Praetieal I 1 
i UNIVERSITY OF MICHIGAN 
PRACTICAL 
Electro-Therapeutics 
a 
MANUAL 
OF 
Laboratory Experimentation 
FOR 
STUDENTS OF MEDICINE 
BY 
CHARLES K. McGEE, A. 8., 
Instructor in General Chemistry 
in the 
University of Michigan 
AjSTN ARBOR, MICH. 
SHEEHAN & CO., UNIVERSITY BOOKSELLERS 
1890 REGISTER PUBLISHING HOUSE, ANN ARBOR, MICH. PREFACE. 
The successful use of electricity as a therapeutical agent re- 
quires upon the part of the physician a considerable knowl- 
edge of electricity as a pure science and more or less experi- 
ence in the practical handling of electrical apparatus. This 
study of what may be called Electro-Physics must of necessity 
precede the study of Electro-Therapeutics proper. Unfortu- 
nately the subject of Physios has not heretofore received in our 
medical schools that attention which its importance demands 
ad to this cause undoubtedly has been due in large measure 
the long delayed recognition by the medical profession of the 
importance of electricity as a means of treating disease. 
Such recognition is now, however, no longer withheld by 
those who are abreast of the best medical practice of the day 
and the study of electricity as a science, and by the laboratory 
tnethod, is rapidly becoming an absolute essential in the educa- 
tion of the general practitioner. 
In recognition of these facts an optional laboratory course 
in electricity for professional students was several years ago 
established in the University of Michigan. The need of a suit- 
able manual was quickly felt, and in 1884 Professor J. W. Lang- 
ley, by whom the course was organized, published what may be 
°alled the pioneer work in this line of electrical study. 
The natural expansion of the course and the experience ac- 
quired within the last six years calls for a new manual of experi- 
ments. The present book embodies, in substance, much that 
contained in the former one but many changes and additions 
been made. This does not profess to be a complete manual 
laboratory electricity. It is designed for a special class of stu- 
nts who wish to acquire, in a short laboratory course, a knowl- 
■%e of such portions of the science as shall be of the most value PREFACE. 
in the practical employment of electricity in medicine. Accord- 
ingly the briefest outline of only those facts and principles 
which conduce to this end has been given; while, as an aid to 
the student in filling in the outline, many references to two 
standard works—one upon electricity as a pure science, and the 
other upon electricity in its applications to medicine—have 
been made. 
If this little manual shall assist in making the course in 
Electro-Therapeutics a source of still greater profit and pleas- 
ure than it has been in the past, the author will feel that his 
labor has not been unrewarded. 
CHAS. K. McGEE. 
Ann Arbor, March, 1890. CONTENTS. 
PAGES. 
1. Galvanic Batteries, 1 
2. Electric Light Wires, 3 
3. Local Action and Amalgamation 3 
Experiments 1 to 7, 4-5 
4. How to Solder, 5 
5. Rules and Memoranda, 6 
6. The Galvanometer, 8 
7. Rules for Using the Galvanometer, 9 
8. Battery Polarization U 
Experiments 8 to 13 10-11 
9. Prevention of Polarization, 11 
Experiments 14 to 16, 12-13 
10. What Determines the Strength of the Current. Ohm’s Law, 13 
11. Useful Memoranda, 14 
12. The Best Method of Coupling Cells, 10 
13. Electrical Measurements, 18 
Experiments 17 to 25, 17-18 
14. Divided Currents, 20 
Experiments 26 to 31, 18-20 
15. Shunts 20 
Experiments 32 to 34, •. 21 
16. How to use the Electric Light Current, 21 
17. Electrolysis, 23 
18. Corrosion of the Electrodes, 24 
19. Surgical Electrolysis, 24 
20. Polarization of Electrodes 25 
Experiments 35 to 50, 25-29 
21. Galvano-cautery, 29 
Experiments 51 to 61 31-33 
22. Magnetic Effects of the Current 33 
23. The Induction Coil 35 
Experiments 62 to 65 34-35 
24. Magneto-Electric Machines 40 
Experiments 66 to 73 39-40 
25. Electrical Testing 42 
Experiments 74 to 77 42 
26. Problems •' 47 
Experiments 78 to 91 46 
Questions 50 ABBREVIATIONS. 
C—Current. 
G—Galvanometer 
G (1. c.)— Galvanometer, lower coil. 
G (u. c.)—Gah anometer, upper coil. 
E—Electromotive force. 
R—Battery Resistance. 
r—Resistance outside of the battery, 
m. a.—Coupled in multiple arc. 
