Required.—I. Potassium Permanga- nate VS. (1.05 gm. per litre). 2. Indigo Solution.—6 gms. of pure precipitated in- digo and 50 cc. of concentrated sulphuric acid are dis- solved in sufficient water to make one litre. 3. Glue and Salt Solution.—2s gms. of good trans- parent glue are macerated in cold water, and then heated to dissolve ; the solution is then made up to one litre, and saturated with common salt. The solu- tion should be filtered clear when used. 244 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 4. Acidified Solution of Common Salt.—This is a sat- urated solution of common salt, containing in one litre 25 cc. of sulphuric acid. The Analysis.—20 gms, of the bark or 10 gms. of sumach are boiled with several portions of water until exhausted, and the solution when cold is made up to one litre. 10 cc. of this solution are diluted to 1000 cc.; 25 cc. of the indigo solution are added, and the perman- ganate solution then run in, drop by drop, from a burette, stirring constantly, until the blue color changes to yellow, and the number of cc. of permanganate so- lution consumed noted. 25 cc. of the indigo solution are now taken and di- luted to 1000 cc., titrated with permanganate, and the number of cc. again noted. By deducting this number from the number of cc. used in the first titration, the quantity of permanganate required by the tannin and the other oxidizable substances in the iocc. of solution taken is found. The next step is to deprive a portion of the tannin solution of its tannin, and again titrate. 100 cc. of the tannin solution are treated with 50 cc. of the glue and salt solution, and, after stirring, 100 cc. of the acidulated salt solution are added, the mix ture stirred again, and set aside for several hours. The glue absorbs the tannin out @f solution. The solution is then filtered. The filtrate should be perfectly clear. Of this filtrate take 50 cc. (containing 20 cc. of the tannin solution), mix with 25 cc. of the indigo solution, and titrate with the permanganate solution as before, noting the number of cc. consumed. Another 25 cc. of the indi-go solution are now taken, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 245 diluted as in the other trial, and again titrated with permanganate. By deducting the number of cc. so obtained from the number required by the 50 cc. of filtrate, the quantity required by the oxidizable matter other than tannic acid in the 20 cc. of tannin solution is obtained. Therefore one half of this quantity, when deducted from the quantity of permanganate solution representing the total oxidizable matter in 10 cc. of the tannin solution, gives the quantity of permanganate which was effected by the tannin above. Duplicate titrations should always be made, and should agree within o. 1 or 0.2 cc. of the permanganate solution. Thus far we have only the tannin value (expressed in terms of permanganate), of 10 cc. of the original solution, representing of the material under examination. The permanganate solution may be compared with a standard solution of the purest gallo-tannic acid ob- tainable, or with any tannin of known value, and thus a coefficient obtained. According to the experiments of Neubauer, 63 gms. of pure crystallized oxalic acid (equivalent to 31.4 gms. potassium permanganate) correspond to 41.57 gms. of purified gallo-tannic acid (nutgall tannin). And Oser found that 63 gms. of oxalic acid correspond to 62.355 gms. of querci-tannic acid (oak-bark tannin). These coefficients are now largely used. N Based upon these figures each cc. of permanga- nate solution represents .0013856 gm. of gallo-tannin, or .0020785 gm. of querci tannin. In most analyses, however, especially when the composition of the tannin is not exactly known, it is expressed as oxalic acid. 246 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XVIII. ESTIMATION OF OLEIC ACID. OLEIC acid may be estimated volumetrically by standard solution of potassa or soda, using phenol- phthalein as an indicator. The reaction is expressed by the following equa- tion ; clBh3a + KOH = kc18h330, + HA Oleic acid. N 282 gms. 56 gms. or 1000 cc. KOH, Thus each cc. of the normal alkali solution consumed represents 0.282 gm. of oleic acid. Estimation of Oleic Acid.—-One gramme of the im- pure fatty acid is saponified in a basin by heating with a slight excess of alcoholic potash, till dissolved, and then diluted with water. This solution is treated with acetic acid drop by drop, until on stirring a faint per- manent turbidity ensues. Dilute solution of potassium hydrate is then stirred in drop by drop till the liquid just clears up, and then solution of plumbic acetate is stirred in until precipitation ceases. The precipitate having been allowed to settle, the supernatant liquor is poured off and the soap washed once with boiling water. A little clean sand is rubbed up with the soap in the basin, and the whole scraped out and transferred to a “ Soxhlet,” in which it is thoroughly exhausted with 90 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 247 cc. of pure ether. The ethereal solution (which now contains only plumbic oleate, the plumbic palmitate and stearate being left insoluble in the Soxhlet) is trans- ferred to a special apparatus, sold by apparatus vendors as “ Muter’s oleine tube.” This is a graduated and stoppered tube holding 120 cc., and having a spout and stop-cock at 30 cc. from its base. Previously to intro- ducing the ether, place 20 cc. of dilute hydrochloric acid (1 in 3) into the tube, and then make up the whole with ether-rinsings of the basin to the 120-cc. mark. Close the tube, shake well, and set aside. When settled, note the full volume of the ethereal solution of oleic acid, and run off an aliquot part from the tap into a weighed dish, evaporate, dry in the water-oven, and weigh. Finally calculate this weight to that of the whole bulk of ethereal solution previously noted, thus getting the amount of real oleic acid present in the gramme of crude acid started with. [From Muter’s “ Analytical Chemistry.”] 248 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XIX. ANALYSIS OF SOAP. (a) 10 gms. of the soap are dried to a constant weight at ioo° C. and carefully weighed ; the loss of weight = water. Estimation of Water and Volatile Matters.— (b) Free Fats.—The dried soap obtained as above, is exhausted with petroleum ether of low boiling-point. The petroleum ether is then evaporated off and the residue weighed : this is the weight of the fat contained in 10 gm. of the soap. (c) Fatty Acids.—The residue from (b) which is free from fat and which represents 10 gms. of the soap, is weighed and half of it dissolved in water. Normal nitric acid is then added in excess to liberate the fatty acids. These are collected on a tared filter, dried and weighed. This weight when doubled gives the amount of fatty acids in 10 gms. of the soap. The reaction is illustrated by this equation : NaC18H3A + HN03 = HC18H3302 + NaNO, Sodium oleate. Oleic acid,, The acid filtrate is now titrated with normal soda or potash, using phenolphthalein as an indicator. The difference between the volumes of acid and alkali solu- tions used gives roughly the quantity of total alkali. (d) Chlorides and Sulphates.—The residual neutral A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 249 liquid from the above, is divided into two equal parts, N in one of which chlorine is estimated by“AgNOa, using potassium chromate. In the other sulphuric acid is estimated with barium chloride. (e) Free Alkali, (i.e., the alkali which does not exist as soap).—Ten grammes of the soap are dissolved in hot al- cohol, and one drop of phenolphthalein T.S. added; then carbonic-acid gas is passed through the solution until the color disappears. The free alkali is thus converted into sodium carbonate, which is insoluble in alcohol and may be separated by filtration. The residue on the filter is washed with hot alcohol, and then dissolved •N in a little water and titrated with - acid in the pres- -10 r ence of methyl-orange. The number of cc. used multi- plied by 0.0031 gives the grammes of free alkali, as Na20, in the 10 gms. of soap. Combined Alkali.—The alcoholic solution from the above which contains the combined alkali and the fatty acids, is diluted with a little water, methyl-orange added, and the mixture titrated with decinormal acid. The quantity of combined alkali is thus found. The num- ber of cc. of acid consumed multiplied by 0.0031 gives the quantity as NaaO. Another Way is to evaporate the alcoholic solution to dryness, the residue then ignited, and the soap thus converted into alkali carbonate. This is dissolved in water and titrated with normal or decinormal acid in the presence of methyl-orange. The fatty acids are found by using the factor 0.0282 or 0.282. The number of cc. of decinormal acid used 250 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. in the above titration when multiplied by 0.0282, or of normal acid when multiplied by 0.282, gives the quan- tity of fatty acid as oleic. Soaps, however, contain var- ious fatty acids the molecular weights of which differ. Therefore in estimating the fatty acids volumet- rically, the neutralizing power of the acids liberated from soap, expressed in cc. of standard alkali and called the saponification equivalent, is employed. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XX. DETERMINATION OF THE MELTING-POINT OF FATS. The melting-point of a fat can be quickly found by immersing the bulb of a thermometer in the melted fat, then suspending the bulb which is coated with con- gealed fat in the middle of a beaker of water to which heat is gradually applied, and noting the temperature at which the fatty coat melts from the bulb. Another Way.—Draw out a long capillary tube, Fig. 26. Melt the fat, and draw~a small portion of it up into the tube. The melted fat will rise in the tube by capillary attraction. This tube is bound or held against the bulb of a thermometer, and im- mersed in a beaker of cold water to whith heat is applied. The fat is congealed upon immer- sion in water and becomes opaque. When the temperature of the water is raised to the proper degree, the opaque cylinder of fat melts and be- comes transparent. At this point the tempera- ture must be noted. The congealing-point may be found by removing the source of heat and Fig. 26. allowing the water to cool gradually, and noting the point at which the fat in the tube again congeals and becomes opaque. The congealing may be hastened by adding cautiously cold water to that in the beaker. The congealing-point will be identical with, or close to the melting-point. 252 A TEXT-BOOK OE VOLUMETRIC ANALYSIS. CHAPTER XXL ESTIMATION OF OIL OR FAT IN EMULSIONS AND OINTMENTS. Apparatus.—A test-tube of about eight inches in length, fitted with two good corks, one of which is provided with a wash-bottle arrange- ment, Fig. 27. The Process.—A weighed quantity of the emulsion (2 to 5 gms.) or ointment (1 to 2 gms.) is put into the test-tube, the latter half filled with ether, corked and shaken for about 5 minutes, and set aside so as to allow the liquids to separate. The ethereal solution of the fat or oil, which forms the upper layer, is carefully drawn off into a tared ves- sel. This is done by inserting the stopper having the wash-bottle arrange ment, and gently blowing in the tube a. The tube b is raised or lowered so that its lower end is slightly above the surface of the lower layer in the tube. Fig. 27. This process is repeated until the fat is completely extracted, which is shown by there being no residue left, when a few drops of the last portion drawn off are evaporated on a watch-glass. A TEXT-BOOK OF VOLUMETRIC ANALYSIS 253 The mixed ethereal solutions are now subjected to evaporation, thus leaving the oil behind. The tared evaporating- dish containing the oil is dried in a water-bath and weighed. By deducting the weight of the dish when empty from the above weight, the weight of the fat or oil is obtained. In this way the fat in powdered drugs, in chocolate, in milk, etc., maybe estimated. The estimation is more rapid than though not as accu- rate as, when made by the Soxhlet’s extraction apparatus which is illus- trated in Fig. 28. Into the tarred flask A the ether or other solvent is put. The substance B, inclosed in a cartridge of filtering-paper, is introduced into the tube C. The latter in turn is connected with an upright condenser D. The flask is now heated by a water-bath, and the vapor of the ether rises through £, condenses and drops onto the powdered substance in the cartridge. When the instrument has become filled by the solvent to the level of the top of F, it runs back into the flask charged with part of the soluble matter. This process re- peats itself until the whole of the Fig. 28. soluble matter of the substance has been extracted. 254 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The flask is then detached, and the ether evapo- rated or distilled off; the soluble matter of the origi- nal powder being left in the flask. Resinous or sticky substances should be mixed with a little clean sand, in order to facilitate the extraction and prevent clogging up of the apparatus. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 255 CHAPTER XXII. ESTIMATION OF STARCH IN CEREALS, ETC. The method about to be described depends upon the fact that when barium hydroxide is brought in contact with starch, an insoluble compound is formed, the formula of which is C34PI40O20BaO. This combina- tion takes place in definite proportions, so that if an excess of barium hydroxide solution is added to the starchy substance, and then the excess estimated, the quantity which combined with and which consequently represents the amount of starch present, is found. Solutions Required.— i. Decinormal Hydrochloric Acid. See page 40 (3.637 gm. to 1 liter.) Each cc. represents .00765 gm. of BaO. 2. Baryta-water (barium hydroxide solution), made by dissolving about 7 gms. of pure crystallized barium hydroxide in 1000 cc. of water. Should be kept in a special vessel such as is illustrated in Fig. 23. The Process.—The sample is finely powdered, and 1 gm. weighed out for analysis. This is rubbed up with successive portions of water (using not more than 50 cc.) and transferred to a flask having a capacity of about 150 cc. The flask and contents are now heated upon a water-bath for half an hour to thoroughly gelatinize the starch. If the substance analyzed con- tains oil, this must first be extracted in a “ Soxhlet apparatus before the water is added. 256 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. If free starch is to be experimented with, 0.2 or 0.3 gm. instead of 1 gm. should be taken. When the starch is gelatinized, the solution is cooled, and 25 cc. of the baryta-water are added. The flask is corked, and well shaken for two minutes; proof spirit is then added to make about 125 cc., the flask again corked, thoroughly shaken, and set aside to settle. While settling a check is made upon 10 cc. of the baryta-water mixed with 50 cc. of recently boiled dis- tilled water, by titrating with decinormal hydrochloric acid, using phenolphtalein as indicator. The number N of cc. of hydrochloric acid V. S. used, is noted, and 10 when multiplied by 2\ the total strength of the 25 cc. of the baryta-water employed in the analysis is ob- tained. When the settling of the insoluble compound is completed, 25 cc. of the clear liquid is drawn off (this is ■£- of the entire quantity) with a pipette and rapidly N titrated with the acid V. S. in the presence of a few 10 drops of phenolphtalein T. S. The number of cc. consumed is noted, multiplied by 5, and then deducted from the number representing the total strength of 25 cc. baryta-water. The difference is the quantity which went into combination with the starch. N Each cc. of the hydrochloric acid V. S. represents 0.00765 gm. of Ba02, which is equivalent to 0.0324 gm. of starch. Therefore by multiplying the number of cc. repre- senting the quantity of baryta which combined with A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 257 the starch by 0.0324 gm., the quantity of starch pres- ent in the sample is obtained. Example.—l gm. of substance was taken, mixed with So cc. of water, 25 cc. of baryta-water, and sufficient proof spirit to make 125 cc. This is set aside and allowed to settle. The reaction which takes place is as follows : 2C„H„0,0 + 8a0.H.0 = C„ H..0„,Ha0 + H.O. Starch. '——' 2)648 2)153.0 324 76.5 While settling, the strength of the baryta-water is determined by titrating with decinormal hydrochloric acid V. S., the following equation being applied : BaO,H 20 + 2HCI = BaCl3 + 2H20. 2)72.74 10) 76.5 10)36-37 N 7.65 gms. 3.67 gms. or 1000 cc. V. S. Thus each cc. represents 0.00765 gm. of BaO. 10 cc. of the baryta-water are taken, and 8 cc. of the N acid solution are required to neutralize this. There- fore 25 cc. of baryta-water will require 2\ X 8 cc. = 20 cc. of acid V. S. 10 When the settling is completed, 25 cc. of the clear N solution is drawn off and titrated with acid V. S. 10 N We will assume that 2.5 cc. of the acid V. S. are J 10 258 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. required ; therefore the entire quantity of solution will neutralize 5 X 2.5 cc. = 12.5 cc. The difference between 12.5 cc. and 20 cc. = 7.5 cc., N which is the loss of alkalinity expressed in cc. of N acid V. S. Each cc. of alkalinity lost, expressed as acid V. S., indicates that 0.00765 gm. of BaO went into combination with starch; and since 0.00765 gm. of BaO represents 0.0324 gm. of* starch, the substance analyzed contains 7.5 X 0.0324 gm. or 0.243 gm. of starch. 0.243 X ioo . — = 24.3$ Another Method for Estimating Starch consists in converting it into glucose and then estimating the glucose with Fehling’s Solution. The starch is weighed and boiled in a flask with water containing hydrochloric acid for several hours ; the solution is then cooled, neutralized with potassium hydroxide, and diluted so that I part of starch, or rather sugar, shall be contained in 200 parts of water. This is put into a burette and titrated into 10 cc. of Fehling’s Solution, as described below under Sugar. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XXIII. ESTIMATION OF SUGARS. Fehling’s Solution.—(a) The Copper Solution.— 34-64 gms. of carefully selected small crystals of pure cupric sulphate are dissolved in sufficient water to make, at or near I5°C. (590 F.), exactly 500 cc. Keep in small well-stoppered bottles. (b) The Alkaline-tartrate Solution.—l 73 gms. of po- tassium and sodium tartrate (Rochelle salt) and 125 gms. of potassium hydroxide, U. S. P., are dissolved in sufficient water to make, at or near 150 C. (590 F.), ex- actly 500 cc. Keep in small rubber-stoppered bottles. For use, equal quantities of the two solutions should be mixed at the time required. 10 cc. of the mixed solution is equivalent to Glucose 050 Maltose Inverted cane-sugar 0475 Inverted starch 045 The Process.—0.5 gm, or less of the sugar is dis- solved in 100 cc. of water. This liquid is placed in a burette. 10 cc. of the Fehling’s Solution are mixed with 50 cc. of water and placed in a porcelain dish over a Bunsen burner and heated to boiling. The sugar solution is then run in from the burette, until all blue color is destroyed. 260 a text-book of volumetric analysis. It is always somewhat difficult to determine the exact point at which the blue color disappears, owing to the presence of the precipitated suboxide of copper. This difficulty may be overcome by the addition of some substance which will prevent the precipitation of the cuprous oxide, such as ammonium hydroxide or potassium ferrocyanide. The disappearance of the blue color can then be readily seen, as the solution re- mains clear to the end, turning from blue to green, and finally brown, which indicates the end of the reaction. Professor Bartley reports this method as accurate, reliable, and rapid, provided the solution be not boiled during the reduction. He recommends to add to the Fehling’s Solution in the porcelain basin 10 cc. of a 10$ freshly prepared solution of potassium ferrocy- anide and 30 cc. of water. The ferrocyanide does not precipitate the copper in alkaline solution. If the sugar to be examined be either glucose, malt- ose, or lactose, it may be titrated directly; but if it be cane-sugar, it must first be inverted. This is done by dissolving the sugar (0.475 gin.) in about 100 cc. of water, adding 3 or 4 drops of strong hydrochloric acid, and boiling briskly for ten or fifteen minutes. This is then allowed to cool, neutralized with potassium hy- droxide, and made up to 100 cc. with water. The Calculation.—10 cc. of Fehling’s Solution are always taken ; and whatever the quantity of glucose or sugar solution is required to effect reduction, that quantity contains the equivalent of 10 cc. of Fehling’s Solution. Thus if 12 cc. of the sugar solution were required to reduce 10 cc. of Fehling’s Solution, the 12 cc. contain 0.05 gm. of glucose or 0.082 gm. of maltose, A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 261 etc. 100 cc. of the solution therefore contain x gm. of glucose. 0.5 X 100 . , = 0.416 gm. glucose. 12 The sugar in urine may be estimated by this process. The urine is placed in the burette and run into the boiling Fehling’s Solution in the usual manner. If it contain a large quantity of sugar, it must be diluted two or three times. In estimating with Fehling’s Solution it is well to attach a rubber tube 8 to 12 inches in length to the lower end of the burette, so that the boiling need not be done directly under the burette, and thus cause in- correct readings through the expansion of the liquid therein. 262 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XXIV. ESTIMATION OF GLYCERIN. Glycerin (Glycerol) C.H.(OH), = | -The estimation of glycerin, of fats, etc., may be made by the method of Benedikt and Zsigmondy. This method consists in saponifying the fat and oxidizing the result- ant glycerin by permanganate in alkaline solution ; thus oxalic acid, carbon dioxide, and water are formed The excess of permanganate is then destroyed by sulphurous acid or a sulphite, the liquid filtered to separate the manganese dioxide, and the oxalic acid then precipi- tated by a soluble calcium salt in the presence of acetic acid, and the precipitated calcium oxalate then titrated with permanganate, or after ignition and conversion into carbonate titrated with standard acid solution in the usual way. Aqueous solutions of glycerin may of course be sub- mitted to the method very easily. The reactions are as follows: C 3HS(OH)3 + 2KMn04 = K2C204 g2 (Potassium oxalate) 166 + KtCO, + 4MnOl + 4H10; then K.C.A + CaCl2 = 2KG + CaC204; 166 (Calcium oxalate) 12S A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 263 then 5CaC204 + 8H2S04 + 2KMn04 = SCaSO4 100)640 100)315 N 6.40 gms. 3.15 gms. or 1000 cc. V. S. 10 + 2MnS04 + K3S04 + 8H20 +iioCs N thus 1000 cc. permanganate solution represents 6.4 gms. of calcium oxalate, which is equivalent to 8.3 gms. of potassium oxalate, which is equivalent to 4.6 gms. of glycerin. Thus each cc. of the permanganate solution of deci- normal strength used up by the calcium oxalate repre- sents .0046 gm. of glycerin. If the precipitated . calcium oxalate is ignited and converted into carbonate, and the carbonate then titrated with decinormal sulphuric or hydrochloric acid, the reactions are as follows: 2CaC204 0, = 2CaC03 + 2C02; 4)256 4)200 10) 64 10) 50 _ 6.4 gms. 5.0 gms. 2CaC03 + 2H2S04 = 2CaS04 + 2HaO -f 2COa. 4)200 4)196 10) 50 i0)~49 N 5.0 gms. 4.9 gms. or 1000 cc. V, S. 10 Thus each cc. of decinormal acid represents 0.005 gm. of CaC03, or 0.0064 gm. of calcium oxalate, or .0046 gm. of glycerin. If experimenting with pure glycerin, operate upon 10 cc. of a 2 ether, benzine, benzol, or amylic alcohol. The 'Derated alkaloid is thus dissolved or washed out of aqueous solution. The alkaloid may be again abstracted from this solu- tion by the addition of a dilute acid, which forms again a salt of the alkaloid. Ti the U. S. P. chloroform is exclusively used as a solvent for alkaloids. The extraction is directed to be performed in a glass Separator or separatory funnel, which consists of an elongated (globular, cylindrical, or conical) glass vessel, provided with a well-fitting stoPper and an outlet-tube containing a " ell-ground glass stop-cock. (See Fig. 30.) When the alkaloidal solution, suitably PrePared, is introduced into the separator, and the chloroform subsequently added, the tatter, owing to its higher specific gravity, " tal form the lower layer. If the two are violently shaken together there will often result an emulsion, which separate slowly, and often imperfectly. Fig- 3°- This is particularly liable to happen if the aqueous liquid containing the alkaloid, either in solution or SUsPension, is strongly alkaline, or has a high specific 294 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. gravity. To avoid this formation of an emulsion it is better to frequently invert the separator or to rotate it rapidly than to shake it violently. The emulsion may sometimes be destroyed by the addition of more of the solvent, and, if necessary, aided by the application of gentle heat, or by the introduc- tion of a small quantity of alcohol or hot water. On withdrawing the chloroform solution of an alka- loid from the separator, a small amount of the solution will generally be retained in the outlet-tube by capil- lary attraction. If this were lost the results of the assay would be seriously vitiated. To avoid this loss, several successive small portions of chloroform should be poured into the separator without agitation, and drawn off through the stop-cock to wash out the out- let-tube. Another source of loss is due to the pressure gener- ated in the separator by the rise of temperature caused when an alkaline and an acid liquid are shaken together. Some of the liquid adheres to the juncture of the stopper and neck, and when the stopper is loosened some of the liquid is ejected. When an alkaline carbonate is used instead of caus- tic alkali for liberating the alkaloid, the liquids should be cautiously and gradually mixed by rotation, and the separator left unstoppered until gas is no longer given off. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 295 CHAPTER XXIX. estimation of the alkaloidal strength c SCALE SALTS. E our gms, of the scales are dissolved in 30 cc. of Aater in a capsule with the aid of gentle heat. The solution is cooled and transferred to a glass separator ; an aqueous solution of 0.5 gm. of tartaric acid is then aclded, followed by an excess of solution of sodium ydroxide. The tartaric acid prevents the precipita- tion of Fe2(OH)6, and the NaOH sets free the alkaloid, le alkaloid is then extracted by shaking up the mix- tuie with successive portions of chloroform, 15 cc. each bine, The chloroformic layers are separated each tune and mixed, evaporated in a tared capsule on a 'Uater-bath, and the residue dried ioo° C. (212° F.), and weighed. Or the residue may be titrated by add- lng sufficient decinormal sulphuric or hydrochloric acid to dissolve the salts and still remain in excess, then titrating residually with decinormal NaOH or KOH to determine the excess of acid. GENERAL METHOD FOR THE ESTIMATION OF THE ALKALOIDAL STRENGTH OF EXTRACTS. One gm. of the extract is dissolved in 20 cc. of water, heating gently if necessary. 20 cc. of a solution con- taining 6 gms. of sodium carbonate are added, followed 296 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. by 20 cc. of chloroform. Agitate, warm gently, and separate the chloroform. Add to this 20 cc. of dilute sulphuric acid with an equal bulk of water, again agi- tate, warm, and separate the acid liquor from the chloroform. To this acid liquor add an excess of am- monia, and agitate with 20 cc. of chloroform. When the liquors have separated, transfer the chloroform to a weighed dish, and evaporate over a water-bath. Dry the residue for one hour at ioo° C. (2120 F.), and weigh. This process may be extended to almost any extract containing alkaloids, except opium. If the resi- due consists of only one alkaloid, the formula and molecular weight of which are known, it may be titrated instead of weighed. Assay of Extract of Nux Vomica.—Extract of nux vomica dried at ioo° C, 2 gms.; alcohol; ammo- nia-water sp, gr. 0.960, water, chloroform, decinormal sulphuric acid V, S., centinormal potassium hydroxide V. S., of each q. s. Put 2 gms. of the dried extract of nux vomica into a glass separator. Add to it 20 cc. of a previously prepared mixture of 2 volumes of alcohol, 1 volume of ammonia-water, and 1 volume of water. Shake the separator until the extract is dissolved. Then add 20 cc. of chloroform and agitate during five minutes. The chloroform dissolves the alkaloids which the ammonia liberated. Allow the chloroformic solution to separate, remove it as far as possible, pour a few cc. more of chloroform into the separator, and without shaking draw this off through the stop-cock to wash the outlet-tube. Repeat the extraction with two further portions of chloroform of 15 cc. each, washing the outlet-tube each time as just directed. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 297 Collect all the chloroformic solutions in a wide beaker; expose the latter to a gentle heat on a water- bath until the chloroform and ammonia are completely dissipated. Add to the residue 10 cc. of decinormal sulphuric acid measured accurately from a burette, stlr gently, and then add 20 cc. of hot water. When solution has taken place add 2 cc. of Brazil-wood T. S. (bhe sulphuric acid combines with the alkaloids, and forms sulphates of the alkaloids.) Now carefully run into this solution centinormal Potassium hydroxide V. S. until a permanent pinkish c°lor is produced, showing a slight excess of the alkali. Divide the number of cc. of centinormal po- tassium hydroxide used by 10. Subtract the number found from 10 fthe 10 cc. of acid first used), and 10 the number of cc. of the acid which went into com- bination with the alkaloids is found. The two principal alkaloids of nux vomica are strychnine and brucine, and it is assumed that they are Present in equal proportions; and thus the factor for total alkaloids is found by taking the mean of their re- spective molecular weights; Strychnine, 334 2)728 Brucine, 394 364 728 364 gms. of the total alkaloids of nux vomica will neutralize 1000 cc. of normal sulphuric acid. 36.4 gms. will neutralize 1000 cc. of decinormal sulphuric acid. Hence each cc. of decinormal sulphuric acid used in the above assay represents 0.0364 gm. of an equal mixture of strychnine and brucine. And by multi- 298 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. plying the number of cc. used by this factor, the quantity of these alkaloids in the 2 gms. of extract taken is obtained, and this quantity multiplied by 50 will give the percentage. The extract should contain 15 per cent of total alka- loids by the above assay. Fluid Extract of Nux Vomica is evaporated to a solid extract, and then assayed by the above pro- cess. Tincture of Nux Vomica is assayed by evaporating 100 cc. to dryness, and the residue then tested by the above process. It should contain 0.3 gm. of alkaloids. Assay of Extract of Opium.