T.—Thompson’s “Elementary Lessons in Electricity and Magnet- 
ism.” Edition of 1888. Numbers refer to paragraphs. 
B. R.~Beard and Rockwell’s “ Medical and Surgical Electricity.” 
Seventh edition. Numbers refer to pages. PRACTICAL ELECTRO-THERAPEUTICS. 
1. Galvanic Batteries.—For the practicing physician 
the principal source of electricity is the galvanic battery. The 
one great fundamental fact of nature upon which nearly all 
forms of the galvanic cell depend is the following: 
If any two metals, brought into electrical connection by 
simple contact or by a wire, be immersed in any acid, alkali or 
solution of a salt which is capable of corroding either of them 
a current of electricity will flow across the connection from the 
least to the most corrodible of the two metals. The current will 
traverse a completely closed circle or circuit consisting of the 
incorrodible metal, the wire, the corrodible metal and the cor- 
rosive fluid and continue to flow as long as any of the corrodible 
metal is left or until the corroding fluid is exhausted. “ Open- 
ing. the circuit ” at any point, by cutting the connecting wire, 
for example, or by dividing the fluid into two portions by means 
of a non-conducting diaphragm, will cause an immediate ces- 
sation of the current. 
Many different conditions influence the strength and con- 
stancy of the current and many different modifications of this 
simple arrangement of two metals in a corroding fluid have been 
made for the purpose of obtaining as constant and as strong a 
current as possible. Hence has arisen several hundred forms 
of the galvanic cell [See Niaudet’s “Electric Batteries,”] each 
having its own peculiar advantages and disadvantages. A 
knowledge of only about half a dozen different forms is neces- 
sary to the physician. Read up on the following which are of 
importance for the reasons given; 
This is a battery which any physician can easily make in a 
few hours in almost any village in the country and will serve 
admirably as an “emergency battery.” 2 
GALVANIC BATTERIES. 
1. Volta’s Cell.—lmportant as illustrating the simplest 
form of battery and the general principles of the galvanic cell. 
[T. 152, 154, 155, 157, 158, 159,160,166,167,168,169.—8. E. 21, 
22, 23, 26.] 
2. Copper Sulphate Cells. [Daniell’s, Gravity, Saw- 
dust, Etc.]—Important as a standard of electro-motive force 
and for being almost absolutely non-polarizable. Not often 
used in therapeutical work. [T. 170, 176.—B, E. 32,] 
3, Bunsen’s Cell.—Heretofore the most widely known and 
used of all batteries. A powerful, constant, cheap, durable bat- 
tery but not very portable. On account of the labor of setting 
it up and taking it down every time it is used the Bunsen is not 
as convenient a battery as the Bichromate. [T. 171, 172. 
B. E. 34.] 
4. Sulphate of Mercury Cells.—Used to a considerable 
extent in small pocket induction coils. A quite powerful and a 
very compact battery, but the use of the mercury salt renders it 
expensive for any other purpose than to operate small induction 
coils. [T. 175.] 
5. Bichromate or Potash Cells. [Chromic Acid,Grenet’s 
Battery, Etc. ]—A powerful and cheap battery giving a reason- 
ably constant current if not placed upon “ short circuit.” The 
great point in favor of this cell is the readiness with which it 
can be set up and taken down—it being only necessary to lower 
the plates into the fluid before and to withdraw them again 
after using the battery. When the fluid is fresh this cell is 
fully equal to the Bunsen excepting upon circuits of very low 
resistance. Ten to twenty small Bichromate cells, each holding 
one or* two ounces of fluid, make a most excellent battery for all 
kinds or therapeutical work excepting that requiring the elec- 
tro-cautery or the induction coil. Special attention will be 
given to the practical understanding and use of this battery. 
[T. 165.—8. E. 35, 307.] 
6. Sal Ammoniac Cells. [Leclanche, “Diamond Car- 
bon,” Etc.]—This is the only one of the various batteries to be ELECTRIC LIGHT WIRES. 
3 
considered which can be left permanently set up. For this 
reason it is especially suitable for operating door and office 
bells, annunciators, call bells, etc. It polarizes quite rapidly if 
left upon closed circuit for more than a few moments (especi- 
ally a circuit of low resistance) and for that reason, among 
others, is not as suitable for general therapeutical work as the 
Bichromate. However a battery of twenty to sixty cells ar- 
ranged in a cabinet is sometimes employed by physicians for 
office practice. [T. 173.—8. B. 37.] 