—Extract of opium dried at ioo° C.,4 gms.; ammonia-water, 2.2 cc. ; alco- hol, ether, water, of each a sufficient quantity. Dissolve the extract of opium in 30 cc. of water, filter the solution through a small filter, and wash the filter and residue with water until all soluble matters are extracted, collecting the washings separately. Evaporate in a tared porcelain capsule first the wash- ings to a small volume, then add the first filtrate, and evaporate the whole to a weight of 10 gms. Rotate the concentrated solution about in the capsule until the rings of extract are redissolved. Pour the liquid into a tared flask, and rinse the capsule with a few drops of water at a time until the entire solution weighs 15 gms. Then add 8.5 cc. of alcohol, shake well, add 20 cc. of ether, and shake again. Now add the ammonia-water, stopper the flask with a sound cork, shake it thoroughly during ten minutes, and set it aside in a moderately cool place for at least six hours, or overnight. A TEXT-BOOK OF VOLUMETRIC ANALYSIS; At the expiration of this time remove the stopper carefully, and brush into the flask any crystals which maY adhere to the cork. Place two rapidly acting, plainly folded filters, one within the other, in a small funnel, wet them well with ether, and decant upon the lnner one, the ethereal solution, as completely as pos- sible. Add io cc. of ether to the contents of the flask, r°tate, and again decant upon the filter; repeat this operation with another io cc. of ether. Then pour the liquid in the bottle upon the filter in small portions at a time, in such a way as to transfer the greater portion °f the crystals to the filter. When the liquid has passed through transfer the remaining crystals to the filter by nnsing the flask with several small portions of water, using not more than io cc. in all. Apply water to the crystals drop by drop, until they aie practically free from mother-liquor, and afterwards Wash them with a saturated alcoholic solution of mor- Plu'ne, added drop by drop. When this has all passed through displace the remaining alcohol by ether, using übout io cc. or more if necessary. Dry to a constant weight at a temperature not ex- ceeding 6o° C., and carefully transfer the crystals to a tared watch-glass and weigh them. The weight multi- plied by 25 gives the percentage of crystallized mor- pfiine present in the extract. Instead of drying and transferring the crystals to a watch-glass as above directed, the filter containing them may be immersed in some boiling water in a beaker, and an excess of decinormal sulphuric acid added to dissolve the crystals (the quantity being noted); a few drops of methyl orange are then added, 300 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. and the mixture titrated with decinormal potassium hydroxide. Deduct the quantity of the latter used from the quantity of decinormal acid first added, and the quantity of decinormal acid which combined with the morphine is found. 1000 cc. of normal acid represents one molecular weight of the alkaloid. 1000 cc. of decinormal acid represents one tenth of a molecular weight of the alkaloid (30.3 gms.); thus each N cc. of acid represents 0.0303 gm. of crystallized morphine. The number of cc. used, multiplied by this factor gives the quantity of morphine present in the 4 gms. of extract taken. This multiplied by 25 gives the per cent, of crystal- lized morphine; it should contain 18 per cent. Assay of Tincture of Opium (Laudanum).—Tinc- ture of opium, 100 cc. ; ammonia-water, 3.5 cc.; alco- hol, ether, water, each a sufficient quantity. Evaporate the tincture to about 20 cc., add 40 cc. of water, mix thoroughly, and set the liquid aside for an hour, stirring occasionally and disintegrating the resinous flakes ad- hering to the capsule ; then filter, and wash the filter and residue with water, collecting the washings sepa- rately. Evaporate first the washings to a small vol- ume, then add the first filtrate and evaporate to 14 gms. Pour the liquid into a tared flask ; rinse the cap- sule, and add the rinsings until the entire solution weighs 20 gms. Then add 12.2 cc. of alcohol; shake well; add 25 cc. of ether; shake again. Now add the ammonia-water, cork well, shake for ten minutes, and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. set aside for at least six hours or overnight, so that the crystals may form. At the expiration of this time decant the ethereal layer upon a double, plain, rapidly acting filter pre- viously wet with ether; add 10 cc. of ether to the con- tents of the flask, rotate, and again decant. Repeat this operation with another 10 cc. of ether. Then pour the liquid in the bottle upon the filter, in small portions at a time, so as to transfer the greater portion of the crystals to the filter, and wash the remaining crystals on to the filter with the aid of a small quantity of water, using not more than io cc. Then wash the crystals, first with a few drops of water, then with an alcoholic solution of morphine, and finally with ether to displace the alcohol. Dry the crystals to a con- stant weight and weigh on a tared watch-glass. If 100 gms. of tincture have been operated upon, the weight of the crystals is at once the per-cent, of crys- tallized morphine. The yield should be 1.3 to 1.5 gms. of morphine from 100 cc. of tincture. Assay of Opium.—Opium, in any condition to be valued, 10 gms.; ammonia-water, 3.5 cc.; alcohol, ether, water, each a sufficient quantity. Introduce the opium (which, if fresh, should be in very small pieces, and if dry, in very fine powder) into a bottle having a ca- pacity of 300 cc.; add 100 cc. of water; cork well. Agitate the bottle frequently during twelve hours ; then pour the whole as evenly as possible upon a wetted filter having a diameter of 12 cm., and when the liquid has drained off wash the residue with water carefully dropped upon the edges of the filter and contents until 15° cc. of filtrate are obtained. Then carefully trans- fer the moist opium back to the bottle by means of a 302 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. spatula, add 50 cc. of water, agitate thoroughly and repeatedly during fifteen minutes, and return the whole to the filter. When the liquid has drained off, wash the residue as before until the second filtrate measures 150 cc., and finally collect about 20 cc. more of a third filtrate. Evaporate in a tared capsule, first the second filtrate to a small volume, then add the first filtrate, rinsing the vessel with the third filtrate, and continue the evaporation until the residue weighs 14 gms. From this point proceed exactly as in the assay of tincture of opium. The weight of the crystals obtained, when multiplied by 10, represents the percentage of crystallized mor- phine present in the sample of gum. Opium should contain 9s; the powdered not less than 13$ nor more than 15$. Assay of Cinchona, U. S. P.—{a) For Total Alka- loids.—Cinchona, in No. 80 (or finer) powder and com- pletely dried at ioo° C., 20 gms.; alcohol, ammonia- water, chloroform, ether, normal sulphuric acid V. S., potassium hydroxide V. S., each a sufficient quantity. 20 gms. of the cinchona in very fine powder is intro- duced into a bottle provided with an accurately fitting glass stopper, and to this is added 200 cc. of a pre- viously prepared mixture of 19 volumes of alcohol, 5 volumes of chloroform, and 1 volume of ammonia- water ; the bottle is stoppered, and thoroughly and frequently shaken during four hours. The liquid is then passed through a plug of cotton in a funnel into another bottle, being careful that there occurs no loss by evaporation. 100 cc. of the clear filtrate (representing 10 gms. of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. to dryness. The crude alkaloids thus obtained are dissolved in 10 cc. of water and 4 cc. of normal sul- phuric acid with the aid of gentle heat. The cooled -solution is then filtered into a separator, and the beaker and filter washed with water until the washings- bo longer have an alkaline reaction, using as little water as possible. cinchona) are transferred to a beaker and evaporated Now add 5 cc. of potassium hydroxide V. S., or suf- ficient to render the liquid alkaline. The alkaloids are thereby reliberated, and may be shaken out by chloro- form. 20 cc. of chloroform are first added, and the extraction repeated, using 10 cc. at a time, until a drop °f the last chloroform extraction leaves no residue when evaporated on a watch-glass. The chloroformic extracts are then mixed, evapo- rated in a tared beaker, the residue dried at ioo° C. (212° F.), and weighed. The weight multiplied by 10 will give the percentage °f total alkaloids in the specimen tested. The volumetric method cannot very well be em- ployed here, as the alkaloids exist in varying propor- tions and are very numerous, thus making it difficult to find a factor which will answer for all cases. [b) For Quinine.—Transfer 50 cc. of the clear filtrate remaining over from the preceding process (and repre- senting 5 gms. of cinchona) to a beaker, evaporate it to dryness, and proceed as directed in the assay for total alkaloids, using, however, only half the amounts of volumetric acid and alkali there directed. Add the united chloroformic extracts containing the alkaloids in solution, gradually and in small portions at a time, to about 5 gms. of powdered glass contained in 304 A Text-book of volumetric analysis; a porcelain capsule placed over a water-bath, so that when the contents of the capsule are dry all or nearly all of the dry alkaloids shall be in intimate admixture with the powdered glass, and the chloroform com- pletely expelled. Now moisten the residue with ether, and having placed a funnel containing a filter (7 cm. in diameter) and well wetted wnth ether over a small graduated tube (A), transfer to the filter the ether- moistened residue from the capsule. Rinse the latter, several times if necessary, with fresh ether, so as to transfer the whole of the residue to the filter ; then percolate with ether, drop by drop, until exactly 10 cc, of percolate are obtained. Then collect another 10 cc. by similar slow percolation with ether in a second graduated tube (B). Transfer the contents of the tubes to two small tared capsules, properly marked (A and B), and evaporate to a constant weight at ioo° C. (212° F.) and weigh them. (The residue in (A) will con- tain practically all of the quinine, together with a por- tion of the alkaloid less soluble in ether; the residue in (B) will consist almost entirely of these alkaloids.) From the amount of residue obtained in (A) deduct that contained in (B). This will give approximately the amount of quinine present in the 5 gms. of sample. Multiply this by 20 and the percentage of quinine containing one molecule of water is obtained. Cinchona calisaya should contain not less than 5 per cent, of total alkaloids, and at least 2.5 per cent, of quinine. Cinchona succirubra should contain not less than 5 per cent, of its peculiar alkaloids. fluid extract are diluted with 8 gms, of water in an Assay of Fluid Extract of Ipecac.—B gms. of the A TEXT-HOOK OF VOLUMETRIC ANALYSIS. 305 ordinary vial, 32 gms. of chloroform and 48 gms. of other are added and shaken up; 4 gms. of ammonia Water are now introduced, and the mixture frequently agitated during half an hour. Fifty gms. of the chloroform-ether solution (repre- senting 5 gms. of the fluid extract) are separated, Poured into a tared flask, and the solvent distilled or evaporated off; the varnish-like residue is twice treated With 5 to 10 cc. of ether, and evaporated by forcing a current of air into the flask by means of a rubber bulb ; the residue is then dried in a water-bath and weighed. For the titration, the residue may be dissolved in a known quantity of decinormal hydrochloric acid ; the solution may be assisted by a gentle heat, or the addi- tion of a small quantity of alcohol; 10 or 12 drops of Fiazil-wood T. S. are then added and the excess of ucid determined by means of decinormal alkali, the latter being added until the liquid becomes cardinal to Purplish red in color. The quantity of decinormal alkali used is then sub- tracted from the quantity of decinormal acid first added. This gives the quantity of the decinormal acid which was used to neutralize the alkaloids present. Emetine, according to Kunz, is diacid, and has the formula C3OH 40N206, molecular weight 508. Therefore °ue molecule of emetine will neutralize two molecules °f hydrochloric, or, half a molecular weight. 254 in gmrnmes, will neutralize I litre of normal hydrochloric, acid, while 25.4 gms. will neutralize 1000 of decinormal acid. Thus each cc. of decinormal acid represents 0.0254 gm, of emetine. If acid is used, each cc. represents 20 0,0127 gm. of emetine. 306 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. C„H„N.O. + 2HCI = C„H„N.O.(HCI)I. Emetine (Kunz). 2)508 2)72.79 10)254 gms. 10)36.37 gms. or 1000 cc. _y g —' x 2) 25.4 gms. 2) 3.637 gms. or 1000 cc. JS.V. S. lO 12.7 gms. 1.818 gms. or xooo cc. V. S. 20 Thus if decinormal acid is, employed, the number of cc. which were neutralized by the alkaloid when mul- tiplied by ,0254 gm. gives the quantity of emetine present in 5 gms. of the fluid extract; and when this is multiplied by 20 the percentage is obtained. Assay of Ipecac Root.—lo gms. of the finely powdered and dried root are placed in a bottle having a capacity of about 150 cc.; 40 gms. of chloroform and 60 gms. of ether are added, and shaken well for several minutes; 10 gms. of ammonia-water are now added ; this liberates the emetine, which immediately dissolves in the chloroform and ether, while the suspended powder settles to the bottom of the bottle. The bottle is frequently shaken during one hour, and 5 gms. more of ammonia-water added ; the powder then agglu- tinates in a lump, and the liquid becomes perfectly clear. 50 gms. of the chloroform-ether solution are now taken (representing 5 gms. of the root) and transferred to a tared flask, and the process completed as described under the assay of the fluid extract. The titration is in this case a little more difficult be- cause of the presence of fat from the root. It is advis- able to extract the fat from the root before subjecting it to this assay. Estimation of the Strength of Resinous Drugs. —Take 5 to 10 gms. of the drug in powder, and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 307 place it vn a strong glass flask with 100 cc. of pure alcohol (U. S. P. and free from resin). Close the flask 'With a good cork, and digest it in a warm place at about 49 C. (120° F.) for 12 hours, shaking from time to tune. Pour or filter off 80 cc. (representing T of the total drug taken), place it in a weighed beaker, and ovaporate to 25 cc. on the top of the water-bath. Now add 50 cc. of distilled water, and boil gently over a low gas flame till all the alcohol is driven off. Let it cool and perfectly settle, pour off the supernatant liquor, wash the deposited resin by decantation with hot dis- tilled water, and then dry the beaker and its contents |n the air-bath at 105° C. (220° F.) and weigh, deduct- lng the tare of the beaker. Thus treated, jalap, for oxample, should show 12 per cent of resin, of which not over 10 per cent should be soluble in ether, Scam- m°ny should show 75 per cent resin, which is entirely soluble in ether and in solution of potassa. From the latter it is not reprecipitated by dilute hydrochloric acid in excess. For other resinous drugs no official standard has yet been laid down. 308 a text-book of voi I]metric analysis. CHAPTER XXX. GLUCOSIDES. GIUCOSIDES are proximate vegetable principles, which when boiled with a dilute acjd, or subjected to some other method of decomposition, take up the ele- ments of water, and yield glucose and some other sub- stance, this other substance differing in each case according to the particular glucoside operated upon. Upon this property of these bodies is based a method for their estimation. This method depends upon converting the glucoside into glucose, and then estimating the glucose by Feh- ling’s solution in the usual way, and from the amount of glucose formed calculating the quantity of the gluco- side. The conversion of glucosides into glucose is shown by the following equations : Cl 3H1807 + H,O = C 6H4(OH)CH2 + C 6H1206. Salicin, 286. Saligenol. Glucose, 180. Thus it is seen that 180 gms. of glucose are derived from 286 gms. of salicin. C 37 -f~ 2HaO Cl 5H2606 + 2C6HiaO, Digitalin. Digitaliretin. Glucose. C3lH50Oie + SHaO = Cl 3H2403 + 3C6H120#. Jalapin. Jalapinol. Glucose. CMH160. + HaO = C) 8H2604 + c 6h130, Glycyrrhizin. Glycyrrhetin. Glucose. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XXXI. MILK. Milk is the nutritive secretion of glands (the mam- niary glands) which are characteristic of the mam- malia. Ihis secretion takes place as a result of pregnancy and delivery, and continues for a variable period, con- stituting the entire food of the young animal until it ls able to live upon other foods. The milk of different animals contains qualitatively Mentical or analogous ingredients to that of the cow, namely, fat (which is held in suspension), nitrogenous matters such as casein and albumen, milk sugar, in- organic salts, and water. The average composition of cow’s milk is as follows : Fat 3.65 per cent. Froteids . 440 “ U Lactose 4-25 “ u Inorganic salts 0.75 “ u Total solids 13-OS “ (( Water u 100.00 In the milk of different animals, however, these in- giedients are in different proportions, as the following fable shows; A TEXT-BOOK OF VOLUMETRIC ANALYSIS Human. Goat. Mare. Ass. per cent. per cent. per cent. per cent. Fat 3-40 5-2 I. I 1.0 Proteids 2-45 3-8 2.2 2-7 Lactose 5-75 4-3 5-8 5-3 Inorganic salts 0-35 0.7 0-3 0.4 Water 88.05 86.0 90.6 90.6 100.00 100.0 100.0 100.0 Total solids 11.95 14.0 9 4 9.4 Milk is a perfect natural emulsion. The casein appears to be the emulsifying agent, a film of which envelops each globule of fat, thus preventing cohesion. The inorganic salts are chiefly the phosphates of sodium and calcium, and the chlorides of sodium and potassium, but magnesium and iron are also generally present. The proteids consist mainly of casein with some al- bumen, the proportion being about as 6 to I. Besides the above-mentioned constituents milk also contains a very small quantity of peptone, kreatin, leucin, etc. Also gases, such as C02, O, and N. Colostrum is the milk secreted in the early stages of lactation ; it is rich in proteids, often containing as much as 20 per cent, and contains a few corpuscles of a peculiar character, which look like epithelium-cells, called colostrum corpiiscles. Reaction.—The reaction of the milk of herbivorous animals is generally alkaline, that of carnivora is gener- ally acid. The reaction of cow’s milk is generally neutral, sometimes slightly acid, rarely alkaline. Specific Gravity.—This varies in normal cow’s milk from 1.029 to 1.035. should not be below 1.029. a Text-Book of Volumetric analysis. 311 An excess of fat lowers the specific gravity and the temoval of fat raises it. Thus skimmed milk has a higher specific gravity than normal milk. These facts are made use of for the detection of the ordinary adulterations. Determinations of the specific gravity of milk should always be made at the temperature of 6o° F., and may be made by any of the ordinary methods.* See table of corrections for temperatures other than 6o° F., page 312. A special hydrometer known as the lactometer is, however, generally used. The lactometer is graded Dorn o° at the top to 120° at the bottom. In taking the specific gravity with this instrument the tempera- ture of the milk must be 6o° F. For every 2%° of temperature above the 6o° standard, one degree is to be added to the reading of the lactom- oter; below 6o° F. a similar subtraction is to be made. On the lactometer scale o° = 1.000, the specific gravity of pure water; at 6o° F. 100 = 1,029, the specific gravity of the poorest possible milk at the same temperature. If in a sample of milk the lactometer stands at Bo° the sample contains about 80 per cent of standard milk and 10 per cent of water. If the lactometer stands at 9°°, the sample contains about 10 per cent of water. Lactometer Reading'. Specific Gravity. Lactometer Reading. Specific Gravity. O 1.0000 70 I.0203 IO 1.0029 80 I.0232 20 1.0058 90 1.0261 30 1.0087 100 I.O29O 40 1.0116 no I.0319 50 I.0145 120 I.0348 6o 1.0174 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Table for Correcting the Specific Gravity of Milk according to Temperature. {From Muter s Analytical Chemistry.') Directions for Use.—Find the temperature of the milk in the uppermost horizontal line, and the observed specific gravity in the first and last vertical lines. In the same line with the latter, under the temperature is given the corrected specific gravity Example.—Supposing the temperature to be 59° and the observed specific gravity 1.032.0, at 6o° the specific gravity will be 1.031.9. A specific gravity of 1.032.0 at 66° will be 1.032.9 at 60°. Observed Specific Gravity. Degrees of Thermometer (Fahr.). 50° 51° 52° 53° 54° 55° 56° 57° 58° 59° 60° 61° 62° 63° 64° 65° 66° 67° 68° 69° 70° 1.020.0 19.3 *9-3 19.4 19.4 19-5 ig.6 19.7 ig.8 ig.919.9 1.020.0 20. T 20.2 20.2 20-3 20 4 20.5 20.6 20.7 20.9 21 .O 1.021.0 20.2 20.3 20.3 20.4 20.5 20.6 20.7 20.8 20.9 20.9 1.021.0 21.1 21.2 21.3 21.4 21 ■ 5 21.6 21.7 21.8 22.0 22 . I 1.022.0 21.2 21.3 21.3 21.4 21-5 21.6 21.7 21.8 21.9 21.9 1.022.0 22.1 22.2 22 3 22.4 22.5 22.6 22.7 22.8 23.O 23 . I 1.023.0 22.2 22.3 22.3 22.4 22.5 22.6 22.7 22.8 22.8 22.9 1.023.0 23.I 23.2 23-3 23-4 23-5 23.6 23-7 23.8 24.O 24.I 1.024.0 23.2 23-3 23-3 23-4 23-5 23.6 23.6 23-7 23.8 23-9 1.024.0 24.1 24.2 24 • 3 24 ■ 4 24-5 24.6 24.7 24.9 25.O 2S.i 1.025.0 24.I 24.2 24-3 24.4 24-5 24.6 24.6 24.7 24.8 24.9 1.025.0 25.1 25.2 2 5 ■ 3 2S»4 25-5 25 6 25-7 25-9 26.O 26.1 1.026.0 25.I 25.2 25.2 25-3 25 -4 2S-5 25.6 25.7 25.8 2S- 9 1.026.0 26.1 26.2 26.3 26.5 26.6 26.7 26.8 27.0 27.1 27.2 1.027.0 26.I 26.2 26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 1.027.0 27.1 27- 3 27.4 27-5 27.6 27.7 27.8 28.0 28.1 28.2 1.028.0 27.O 27. I 27.2 27-3 27.4 27.5 27.6 27.7 27.8 27.9 1.028.0 28. I 28.3 28.4 28.5 28.6 28.7j28,8 29.0 29 . I 29.2 1.029.0 28.0 28.1 28.2 28.3 28.4 28.5 28.6 28.7 28.8 28.9 1.029.0 29.I 29 ■ 3 29.4 29-5 29.6 29.8 29.9 3°-1 3°.2 3°-3 1.030.0 29.O 2Q.I 29.I 29.2 29-3 29.4 29.6 29.7 29.8 29-9 1.030.0 3°. 1 3° 3 3° - 4 3°-S 3°-7 30.8 30.9 31 •1 31.2 3i-3 1.031.0 29.9 30.0 30.1 3°.2 3°- 3 3°-4 3°'5 30.6 30.8 3°-9 1.031.0 31'2 3*-3 3i-4 31 ■ 5 31 • 7 31-8 32.0 32-2 32.2 32-4 1.032.0 3°-9 31 .O 31-r 31.2 3i-3 31 ■ 4 3T • 5 31.6 31 ■ 7 31-9 1.032.0 32.2 32 • 3 32-5 32 -6 32-7 32-9 33-o 33-2 1 33-3 33-4 1.033.0 31.8 3l-9 32-° 32 ■1 32 • 3 32-4 32-5 32.6 32-7 32-9 1.033.0 33-2 33-3 33-5 33-6 33-8 33-9 34-qI34-2 1 34-3 34-5 1.034.0 32 7 32-9 33-0 33-1 33 2 33-3 33-5 33,6 33-7 33-9 1.034.0 34-2 34-3 34'5 34-6 34-8 34-9 35-o 35-2 1 35-3 35-5 1.035.0 33 6 33-8 33-9 34 -o 34-2 34-3 34-5 34-6 34-7 34-9 1.035.0 35-2 35 3 35-5 35-6 35.8 35-9 36.1 36.2 36-436.5 1 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 313 The Adulterations of Milk .—The adulterations usually practised are the abstraction of cream (skim- ruing) or the addition of water, or both. Occasion- ally the addition of some foreign substance, as sodium carbonate, borax, common salt, or sugar, is met with ; °r preservatives, as boric or salicylic acids. The detection of adulterations usually depends upon the determination of the specific gravity, the fat, total solids, and the ash. These ingredients are, however, present in milk in varying proportions, and hence certain limits of allow- able variations have been determined upon from time to time. The standard adopted in many States in this country ls> for specific gravity, not less than 1.029, for total sol- Jds, not less than 12 per cent., for fat 3 per cent. The total solids may vary legally from 12 to 13.13 per cent., and the solids not fat, from 8.5 to 9.5 per cent. Estimation of Total Solids and Water.—A small, shallow platinum or porcelain dish about mches in diameter is heated to redness, allowed to cool, and weighed. About 5 cc. of milk are then put in, and again weighed. The difference between the two Weighings gives the weight of the milk taken. Now place the dish on a water-bath and heat until the milk ceases to lose weight. Then cool again and weigh. The weight of the dry residue minus the tare of the dish equals the total solids. Then by multiplying this by 100, and dividing by the weight of milk taken, the percentage of total solids 15 found. Thus, total_solids X 100 = per.cent. of total solids, w&ight of milk 314 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. This deducted from 100 gives the per-cent, of water. Fat.—Where great accuracy is unnecessary the fat may be determined by treating the total solid residue with successive portions of warm ether until the fat is completely dissolved out. The ethereal solution is then evaporated and the fat which remains behind is weighed, or the residue in the dish may be again weighed. The loss of weight then represents the fat. The results so obtained are 0.3 to 0.5% too low. Adams Method is the officially recognized method for the accurate estimation of fat in milk. This consists essentially in spreading the milk over absorbent paper, drying, and extracting the fat. The paper used for this purpose must previously have been thoroughly exhausted with alcohol and ether, and should be in long narrow strips. The procedure is as follows: 5 cc. of the milk are put into a small beaker and weighed. A strip of the absorbent paper which has been rolled into a coil is thrust into the beaker containing the milk. In a few minutes nearly the whole of the milk will be absorbed ; the coil is then withdrawn, and stood dry end down upon a sheet of glass. It is important to take up the whole of the milk from the beaker, as the paper has a selective action, removing the watery constituents by preference over the fat. The beaker is again weighed, and the milk taken found by difference. The paper charged with the milk is now dried in a water-oven and placed in a Soxhlet extraction apparatus (Fig. 28). About 75 cc. of ether are introduced into the tared flask of the apparatus, and heat applied by means of a A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 315 Water-bath and continued until exhaustion is com- plete. The flask is then detached, the ether removed by distillation, and the fat which remains is weighed. 1 he paper may be charged with the milk by spread- lng the latter over the surface of the paper by means °f a pipette. The Werner-Schmid Method.— This is a satisfactory and at the same time a rapid method for the determin- ation of fat, and is especially suitable for sour milk. io cc. of the milk are put into a long tube having a capacity of about 50 cc., and 10 cc. of strong hydrochloric acid are added; or the milk may be weighed in a small beaker and washed into the tube with the acid. The liquids are mixed and boiled for if minutes, or until the liquid turns dark brown, but not black. The tube and contents are then cooled, and 30 cc. of ether are added, shaken, and allowed to stand until the acid liquid and ether have separated. The cork is now taken out and the wash-bottle arrangement inserted (see Fig. 27). The stopper of this should be of cork, not of rubber, since the ether has a solvent action upon the latter. The lower end of the exit tube is adjusted so as to rest immediately above the junction of the two liquids. The ethereal solution of fat is then blown off, and received in a weighed beaker. Two more portions of 10 cc. each are shaken successively with the acid liquid, blown out, and added to the first. The ethereal solution is then heated on a water-bath, and the residue of fat weighed. The results agree quite closely with the Adams method. Calculation Method.—This rests upon the assumption that every per-cent, of solids not fat, raises the specific gravity by a definite amount, while every per-cent, of 316 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. fat lowers it by a definite amount. An accurate de- termination of the per-cent of total solids and of the specific gravity therefore furnish the necessary data for calculating the amount of fat. Hehner and Richmond have devised the following formula: F 0.859 T 0.21866-.; in which F fat, T = total solids, and G the last two units of the specific gravity and any decimal. Thus if the specific gravity is 1029, Cwill be 29; if 1029.5, G will be 29.5. Example.—Let us assume in the examination of a certain milk that the specific gravity was 1030, and that it contained 12 per cent, of total solids. We then have Fat = 0.859 X 12 0.2186 X 30 = 375$ When the per-cent, of fat is known, the formula may be transposed so as to calculate the total solids, as follows : j, _ F + 0.2186(9 0.859 Example.—A sample of milk is found to contain 3.75 per cent, of fat, and its specific gravity is 1030; then . ... 3.75+0.2186x30 . Total solids = 12io 0.859 Ash.—The ash may be determined by igniting at a dull-red heat the residue left after the fat has been extracted from the total solids. The organic matter is thus all burned off, and the residue is weighed and cal- culated as ash. The ash should be about 0.75 per cent, never below 0,67. To Calculate the Per cent, of Pure Milk and of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 317 Added Water, the following formula maybe adopted, which is based upon the legal standard of the State of New York, which is based upon the poorest possible natural milk, viz., 3 per cent, of fat, 12 per cent, of total solids, and 9 per cent, of “ solids not fat.” If, however, a milk has 3 per cent, of fat and only 8.5 Per cent, of “ solids not fat,” it need not be considered as definitely proved to be adulterated. The quantity of added water should, however, always be calculated upon the average standard of 9 per cent ‘solids not fat,” provided the milk is certainly well below the limit of 8.5 per cent. The “solids not fat” are used as a basis for the cal- culation because they are a fairly constant quantity, tbe fat being variable. The calculation is made thus : “ Solids not fat” X 100 , — = p. c. of pure milk present; aud the difference between this result and 100 will of course give the added water. Example. A sample of milk upon analysis was lound to contain 8.1 per cent of solids not fat; then B.i X ioo 810.0 , = -■ = 9 OJo 9 9 °f pure standard milk and 10 per cent of water. Total Proteids.—Rittenhauseris Copper Process.— The solutions required are: (1) Copper-sulphate solu- tion, 34.64 gms. in 500 cc.; (2) Sodium-hydroxide solu- tion, 12 gms. to 500 cc. 10 gms. of the milk are diluted to 100 cc. with dis- tilled water and placed in a beaker; 5 cc- °t the cop- per-sulphate solution are now added and thoroughly mixed. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. The sodium-hydroxide solution is now added drop by drop, stirring constantly until the precipitate settles quickly, and the liquid is neutral or feebly acid. It should never be alkaline, as an excess of alkali pre- vents the precipitation of some of the proteids. The precipitate which includes the fat carries down all of the copper. It is washed by decantation and collected upon a weighed dry filter, the contents of the filter being washed until the total filtrate measures about 250 cc. This filtrate, which contains no copper, is reserved for the determination of the sugar by Feh- ling’s Solution. The precipitate is washed once by strong alcohol to remove adhering water; it is then washed several times with ether to remove the fat. The residue on the filter, which consists of the proteids and copper hy- droxide, is dried at 265° F. in the air-bath and weighed. It is then transferred to a porcelain crucible and incin- erated, and the residue weighed. The weight of the filter and contents less the weight of the filter and residue after ignition, gives the weight of the proteids. The Milk-sugar is estimated in the mixed filtrate from the precipitated proteids by the use of Fehling’s Solution in the usual way. (See Estimation of Sugar.) A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 319 CHAPTER XXXII. BUTTER. The composition of commercial butter usually varies within the following limits : Fat 78-94$ Curd i-3 Water 5-14 Salt o-7 (Leffmann and Beam.) Reichert’s Process for the detection of foreign fat ln butter is undoubtedly the best. This process is based upon the presence in butter- fat of tributyrin, which yields when appropriately treated an acid (butyric acid), which is relatively much more volatile than the other acids yielded by any of the fats which may be used for the adulteration of butter. The process is as follows : 2.5 gms. of the butter are melted and filtered into a flask having a capacity of about 150 cc., 20 cc. of a 5-per-cent alcoholic solution °f potassium hydrate are added, and the mixture heat- ed to gentle ebullition on a water-bath until the fat is entirely saponified and the alcohol expelled. The soap, which should form an almost dry mass, not readily detachable from the bottom of the flask by shaking, is dissolved in 50 cc. of water by the aid of 320 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. gentle heat. When solution is effected, 20 cc. of dilute sulphuric acid are added. This decomposes the soap and liberates the fat acids. The flask is then connected with a Liebig’s condenser and the contents heated to moderate boiling, a few small pieces of glass, broken clay pipe, or pumice-stone being introduced to prevent bumping. The distillate, which contains some insoluble acids, is passed through a small wet filter as it drops from the condenser, and is received in a 50-cc. measure. The distillation is continued until exactly 50 cc. has come over. This distillate contains the volatile and soluble fat acids of the butter examined, and is at once titrated with decinormal sodium-hydroxide solution, using phenolphthalein as an indicator. When thus treated, pure butter seldom yields less acidity than is represented by 12 cc. of decinormal soda. When butter is made from the milk of a single cow it sometimes falls to 11.5 cc. Reichert’s formula for determining the percentage of butter-fat in mixed fat is B = 7-3(» - o-3), N n being the number of cc. of alkali used in neutral- -10 izing the distillate from 2.5 gms. of the fat. Oleomargarine requires only 0.8 to 0.9 cc. of alkali for the neutralization of the distillate from 2.5 gms; cacao butter requires 3.7 cc. ; lard, 0.6 cc. A rapid method for detecting oleomargarine or an admixture of it with butter is to heat the suspected substance in a small tin dish directly over a gas flame. If it melts quietly, foams, and runs over the dish, it is A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 321 butter; if it sputters noisily as soon as heated and foams but little, it is oleomargarine. Another way is to heat the butter for a moment with an alcoholic solution of sodium hydroxide and then empty into cold water. It gives a distinct odor °f pineapples (due to ethyl butyrate), while oleoman garine gives only an alcoholic odor. 322 A TEXT-BOOK OE VOLUMETRIC ANALYSIS, CHAPTER XXXIII. URINE. Normal Urine when fresh is clear and transparent. Its color is yellowish, reddish, or colorless. It has a peculiar odor, a distinctly acid reaction, and its average specific gravity is from 1018 to 1022. On standing it generally gives a slight cloud of mucus, which slowly sinks to the bottom ; and after heavy exercise or a hearty meal of nitrogenous food, a sediment of urates. If the urine be very dilute and the temperature is above the mean, decomposition rapidly takes place., and the urine becomes turbid, acquires an alkaline re- action, and develops a nauseous ammoniacal odor. Reaction.—The acid reaction of fresh urine is proba- bly due to the presence of acid phosphate of sodium. If it has an alkaline reaction when first voided it is probably due to the conversion of urea into ammo- nium carbonate within the bladder ; it is then generally turbid, and indicates an abnormal condition. The reaction is best tested by dropping a small piece of a red and a blue litmus-paper into it. If both are found red in a few minutes the reaction is acid, if both are blue it is alkaline, if both remain unchanged it is neutral. Composition.—The average composition of healthy urine is as follows: A TEXT-BOOK OF VOLUMETRIC ANALYSIS 323 Per Cent Grains per diem Water.,. Solids as tabulated below 4.00 icoo grs. Urea Uric acid.. . . Hippuric acid Creatinine.. . 15.0 “ Pigment, mucus, xanthine, and othei extractives Chlorides of potassium and sodium.... -ulphates of potassium and calcium.. . Phosphates of potassium and sodium, f hosphates of magnesium and calcium. 0.50 0.11 0.12 0. So 170.0 “ 40.0 “ 45.0 “ 35-5 “ Beside these there have been found traces of indican, diastase, glucose, oxalic acid, lactic acid, carbolic acid, and unoxidized sulphur and phosphorus, (From “ The Urine ; ” Holland.) The composition of urine is not constant: it is influ- enced by the amount of water and other fluids taken, by the temperature of the skin, by the emotions, the blood-pressure, the amount of work done, the time of day, age, sex, and medicine. The Quantity passed in 24 hours varies considerably. The average quantity passed daily by a healthy adult 15 I4°o to 1600 cc.—about 50 fl. ozs. The quantity of total solids contained in this is, as seen in the table, about 60 gms., or 1000 grains. About one half of these S°lids is composed of urea. In making an analysis of urine the analyst looks for the presence of abnormal constituents, and determines the excess or deficiency of the normal constituents ; and therefore, since the composition of urine is not the same at all hours of the day, it is important when accurate tesults are desired to examine a portion of the total Quantity of the urine passed in twenty-four hours. If 324 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. this cannot easily be obtained, or only a casual ex- amination is to be made, the first urine passed in the morning may be used. Specific Gravity.—This varies from 1015 to 1028, according to the degree of dilution or concentration. But pathological urine may vary from almost that of water to 1050. The urine of Bright’s disease is, as a rule, of low specific gravity, and in diabetes of high specific gravity. The specific gravity may be taken by any of the usual methods, but the urinometer (a special hydrom- Fig. 31. eter; see Fig. 31) is generally used for this purpose. This instrument is usually graduated so that only the last two figures of the specific gravity appear upon the stem, and so as to read correctly at 6o° F. If the tem- perature is above 6o° F. it will be sufficiently accurate for ordinary clinical purposes to add one degree in specific gravity for every 10 degrees of temperature ; that is, if it read 1018 at Bo° F., it would read 1020 at 6o° F., or for every i° F. above 6o° add 0.0001 to the observed specific gravity. The urinometer is used as follows: Sufficient urine is placed in the upright jar or cylinder to float the urinometer, which is carefully A TEXT-BOOK OF VOLUMETRIC ANALYSIS. introduced. When it has come to rest bring the eye °n a level with the surface of the liquid in the jar, and take the reading at the lower edge of the meniscus foirned by the upper surface of the urine. The mark on the instrument which is cut by this iine, and which can be distinctly seen, is taken as t*he correct reading. 325 If the urine be turbid this method cannot be em- ployed. After taking the specific gravity, reaction, etc., set a portion of the urine aside in a conical glass so as to allow a deposit to form, which must be examined microscopically and chemically, as described later on. Total Solids .—The total solids in urine may be 1 ouglily estimated as follows: The last two figures of the specific gravity when multiplied by the factor 2.33 will give the number of grammes of solid matter in 1000 cc. of the urine. hrom this it is easy to calculate the quantity of solids Passed in twenty-four hours. for example, 1500 cc. of urine were passed in twenty-four hours, and the specific gravity of this was 1020, the total solids would be 20 X 2.33 = 46.6 gms, in 1000 cc. In 1500 cc. there will be 4-6-6 Xl 5 _ sqq 10 gms. If it be desired to use the English measures, we may determine the total solids by multiplying the last two figures of the specific gravity by the number of fluid ounces of urine passed, for these last two figures represent approximately the grains of solid matter in a fluid ounce. Thus if 50 fluid ounces were passed and the specific gravity is 1020, the total solids will be 5° X2O = 1000 grs. in twenty-four hours. 326 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. A more exact method of determining the total solids is to evaporate 10 cc. in a white porcelain dish and dry in a water-oven to a constant weight. The difference between the weight of the dish, and of the dish with the solids will be the weight of the solids in 10 cc. of urine. Even by this method there is some loss through volatilization. Chlorides.—For the detection of chlorides a few drops of nitric acid are added to the urine in a test- tube, and then silver-nitrate test solution. A white, curdy precipitate of silver chloride forms, which should occupy not more than one fourth the volume of the urine taken. If it occupies more, the chlorides are said to be increased ; if it occupies less space than one fourth, the chlorides are diminished. It is always ad- visable to compare the specimen under examination with normal urine, subjected to the same test. In most cases such an approximate result is all that is re- quired in a clinical examination. The Volumetric Estimation.—lt is sometimes neces- sary to make a more accurate determination. For this purpose a decinormal solution of silver nitrate is used. 10 cc. of the urine are diluted with about 50 cc. of water; a few drops of potassium chromate T. S. are added, and then the decinormal silver nitrate V. S. run in from a burette until a permanent reddish color is pro- duced. Note the number of cc. of the V. S. used, and multiply this number by the factor for chlorine, 0.00354 gm.,the factor for sodium chloride, or 0.00584 gm. This will give the quantity of chlorine or sodium chloride in 10 cc. of urine. This when multiplied by 10 gives the per- centage. In highly colored urines this method is some- times inapplicable, because the change of color is A TEXT-BOOK OF VOLUMETRIC ANALYSIS. hidden by the color of the urine. In such cases Vol- hard’s method (see page 112) may be employed. Phosphates.—Phosphoric acid exists in the urine combined with the alkalies and with the alkaline earths. These phosphates are, therefore, generally distinguished by the terms alkaline and earthy phosphates. By adding an alkali to normal urine the earthy phosphates (calcium and magnesium) are precipitated. The earthy phosphates may be approximately estimated by adding a few drops of ammonia-water to the urine and observing the amount of turbidity pro- duced after boiling. By comparing this with the amount obtained by the same treatment of normal urine the excess or deficiency is determined. The ppt. is Ca,(PO4)2 and MgNH4P04. The alkaline phosphates may be detected in the filtrate from the earthy phosphates by the addition of a few drops of magnesium-sulphate solution and some ammonium chloride. The precipitate will be much more voluminous than that produced by the earthy phosphates, and the excess or deficiency may be determined by comparison with normal urine. The precipitate has the composition MgNH4P04. The quantitative estimation of the phosphate is rarely required, but may be made by the volumetric process with uranium nitrate. Sulphates.—About 30 grains or 2 grammes of sul- phates are daily discharged in the urine. Test.—A few drops of hydrochloric acid are added to the urine in a test-tube to prevent the formation of barium phosphate. Barium chloride T. S. is now added, which causes a white precipitate in the presence of sulphates. This should be compared with results 328 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. obtained from equal quantities of healthy urine treated in the same way. Volumetric Estimation.—This is done by the use of a standard solution of barium chloride. The Gravimetric Method.—Take 100 cc. of urine, add 5 cc. HCI and heat to near boiling, then add barium chloride T. S. in slight excess ; place the beaker con- taining the mixture on a water-bath until the pre- cipitate has subsided, decant the clear liquid carefully from the precipitate, add hot water, and when the pre- cipitate has again settled decant again ; continue this until the decanted liquid no longer gives a cloudiness with sulphuric acid. Then dry the precipitate and weigh carefully. This gives the quantity of BaS04 which is precipitated out of the urine by barium chloride. 207.7 parts of barium sulphate represent 98 parts of sulphuric acid. Therefore by multiplying the weight obtained by 98 and dividing by 207.7 the number of grammes of sulphuric acid in the 100 cc. of urine taken is obtained. From these we can easily calculate the quantity eliminated in twenty-four hours. Total Acidity.—Place 50 cc. of the urine in a beaker, add 3 or 4 drops of phenolphthalein, and then run into the beaker carefully from a burette decinormal sodium hydroxide V. S. until a faint permanent red color appears. The number of cc. of the decinormal alkali used multiplied by 0.0063 gives the acidity of 50 cc. of the urine, expressed in grammes of oxalic acid. PTom this the total acidity is determined by multiplying by the quantity of urine passed in twenty-four hours, and dividing by 50. If the urine is highly colored the end reaction is A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 329 sometimes difficult to see. In such a case the color may be removed by shaking up a portion of the urine with coarsely powdered animal charcoal, then filtering. The urine is thus decolorized, and the pink color pro duced by the indicator at the completion of the reaction is easily seen. Urea, CO(NHS)2.—This is the most important con- stituent of the urine, as it is the chief condition in which the nitrogen leaves the body. It may be detected by evaporating a few drops of urine on a glass slide, moistening with nitric acid, allowing it to crystallize, and examining the crystals of urea nitrate under a microscope of low power. As urea is generally looked upon as an index of the retrograde changes going on in the body, or of the eliminating power of the kidneys, its quantitative estimation is a matter of great import- ance. The quantity of urea eliminated in twenty-four hours has been put as being 30 to 33 gms., or from 430 to 550 grains. The Quantitive Estimation of Urea is effected by treating it with alkaline hypochlorites or hypobromites which decompose the urea into COa, N, and HaO. Uric Acid, C 6H4N403, occurs in urine, sometimes in a free state, but oftener in combination with potassium, sodium, or ammonium, and occasionally with calcium and magnesium. These are called urates. It is de- tected microscopically, and varies in quantity from 0.4 to 0.8 gm. (6 to 12 grs.) in twenty-four hours. The crystals are sometimes large enough to be seen by the naked eye. It deposits, upon standing, in the form of a brick-colored precipitate, commonly called brick- dust. 330 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Qualitative Chemical Tests.— The Murexid Test.—A portion of the urine is evaporated to dryness in a porcelain dish upon a water-bath. The residue is then moistened with nitric acid, and after evaporating off the nitric acid the residue is moistened with am- monium hydroxide. If uric acid is present the residue assumes a beautiful purple-red color, due to the forma- tion of murexid. The Silver-carbonate Test.—Make the urine alkaline with Na2COs or K2COs, and moisten a filter paper with the liquid. Now touch the moistened paper with a solution of AgNOs. In the presence of uric acid a distinct gray stain is produced. Quantitative Estimation of Uric Acid.—Acidulate a portion of the urine with HQ, and set aside for twenty- four hours. The uric acid is thus set free, and, being insoluble, precipitates and adheres to the bottom and sides of the vessel. It is collected on a weighed filter, washed thoroughly, dried, and weighed. The heat used should not be over ioo° C. (2120 F.). The weight of the filter and its contents minus the weight of the filter alone gives the weight of uric acid in the volume of urine taken. The quantity eliminated in 24 hours can then be calculated. ABNORMAL CONSTITUENTS. Albumen.—In all cases the urine should be clear before applying the tests for albumen. If not clear, it should be filtered. (a) Boiling Test.—About 10 cc. of the clear urine are placed in a narrow test-tube, one drop of acetic or nitric acid is added, and the tube heated over a small A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 331 flame in such a way that the upper portion of the liquid only will be heated. In the presence of albumen the urine will become turbid, more or less so in propor- tion to the amount of albumen present. If the acetic or nitric acid is not added before heat- ing, a turbidity will be produced by the phosphates; this, however, will again disappear upon adding the acid. (1b) The Nitric-acid Test.—About 2 cc. of pure ni- tric acid are placed in a test-tube, and the tube being inclined to one side, the urine is carefully run down the side of the tube so that it will float upon and not mix with the acid. An opaque-white zone will appear at the line of contact of the two liquids, if albumen is present. A mixture of nitric acid one volume, and saturated solution of magnesium sulphate five volumes, is some- times used instead of pure nitric acid in the above test, and is used in the same way. (c) Ferrocyamde-of-potassium Test.—A small portion of the urine is acidulated with acetic acid, and filtered if much of a precipitate forms. This acidulated urine is then floated on a solution of potassium ferrocyanide. A white precipitate appears if albumen is present. This is a very delicate and reliable test; peptone, mucin, or alkaloids are not precipitated by it. This is known as Bddeker’s Test. (d) Picric-acid Test.—A cold saturated solution of picric acid may be used in the same way as the nitric acid—by contact. A white zone appears at the line of contact. Alkaloids, mucin, peptones, and urates are, however, precipitated as well as albumen in this A TEXT-BOOK OF VOLUMETRIC ANALYSIS. test, and the solution should be heated to redissolve these. {e) Sodium-tungstate Test.—The reagent is made by mixing equal parts of a cold saturated solution of sodium-tungstate and citric-acid solution. This is a very delicate test, and is applied in the same way as the nitric acid and the above. Peptones, alkaloids, mucin, and urates are also precipitated by this reagent, but these are redissolved upon boiling. if ) Potassio-mercurie-iodide Test, or Tanret's Test,— The reagent is prepared as follows: Mercuric chloride, L 35 gms.; potassium iodide, 3.32 gms.; acetic acid, 20 cc.; distilled water, 80 cc. The two salts are separately dissolved in water, and then the solutions mixed and the acetic acid added. This solution is also used by the contact method. It is very delicate, detecting 1 part of albumen in 20,000 parts of urine. It is neces- sary to heat in order to dissolve the alkaloids, mucin, and peptone, which are precipitated together with the albumen. (g) Acidulated-brine Test.—The reagent is made by adding one fluid ounce of hydrochloric acid to a pint of a saturated solution of common salt and filtering. It is used as follows: The solution is heated to boil- ing, and the urine added by the contact method. A white zone appears at the line of contact if albumen is present. Peptone, alkaloids, etc., are not precipitated by this reagent. The Quantitative Estimation of albumen is of great importance, but comparative tests are, as a rule, suffi- cient. An easy comparative test is to heat a given quantity of urine in a test-tube, add a few drops of A TEXT-BOOK OF VOLUMETRIC ANALYSIS, nitric acid, and set aside for about twelve hours, and then note the volume occupied by the pre- cipitated albumen. This is generally spoken of as volume per cent, and has no relation to actual percentage. More accurate results are obtained with Esbach’s Albuminometer. This is a gradu- ated glass tube (Fig. 32). Fill the tube to U with the urine, then to R with the reagent. Close the tube with a rubber stopper, shake, and set aside for 24 hours. Then note the height of the precipitate, as indicated by the graduations. Each of the numbered divi- sions represents a gramme of albumen in 1000 cc. of urine. The reading should be taken Fig. 32. at the middle of the albuminous surface. The reagent: Picric acid, logms.; citric acid, 20 gms.; water, 1000 gms. Blood.—A small quantity of the urine is mixed in a test-tube with an equal volume of a mixture of freshly prepared tincture of guaiac and spirit of turpentine, which has been exposed to the air for some time. If blood-coloring matter is present the mixture assumes an indigo-blue color, the rapidity of formation of which depends upon the amount of blood-coloring matter present. Pus, saliva, and salts of iodine also give a blue color with this test ; but it appears only after a con- siderable lapse of time, and is seldom likely to mislead. Instead of the spirit of turpentine, peroxide of hydro- gen may be used. Pus.—The presence of pus is easily revealed by the microscope. Urine containing pus is always turbid to the naked eye, and deposits a white or greenish-white sediment, 334 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. which resembles urates or earthy phosphates. If heated the sediment does not disappear—difference from urates, neither is it dissolved by dilute acids— difference from earthy phosphates. It dissolves, how- ever, in strongly alkaline solutions, giving a gelatinous, ropy liquid. Pus effervesces with hydrogen peroxide. Sugar.—{a) Bismuth Test.—A few cc. of urine are placed in a test-tube, and an equal volume of sodium- hydroxide solution and a little bismuth subnitrate ; mix well, and boil for a few minutes. A black precipi- tate is produced if sugar is present. If albumen is present it must be removed before ap- plying the test, as it is decomposed by boiling with the alkali, forming a black sulphide of bismuth. {h) Nylander s Test is a modification of the above. A solution is made of bismuth subnitrate 2 gms., Ro- chelle salt 4 gm., sodium hydroxide 8 gms., and dis- tilled water 100 cc. Heat the urine to boiling, and add a few drops of this alkaline solution of bismuth, continuing the boil- ing. If sugar is present, the mixture turns black. This is a very delicate test, but as in the previous one, any albumen must be removed. (,c) Moore's Test.—Add one part of liquor soda to two parts of urine, and boil. If sugar is present the urine will become blackish brown. Albumen must be removed before applying the test. id) Picric-acid Test.—About 5 cc. of the urine are mixed with half as much of picric-acid solution and about 2 cc. of liquor potassa, and boiled. A dark mahog- any-red color is developed in the presence of sugar. Albumen will cause turbidity, but will not interfere with the test. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 335 (e) Trommers Test.—5 cc. of urine are mixed in a test-tube with one half of its volume of liquor soda, and one or two drops of a solution of CuS04 (1-10). In the presence of sugar a clear, deep-blue color is ob- tained. Heat the solution now almost, though not quite, to boiling. At first a greenish then a yellow turbidity forms, which rapidly changes to a reddish- yellow color, and precipitates red cuprous oxide. An excess of the copper solution should not be used. (f) Haines' Test.—The reagent used is a solution of copper sulphate in a mixture of equal parts of glyce- rine and water. To about 5 cc. of urine add a few drops of this re- agent, and then add sodium-hydroxide solution until the liquid assumes a deep-blue color. The mixture is then gradually heated to boiling. If sugar is present the color changes to yellow, and finally brick-red. (g) Indigo-carmine Test.—The reagent is made by mixing 1 part of dried commercial extract of indigo with 30 parts of pure dry sodium carbonate. The test: Add enough of this powder to 5 cc. of the urine to give it a transparent-blue color, and heat to boiling. If sugar is present, the color changes to violet, cherry-red, and finally yellow. On gently agi- tating the tube the colors appear in the reversed order. {h) Molisch's Test.—Put 1 cc. of the urine in a test- tube, add 2 cc. of a saturated solution of alpha-naph- thol, mix well, and then add an excess of sulphuric acid, A deep violet color is produced if sugar is present. On dilution with water a blue ppt. occurs. Thymol or menthol may be used instead of naph- thol. The color then produced is deep red. Quantitative Estimation.—This is generally effected 336 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. by the use of Fehling’s solution. The process is de- scribed on page 259. By Fermentation.—This is performed by adding a small quantity of yeast to a certain volume of urine and setting aside for about 24 hours. As the sugar is decomposed the specific gravity of the urine becomes less. Therefore by taking the specific gravity of the urine before and after fermentation a fairly accurate estimation of the sugar present may be made, provided the quantity be not less than 0.5 per cent. Each de- gree of the urinometer indicates 0.219 per cent, of sugar. If the specific gravity of a sample of urine is found to be 1032, and after subjecting it to fermentation it is 1022, the quantity of sugar present in the sample is 10 times 0.219 = 2.195, Estimation of Sugar by Dr. Einhorn’s Fermen- tation Saccharometer.—Take one gramme of com- mercial compressed yeast (or T of a cake of Fleisch- mann’s yeast), shake thoroughly in the graduated test-tube with 10 cc. of the urine to be examined. Then pour the mixture into the bulb of the saccharom- eter (Fig. 33). By inclining the apparatus the mix- ture will easily flow into the cylinder, thereby forcing out the air. Owing to the atmospheric pressure the fluid does not flow back, but remains there. The apparatus is to be left undisturbed for twenty to twenty-four hours in a room of ordinary temperature. If the urine contains sugar, the alcoholic fermenta- tion begins in about twenty to thirty minutes. The evolved carbonic-acid gas gathers at the top of the cylinder, forcing the fluid back into the bulb. On the following day the upper part of the cylinder is filled with carbonic-acid gas. The changed level of A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 337 the fluid in the cylinder shows that the reaction has taken place, and indicates by the numbers—to which it corresponds—the approximate quantity of sugar present. If the urine contains more than one per cent of sugar, then it must be diluted with water before being tested. Diabetic urines of straw color and a specific gravity of 1018—1022 may be diluted twice ; of 1022-1028, five times; 1028-1038, ten times. The original (not diluted) urine contains in propor- tion to the dilution two, five, or ten times more sugar than the diluted urine. Fig. 33. 338 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. In carrying out the fermentation test it is always recommendable to take, besides the urine to be tested, a normal one, and to make the same fermentation with it. The mixture of the normal urine with yeast will have on the following day only a small bubble on the top of the cylinder. That proves at once the efficacy and purity of the yeast. If there is likewise in the suspected urine a small bubble on the top of the cylinder, then no sugar is present; but if there is a much larger gas volume, then we are sure that the urine contains sugar. Test for Bile.—(a) Oliver s Test.—Dissolve 2 gms. of fresh peptone (Savory & Moore’s Pulverized), 0.25 gm. salicylic acid, and 2 cc. of 33$ acetic acid in water to make 200 cc. The solution should be rendered perfectly clear by filtration. The urine should also be clarified by filtration, and diluted to a specific gravity of 1008. One cc. of this urine is added to 3 cc. of the above reagent. If bil- iary salts are present a distinct opalescence at once appears, which becomes more intense in about five minutes. This opalescence will be more or less dis- tinct in proportion to the quantity of bile present. (b) Gmelins Test.—2 or 3 cc. of partially decomposed yellow nitric acid are placed in a test-tube, and an equal volume of the urine is cautiously poured on top. In the presence of bile pigments a play of colors will appear, beginning with green, then passing through blue, violet, red, and yellow. The nitric acid may be prepared for this test by adding a fragment of zinc to ordinary nitric acid. (c) Pettenkofer s Test.—Mix equal parts of urine and A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 339 sulphuric acid, add one drop of simple syrup, and apply a gentle heat. The color will change from cherry-red to purple if biliary acids are present. (d) Ultzmanris Test.—s cc. of urine are mixed with 2 cc of a strong solution of KOH (1-3) and then an excess of pure HCI added. The mixture will become emerald-green if biliary pigments are present. (e) Tincture-of-iodine Test.—A few drops of iodine tincture are floated upon the surface of the urine. If biliary pigments are present, there will appear at the line of contact of the two liquids, after a few minutes, a beautiful emerald-green zone. URINARY DEPOSITS. Chemical Examination.—Draw off a portion of the sediment with a pipette or glass tube, and transfer to a watch-glass or small test-tube. Dissolves on heating urine. Ammonium urate. White Sol. in NIbOH Cystine. Deposit. ■4 f Soluble in acetic acid, Insoluble on heating. j Earthy Phosphates. Insol. in NH4OH, -J Insoluble in aceiic j acid, Calcium oxa- ( late or oxalurate. Gelatinizes in NH4OH.. .Pus (see above). f Visibly crystalline (red) Uric acid. { Pale easily soluble by heat Urates. Deposit. ■{ Amor- J Deep colored, slowly soluble by heat, Acid urates phous. | wi th uroerythnn. b Red, insoluble by heat, alkalies or acids. Blood. Microscopical Examination.—With a clean pipette draw off a small portion of the sediment, transfer to a clean glass slide, and examine with a |--in. or |An. ob- jective. A cover glass may be dispensed with, 340 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. Small granules with spicules on larger granules ( light — Sodium urate. Deposit Vanishes on adding KOH or-l is Amor NaOH ( dark = Ammonium urate. phous. Permanent, adding KOH or NaOH Calcium phosphate (rare). Globules, strongly refracting light Fat. f Reddish, cross, or whetstone shape, or in groups Uric acid. _T . 1 Regular octahedra, envelope-shaped, Calcium oxalate. Ann,e <1 Hexagonal plates, soluble in NH4OH (white) Cystine. De- Bundles of needles*- crossing each posit I other Ty rosin. is Large prisms, soluble in acetic acid (coffin-lid Crys-1 shape), Ammon, magnesium phosphate. tal- Brown, double spheres, spiculated, Urate of ammo- line. niutn. Alkaline Urine. ‘ Club-shaped crystals, single or in groups, Calcium phosphate. Double spheres, radiated structure, soluble in acetic acid, with effervescence, Calciutn carbonate (rare). Double spheres, insoluble in acetic acid, Calcium oxalurate (rare). r Double pheres, yellow or red, radiated Uric acid. Red or yellow disks, biconcave ; sometimes irregular in out- line, Blood cells. Cellu- lar Ele- ments Cranulated corpuscles [Albumen nt Pus, With dilute acetic acid V Mucus £orpuscleSt show 3 to 5 nuclei. ) r Round, conical, or flat cells with one nucleus, Epithelium from urinary tract. Tadpole shape, with long tail Spermatozoa. Cylinders, parallel margins, clear, granular, or containing epithelial cells as blood cells... Casts of uriniferous tubules. Fungi, yeast, hairs, threads, etc., etc.. . .Extraneous matters. —From Bartley s Medical Chemistry. A little experience in the microscopical examination of urinary sediments will usually enable one to readily recognize the various forms, and thus obviate the neces- sity for a chemical examination. Analysis of Urinary Calculi.—The following table will show at a glance the compositions and methods of proving the various calculi: A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 341 i. Calculi, fragments of which, heated to redness on platinum, entirely burn away. Name. Physical characters. Chemical Characters. Uric acid, CiN4H403 Brownish red ; smooth Insoluble in water; soluble in KHO or tuberculated; con- by heat, but evolves no NHS; dis- centric laminae (com- solves with effervescence in HNG3 mon). and the residue on evaporating the solution is red and gives the mu- Ammonium urate Clay-colored ; usually re Aid test. Soluble in hot water ; soluble in smooth, and rarely heated KHO, evolving NH3. Be- with fine concentric haves with HNOs like uric acid. Cystine, C3H7NS02 laminae (uncommon). Brownish- yellow, Insoluble in H20, alcohol, and ether. semi-transparent and Soluble in NH4HO, and depositing, crystalline (very un- when allowed to evaporate spon- common). taneously, hexagonal plates. When Xanthin, C6H4N402 heated, gives off odor of CS2. Pale polished brown Soluble in KHO ; soluble in HN03 surface (very un- •without effervescence,and the solu- common). tion leaves on evaporation a deep- yellow residue. 2. Calculi, fragments of which, heated to redness on platinum, do not burn away. Name. Physical Characters Chemical Characters. Calcium oxalate, Deep brown, hard and Insoluble in acetic acid, but soluble mulberry calculus. CaC204 rough ; thick layers without effervescence in HC1 ; (common). heated to redness, it is converted into CaCOj , which dissolves with effervescence in acetic acid, and the solution gives a white precipitate with (NH4)2C204. Heated strong- ly before the blowpipe, CaO re- mains, which, when moistened, is Tricalcium phos- Pale brown, with regu- alkaline to test-paper. Infusible before the blowpipe, and phate, bone-earth lar laminae (uncom- residue, when moistened, is not al- calculus, Ca3(P04)2 mon). kaline. Soluble in HC1, and the solution gives a gelatinous precipi- Magnesium ammo- White, brittle, crys- tate with excess of NH4HO. Fusible with difficulty before the nium phosphate. talhne, with an un- blowpipe, evolving NHS, and res- triple phosphate even and not usually idue not alkaline. Soluble in HC1, calculus, MgNH4P04 Mixed phosphates of Ca, Mg, and NH4, laminated surface and solution gives white crystal- (uncommon). line precipitate with NH4HO. White, and rarely lam- Readily fusible before the blowpipe. inated. Soluble in acetic acid, and solu- Jusible calculus tion gives a white precipitate with (NH4)2C50„ and the filtrate from that precipitate gives a white pre- cipitate with excess of NH4HO. -From Muter's Analytical Chemistry Part 111. GASOMETRIC ANALYSIS. CHAPTER XXXIV. THE NITROMETER. FOR general gas analysis, and for the rapid estima- tion of such substances as ethyl nitrite, hydrogen peroxide, urea, bleaching-powder, manganese peroxide, etc., an instrument called the nitrometer is used. The apparatus in its simplest form is shown in Fig. 34. It consists of a measuring-tube (A) graduated in cc., and fitted at the top with a three-way stop-cock (D) and a glass cup or funnel (t7). The stop-cock is so arranged that according to the way in which it is turned it will dis- charge the contents of the cup either into the tube below or out in the waste- opening (E); or it will discharge the contents of the graduated tube into the waste-opening. The graduated tube generally has a capacity of 50 cc., and is graduated in Fig. 34. cc., the graduation beginning at the top. This measuring-tube is connected by means of a strong 342 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 343 flexible india-rubber tube with an ungraduated tube (A?) called the control-tube, pressure-tube, or level-tube. Both tubes are held in clamps upon a stand. With this apparatus gases can be rapidly and accu- rately measured at definite temperature and pressure. In measuring the gas the instrument is filled with some liquid in which the gas is insoluble—generally mercury. In many cases a saturated solution of salt may be used. Suppose we fill the instrument with mercury in such quantity that when the stop-cock is opened and the control-tube raised, the mercury will rise as far as the top, and about two inches in the control-tube. T-he top is now closed, the control-tube lowered, and a little carbonic-acid gas admitted through {£). The top is then again closed, and the instrument al- lowed to stand until its contents have acquired the temperature of the room. A centigrade thermometer suspended to the stand will then give the temperature of the gas. The control-tube is now raised or lowered so as to make the level of the liquid in both tubes the same. This makes the pressure in the tube the same as the atmospheric pressure outside, and by referring to a barometer standing near this pressure is ascertained. We now have a definite volume of the gas at a known temperature and pressure. It now only remains to read off the volume of the gas, and correct it to the normal temperature and pressure by Charles’ and Boyle’s laws, respectively. dhe normal temperature and pressure is o° C. and /60 mm. pressure. The weight of the gas in grammes may then be cal- 344 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. ciliated from its volume by multiplying the number of cc. at the normal temperature and pressure, by the weight of one cc. of the gas in grammes. This weight may be found as follows: 1000 cc. of hydrogen at normal temperature and pressure weigh 0.0896 gm. One cc. of H then weighs 0.0000896 gm. One cc. of oxygen weighs 16 times as much, and one cc. of nitrogen weighs 14 times as much. Therefore, by multiplying the weight of one cc. of H by the atomic weight of an elementary gas, or half the molec- ular weight of a compound gas, the weight of one cc. of that gas is obtained. According to the law of Charles, the volume of a gas under constant pressure varies directly with the ab- solute temperature. All gases expand or contract by of their volume for each centigrade degree of temperature, increased or decreased. We may regard a gas at o° C. as having passed through 2730 C. In other words, 273° below zero must be regarded as the absolute zero, and o° C. as 2730 ab- solute temperature. Thus the absolute temperature centigrade is the ob- served temperature -(- 2730. Example.—A given volume of oxygen gas at 150 C. measures 20 cc. What will it measure at o° C. ? o + 273 X 20 273 X 20 0 . -o~ o or -'-So—= 18.95 cc. A ns. 15+273° 288° y Boyle’s Law.—The volume of a confined gas is in- versely proportional to the pressure brought to bear upon it. That is, the less the pressure the greater the volume, and vice versa. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 345 Rule.—Multiply the observed volume by the observed pressure, and divide by the normal pressure. Example.—A given volume of gas at 750 mm. press- ure measures 20 cc. What will it measure at 760 mm. (the normal pressure)? 750 X 20 cc. = 19.73 cc. Ans. Now let us take an example in which both laws are involved. A given volume of oxygen at 150 C. subjected to a pressure of 750 mm. measures 20 cc. What will it measure at the normal temperature and pressure?— i.e., o° C. and 760 mm. In the first example we find that 20 cc. of oxygen at 15° C. will measure at o° C. 18.95 cc. Then 750 X iB-95 cc. = 18.70 cc. A ns. Now to find the weight of this volume of oxygen we proceed as follows: 1 cc. of H weighs 0.0000896 gm.; 1 cc. of O weighs 16 X .0000896 = 0.0014336 gm.; 18.70 cc. of 0= 18.70X0.0014336 gm., or 0.02680832 gm. A TEXT-BOOK OF VOLUMETRIC ANALYSIS. CHAPTER XXXV. ASSAY OF SPIRITUS ATHERIS NITROST. Spirit of Nitrous Ether.—This is an alcoholic solu- tion of ethyl nitrite (C2H6NO2 = 74.97), yielding when freshly prepared and tested in the nitrometer not less than 11 times its own volume of nitrogen dioxide (NO = 29.97), U. S. P. When nitrites are mixed with an excess of KI and acidulated with H2S04, iodine is liberated, and all the nitrogen of the nitrite is evolved in the form of NO, as shown in the equation 2C.H.NO, + 2KI + 2H2S04 149-74 = 2CsH6OH + 2KHS04 + I 2 + NO. 59-94 The process of the U. S. P. is conducted as follows: Open the stop-cock of the measuring-tube, raise the control-tube, and pour into the latter a saturated solu- tion of NaCl until the measuring-tube, including the bore of the stop-cock, is completely filled. Then close the stop-cock and fix the control-tube at a lower level. Now introduce into the funnel at the top of the meas- uring-tube 5 cc. of recently prepared spirit of nitrous ether, open the stop-cock, and allow the spirit to run into the nitrometer, being careful that no air enters at A TEXT-BOOK OF VOLUMETRIC ANALYSIS. the same time. 10 cc. of potassium iodide T. S. are now added in the same manner, and followed by 10 cc. of normal sulphuric acid V. S. Effervescence takes place immediately, and if the tube be vigorously shaken at intervals the reaction will complete itself in ten minutes. The control-tube is now lowered so as to make the level of the liquid in both tubes the same, and the volume of the gas in the graduated tube read off. According to the U. S. P., the volume of NO gener- ated at the ordinary indoor temperature (assumed to be at or near 250 C., yy° F.) should not be less than 55 cc. if 5 cc. of the spirit are taken, corresponding to about 4 per cent, of pure ethyl nitrite. Sodium-chloride solution is used in the above assay, because owing to its density the spirit will float on top, and the gas evolved will not dissolve in it. *At the same time the expense of using mercury is saved. It is important that no air be allowed to get into the measuring-tube, because this would convert the NO into a higher oxide of nitrogen, which would dissolve in the salt solution, and thus vitiate the result. If it is desired to ascertain the percentage of ethyl nitrite present in a sample of spirit of nitrous ether which is either above or below the U. S. P. standard, it is necessary to find how much ethyl nitrite each cc. of NO represents, under a definite degree of tempera- ture and pressure. It is generally convenient to correct the volume of gas evolved at higher temperatures to its correspond- ing volume at o° C. The calculations involved are fully explained below. Example.—s cc. of spirit of nitrous ether (sp. gr. 0,840) 348 A TEXT-BOOK OF VOLUMETRIC ANALYSIS. are treated in a nitrometer, and the NO evolved meas- ures 55 cc. The temperature at which the operation is conducted is 250 C, and the atmospheric pressure normal. What per-cent, of ethyl nitrite is present in the sample ? By consulting the equation given above, it will be seen that one molecular weight of NO = 29.97 is evolved from one molecular weight of ethyl nitrite, 74.87. Now reduce the volume of the gas liberated at 250 C. to its corresponding volume at o° C. Thus 273° + 25° : 55 :: 273° +o°: x. x- 50.4 cc. Thus the gas evolved from 5 cc. of the spiritus aetheris nitrosi, measured at o° C., is 50.4 cc. The next step in the calculation is to find how much ethyl nitrite each cc. of the evolved NO represents. One litre of hydrogen at o° C. and normal pressure weighs 0.0896 gm. By multiplying this weight by half the molecular weight of NO, the weight of 1000 cc. of the latter gas is obtained ; this will be found to be 1.3423. Now if 1.3423 gm. of NO measures 1000 cc., 29.97 gms. will measure 22325.24 cc. 1.3423 : 1000 ;: 29.97 :x. x 22328.24. Then if 22328.24 cc. of NO are evolved by, and con- sequently represent, 74.87 gms. of ethyl nitrite, as the equation shows, 1 cc. of NO will represent 0.0033529 gm. of pure ethyl nitrite. Now, since in the above example 50.4 cc. of gas were A TEXT-BOOK OF VOLUMETRIC ANALYSIS. 349 evolved at o° C., the 5 cc. of spirit of nitrous ether examined must contain 50 4 X 0.0033529 gm- = 0.1689912 gm. of pure ethyl nitrite. In order to determine the percentage strength, the weight of the spirit taken must be known. This may be found by multiplying the measure by the specific gravity, 5 cc. X 0.840 = 4.2 gms. Then 4-2 gms. : 0.1689912 gm. :: 100 :x. x 4 360 Brazil-wood T. S n, 368 cochineal T. S xxs 368 corallin T. S 355 eosin, and its solution n, 366 fluorescein, and its solution xx, 366 gallein 366 lacmoid, and lacmoid paper 367 litmus 10, 360 methyl-orange 363 test solution 11, 364 phenacetolin 368 phenolphthalein 362 rosolic acid 365 test solution 10, 363 test solution 10, 366 turmeric tincture... 11, 369 paper 369 Indigo-carmine test for sugar . . 335 solution 243 Indirect oxidation, analysis by 161 Interpretation of results of. water analyses ... ... 224 386 INDEX Instruments, cleaning of 27 PAGE graduation of 15 correct reading of 28 lodide of iron, saccharated 116 syrup of. 112 potassium 105 by sulphocyanate method 114 sodium 107 Personne’s method 106 strontium 108 lodine 175 zinc io3 decinormal V. S. of 162 tincture of 177 lodometric method for estimating hydrogen dioxide 200 lodometry 172 Ipecac root 306 fluid extract of .... 304 Iron and ammonium citrate 188 sulphate 192 tartrate 188 potassium tartrate 188 quinine citrate. , 189 strychnine citrate 191 soluble. 191 acetate, solution of 196 bromide, syrup of 117 carbonate, saccharated. 138 chloride 184 solution of 185 citrate 186 tincture of 186 hypophosphite 149 solution of ... 187 iodide, saccharated 116 syrup of 112, 114 nitrate, solution of 197 phosphate, soluble ... 188 pyrophosphate, soluble 194 reduced 143 INDEX 387 PAGE Iron, saccharated carbonate 138 iodide , 116 salts (ferric) 183 (ferrous) 128 estimation of, by K2Cr207 136 sulphate 140-145 2KMnO4 141 subsulphate, solution of 198 syrup of bromide 117 tersulphate, solution of. 199 iodide 112, 117 valerianate xgg wire, standardization of dichromate and permanganate solutions with 132 Kilogramme, the xg Kingzetl’s method for estimating hydrogen dioxide 200 Koppeschaar’s solution 266 Labarraque’s solution igx Lacmoid 367 Paper 367 Lactate of strontium Lactic acid... Lactometer 3IX Laudanum 300 Law, Boyle’s 344 Lead subacetate solution 124 Charles’ 344 Lemon-juice 77 water 126 Lime, chloride of X7B chlorinated 178 valuation of, by arsenous acid 180 Liquor acidi arsenosi 164 calcis go juice. 77 saccharatus gx ferri acetatis. 196 chloridi *. ... .. 185 388 INDEX. Liquor ferri citratis 187 nitratis 197 PAGE subsulphatis 198 iodi compositus 176 tersulphatis 199 plumbi subacetatis 124 potassse.. 44 sodae 45 arsenitis 165 Lithium benzoate 63 chloratae 181 bromide 101 carbonate 51 citrate 59 Litmus tincture 11, 360 salicylate 66 Litre, the. 15 flask 20 Loss on ignition 206 Lugol’s solution 176 Lunar caustic 123 Magnesia mixture 84 Magnesium salts 95 Malt extracts, diastasic value of 281 Mandarin-orange 363 Mayer’s solution 292 Measuring-flask 20 Melting-points of fats 251 Meniscus 28 Methyl-orange 363 test solution 11, 364 Milk 309 Adam’s method for fat in 314 adulterations of 313 ash 317 average composition of 309 calculation method for fat in 316 of per cent of added water 317 composition, average ~... .. 309 INDEX 389 Milk fat 214 Werner-Schmid method for 315 PAGE lactose 2iS milk sugar 2!8 reaction of 210 specific gravity of 2io total proteids of 2iB Mineral acids in vinegar 75 solids in 313 Mitigated caustic 123 Mohr’s burette xg Molisch’s test for sugar in urine 335 foot-burette xg Monsel’s solution xgB Moore’s test for sugar in urine 334 Moulded caustic 122 Murexid test for uric acid 230 Muriatic acid 78 Naphthalamin-hydrochlorate solution 214 Naphthylammonium-chloride solution 214 Nessler’s solution 207 Neutralization, analysis by 2& Nitrate of barium g2 iron, solution. xgy potassium solution 212 silver 121 diluted 123 moulded 123 Nitrates in water 211 standard solution of g7 Nitric acid in nitrates 350 nitric acid in 350 Nitrite of amyl 34g ethyl 346 sodium 250 Nitrites in water 214 Nitrite, standard solution of, for water analysis 215 Nitrogen, as ammonia 211 nitrates 211 390 INDEX PAGE Nitrogen, as nitrites .... 2x4 Nitrometer, the 342 estimation of carbonates with 352 Nitrous ether 346 Normal solutions 4-S hydrochloric acid V. S 40 oxalic acid V. S 39 potassium hydroxide V. S 71 sodium carbonate V. S 8g sulphuric acid V. S 41 hydroxide V. S 69 Nux-vomica extract 296 fluid extract . 298 tincture 298 Nylander’s test for sugar in urine 334 Oil in emulsions, estimation of 252 Ointments, estimation of fat in 252 Oleic acid 246 Oliver’s test for bile in urine 338 Opium 301 extract of 298 tincture of 300 Orange, methyl 363 Organic and volatile matters in water 206 Oxalic acid 158 salts of the alkaline metals. 54 decinormal solution of 40 normal solution of 39 Oxide of silver 123 Oxidation, analysis by 127 Oxidimetry 127 I indirect, analysis by r6t Oxygen-consuming power of water 216 Pancreatic extracts, diastasic value of ; 281 Pepsin 275 valuation of 277, 278 Percentages, how found 31 Permanganate of potassium, alkaline solution of. 208 INDEX, 391 PAGE Permanganate of potassium, centinormal V. S. of 131 decinormal V. S. of .... 131 Peroxide of barium 157 Pettenkofer’s test for bile in urine 338 hydrogen 152-154, 200, 357 Phenacetolin 368 Phenol 266-272 Phenolphthalein 362 solution of 363 Phosphates in urine 327 water 2ig Phosphoric acid 82 by Stolba’s method 84 Picric-acid test for sugar in urine 334 as ammonio-magnesian phosphate 84 Pipettes 2I Porrier’s orange 111 353 nipple 22 Potassa solution of Potassio-ferric tartrate jgg Potassium acetate 5j and sodium tartrate 37 arsenite, solution of bicarbonate. 4g bitartrate 58 bromide ior bichromate, decinormal V. S. of 129 carbonate 48 chloride 109 chromate, solution of 11, 206 citrate 60 cyanide , 120 dichromate, decinormal V. S. of 129 ferricyanide T. S ix tests for the purity of 129 hydroxide, centinormal V. S. of 71 normal V. S. of 69 iodide 105 Personae’s method 106 INDEX, PAGE Potassiurti nitrate solution, for water analysis 212 permanganate, centinormal V. S. of 131 decinormal V. S. of 131 standardization of, with iron 132 oxalic acid ... 133 solution of, for determining tne oxy gen-consuming power of water 217 sulphocyanate V. S 113 sulphite ... 167 Precipitation, analysis by 96 tartrate 55 Preservation of alkaline solutions, bottle for 69 Pus in urine 333 Pyrophosphate of iron, soluble 194 Qualitative analysis 1 Quantitative analysis x Quinine, in citrate of iron and quinine 189 Reaction of milk 310 Reading of instruments 28 urine 322 Reagents and test solutions 369 Reduced iron 143 Reduction, analysis by 172 Residual titration g Resin, estimation of, in drugs 306 Resorcin-phthalein 366 Results, interpretation of 224 Retitration g Rochelle salt 57 Rosolic acid 365 solution of ii, 366 Saccharated ferrous carbonate 138 iodide 116 Salicin 308 Salicylate of lithium 66 Salt solution, acidified 244 sodium ... 67 INDEX 393 Saturation, analysis by 38 PAGE Semi-normal solutions. g Separator 293 Set solution 4 Silver carbonate test, for uric acid 330 estimation of, by sulphocyanate 124 nitrate 121 diluted 123 moulded... 123 solution, for water analysis 206 Soap, analysis of 248 solution, for determining hardness of water 221 Soda. ac. 45 solution of 45 Sodium acetate 52 and potassium tartrate 57 benzoate 64 bicarbonate 50 bisulphite. !68 bromide IQ2 carbonate 49 exsiccated 50 solution, for water analysis 208 chloride . .. no normal V. S 89 decinormal V. S 122 hydroxide 45 purification of X 22 hypophosphite 151 normal V. S 71 hyposulphite .. xgg iodide, ..■• ... .. 107 nitrite 350 salicylate 57 solution 215 sulphite xfifi thiosulphate x5B Solution, alkaline permanganate 208 tungstate test for albumen 331 ammonium chloride 208 394 INDEX Solution, chlorinated soda 181 PAGE ferric chloride 185 citrate *BB nitrate 197 subsulphate igB tersulphate. , igg Fowler’s 165 Labarraque’s 181 Lugol’s ; 176 Monsel’s igB silver nitrate, for water analysis 206 decinormal g7 soap, for estimating hardness of water 221 sodium carbonate, for water analysis 208 normal V. S 8g subsulphate of iron 198 nitrite 215 sulphanilic acid 214 tersulphate of iron xgg Solutions, centinormal 8 decinormal 8 empirical 9 normal 4-8 semi-normal 9 “set” 4 standard 4 Soxhlet’s extraction apparatus 253 “ standarized ” 4 Specific gravity of milk 310 urine 324 Spirit of ammonia 47 aromatic 352 nitrous ether 346 Squibb’s urea apparatus 355 Standard solutions 4 Standards for determining the quality of water 231 Starch, estimation of 255-258 Statement of water analysis 224 Strontium bromide 103 iodide 108 INDEX. 395 Strontium lactate... 94 PAGE Strychnine, in citrate of iron and strychnine 191 Subacetate of lead solution.. , 124 Sugar in urine 334 bismuth test for 334 Einhorn’s saccharomeler lest 336 Haines’ test 336 indigo-carmine test 335 Molisch’s test 334 Moore’s test 334 Nylander’s test 334 picric-acid test 334 quantitative estimation of 335 Trommer’s test 335 Support for burettes 25 Sulphanilic-acid test solution 214 Sulphates in urine 327 gravimetric estimation of 328 Sulphocyanate method for ferrous salts 114 volumetric estimation of 328 solution Ix 3 Sulphite of potassium x6y sodium. 166 Sulphuric acid. 86 aromatic 87 Sulphurous acid 165 diluted 87 Syrup of ferrous bromide. 117 i0dide.........; Ix 2. 117 hydriodic acid in lime gx Table, acetic acid 75 for ascertaining the percentage of alcohol 240 correcting the sp. gr. of milk, according to the temper- ature 312 of the elementary substances xvii substances estimated by precipitation 125 substances, which may be estimated by oxidation with K2Cr207 or 2KMn04 x6o 396 INDEX pack Table, of substances, estimated by iodine 171 sodium thiosulphate 201 showing behavior of some alkaloids with indicators 289 showing approximate normal factors, etc., for the acids.. 88 showing approximate normal factors, etc., for the alkalies, alkaline earths, and acids 35 showing approximate normal factors, etc., for the organic salts of the alkalies 68 showing factors for various alkaloids when titrating with acid or alkali 200 20 showing composition of the milk of different animals.. .. 310 showing average composition of normal urine 323 showing contraction and expansion of water at various temperatures.. 16 showing relationship of the lactometer indication to the sp.gr 311 showing volume of .001 gm. of C02 at various tempera- tures 237 Tannic acid, estimation of 242, 243 Tannin, estimation of 242, 243 Tartrate of antimony and potassium 169 iron and ammonium 188 potassium 188 potassium 55 solution, alkaline, for sugar 259 and sodium 57 Tartrates, estimation of 54 Tartar emetic 169 Tartaric acid 87 Tersulphate-of-iron solution 199 Test-mixer 21 Test solutions and reagents 369 Thiosulphate of sodium 168 Tincture of iodine 117 decinormal V. S. of 173 turmeric 369 test for bile in urine 339 Titrate, to 9 Titrated solution 4 INDEX 397 Titration, backward g PAGE Total acidity of urine 328 residual g proteids in milk 318 solids, and added water, in milk 313 in urine 325 Trommer’s test for sugar in urine 335 Tropseolin D 366 Turmeric paper 369 tincture 11, 369 Ultzmann’s test for bile in urine 339 Urates 329 Urea, estimation of 329 by Doremus’ ureometer 353 Squibb’s urea apparatus 355 Ureometer 333 gas tube 354 Uric acid 329 qualitative tests for 330 quantitative estimation of . 336 murexid test for -. 330 Urinary calculi, analysis of , 340 silver-carbonate test for . 330 deposits 339 chemical examination of 339 Urine, abnormal constituents of 330 microscopical examination of 339 acidulated brine test for albumen in 332 albumen in 330 detection of, by boiling 330 nitric-acid test 331 ferrocyanide lest 331 albumen in, detection of, by potassio-mercuric-iodide test 331 picric-acid test 331 quantitative estimation of, by Esbach’s albu sodium-tungstate test 332 average composition of 223 minometer * 332 bile in, detection of, by Gtnelin’s lest 33$ INDEX. Urine*, bile in, detection of, by Oliver’s test 338 Pettenkofer’s test 336 PAGE tincture-of-iodine test 339 bismuth test, for sugar in 334 Ultzmann’s test 339 blood in 333 chlorides in 326 fermentation test, for sugar in 336 ferrocyanide test, for albumen in 331 Gmelin’s test, for bile in 338 gravimetric estimation of sulphates in 328 Haines’ test, for sugar in... 335 indigo-carmine test, for sugar in 335 Molisch’s test, for sugar in. •. 335 Moore’s test, for sugar in. 334 murexid test, for uric acid in 330 Nylander’s test, for sugar in 334 nitric-acid test, for albumen in 331 normal ... .. 322 Oliver’s test, for bil in 338 Pettenkofer’s lest, for bile in 338 phosphates in 327 picric-acid test, for sugar in 334 potassio-mercuric-iodide test, tor albumen in 332 albumen in 331 pus in 333 reaction of 322 silver-carbonate test, for uric acid 330 sodium-tungstate test, for albumen in 332 sugar in 324 specific gravity of 324 sulphates in 327 total acidity of 328 solids of 325 Trammer’s test, for sugar in 335 tincture-of-iodine test, for bile in 339 Ultzmann’s test, for bile in 339 urates in 329 urea in 329 uric acid in . 329 INDEX 399 PAGE Urine, volumetric estimation of chlorides in. 226 Urinometer „„ _T , sulphates in. 328 Use of apparatus 2_, Valerianate of iron Valuation of pepsin, Bartley’s method 278 Vinegar ?4 U. S. P. method 277 Volhard’s method for ferrous iodide Xl 2 estimation of mineral acids in. 75 solution IT^ Volume strength of hydrogen dioxide 155 Volumetric estimation of alkaloids 285 instruments, how graduated 15 method, the 2 solutions 4 centinormal 8 decinormal 8 double-normal g normal 4-3 solution of alkaline permanganate 208 seminormal. g arsenous acid, decinormal 181 bromine, decinormal 262 dichromate 129 hydrochloric acid, normal 40 iodine, decinormal 162 mercuric potassium iodide 292 oxalic acid, decinormal 40 N permanganate, 243 normal 39 decinormal 131 potassium dichromate, decinormal 129 hydroxide, centinormal 71 silver nitrate, decinormal 97 normal 69 sodium carbonate, normal 89 chloride, decinormal 122 400 INDEX, Volumetric solution of sodium hyposulphite 173 PAGE thiosulphate 173 Water, albuminoid ammonia in 210, 228 Water, ammonia 46 in 207, 227 analysis of, sanitary 202 free 208 chlorine in 206, 226 collection of sample of 202 color of.. .. 203, 225 hardness 0f.... 219, 224 interpretation of results of analysis of 224 loss on ignition 205 nitrogen as nitrates in 211, 228 nitrites in 214 odor 203, 225 organic and volatile matter in 205 oxygen-consuming power of,. 216 permanent hardness of 220, 224 phosphates in 217 reaction of 204 statement of analysis of 224 suspended matter 204 temporary hardness of 220 total solids in 204, 225 Weights and measures used in volumetric analysis 15 Zinc bromide. ... 104 chloride no iodide 10S