2. Electric Light Wires.—For the physician who 
thoroughly understands the principles of electricity there can 
be no more convenient and powerful source of electrical energy 
than that furnished in our larger cities by the cables of the 
Incandescent System of Electric Lighting. This source of 
electricity is especially suited to the electro-cautery being for 
this purpose far superior to the very best galvanic battery and 
vastly more convenient. 
A special piece of apparatus to reduce the current strength 
is, however, necessary, and one of the objects of this course 
will be the explanation of the method by which the incandes- 
cent current can be adapted to the physician’s use. Any 
attempt to use the electric light current by one who does not 
thoroughly understand what he is about is attended with great 
danger both to patient and operator. 
The current of the Arc System cannot be readily employed 
as a source of therapeutical electricity as it is too strong to be 
easily managed by any one who is not an electrical expert. 
3. Local’Action and Amalgamation.—All batter- 
ies whose fluids contain free acid must have their zincs amalga- 
mated on account of the “ local action ” which would otherwise 
quickly destroy them. It is not necessary to amalgamate the 
zincs of sal ammoniac batteries although such amalgamation is 
no detriment but rather an advantage. The same is true of any 
battery which does not contain a free acid. [T. 161, 162.—8. 
E. 25, 26.] 
To amalgamate a zinc thoroughly clean it in dilute sulphuric 4 
LOCAL ACTION AND AMALGAMATION. 
acid and then pour upon it a little mercury. Rub the latter 
over the entire surface of zinc exposed to the battery fluid. 
Another method is to place the zinc in a solution of a mercury 
salt containing a little free sulphuric acid. A zinc must be so 
thoroughly covered with mercury that it will not effervesce 
when left in dilute sulphuric acid. Some battery zincs are so 
impure that it is almost or quite impossible to amalgamate 
them enough. This is especially true when the zinc contains 
little pieces of graphitic carbon. Such zincs should be discarded 
and new ones obtained. 
Exp. 1. Take pieces of any two metals which happen to be at 
hand (tin, lead, copper, nails, silver coins, zinc, gold ring, nickel five 
cent pieces), immerse them in dilute sulphuric acid (or any other dilute 
acid, alkali or solution of a salt) and connect them by short pieces of 
copper wire including aG in the circuit. Test several pairs of metals 
and notice that you get different defiections with different metals. In 
dilute acids the greatest deflection will be obtained with zinc in combin- 
ation with some incorrodible metal like gold. Hence zinc is the metal 
which is almost universally used for the corrodible plate of batteries. 
[T. 72.—B. R. 24.f 
RXPEKIMENTS. 
Exp. 2. To prove that the current flows through the fluid as well 
as through the wire place a piece of zinc above and a piece of copper or 
silver below the tongue. Now connect them with a wire and notice the 
sharp metallic taste produced by the passage of the current through the 
tongue. In this Exp. the fluids of the mouth take the place of the 
dilute acid of the battery. By using different pairs of metals you can 
in this manner also easily detect the fact that the strength of the cur- 
rent varies with the metals employed, being greatest when one of the 
metals is zinc. Try it. Place a piece of zinc on the tongue and then 
bring it in contact with the gold or silver filling of your tooth. What 
do you notice? Explain the phenomenon. 
Exp. 3, Make a Voltaic Pile [T. 150— B. R. 80J with a dozen zinc and 
copper plates separated by pieces of paper wet in strong brine. Place 
your finger on the lower plate and your tongue on the upper one. Pass 
the current through your G (u. c.) including a resistance coil of 100 
ohms, and compare the deflection with that given by one or two Volta's 
cells through the same circuit. This Exp. illustrates the principle upon 
which electric belts, pads, etc., [B. R. 445] are constructed. The moisture 
of the body supplies the fluid, the belt itself containing, in some cases HOW TO SOLDEE. 
5 
at least, some hygroscopic salt which absorbs the moisture thus sup- 
plied. A well constructed belt will give a very fair current for a time, 
but it is liable to gradually fail on account of the corrosion of the 
plates and connections. 
Exp. 4. Dip a piece of unamalgamated zinc in dilute sulphuric acid 
and notice the evolution of hydrogen from its surface. Now immerse a 
piece of copper in the acid and bring the upper ends of the two metals 
in contact. Notice that the hydrogen now comes from the copper in- 
stead of the zinc plate. Is the copper being corroded? Is the zinc? 
Bring the plates in contact at the bottom instead of the top and notice 
that the effect is the same. Separate the plates from each other, connect 
them by a wire and observe that the effect is still the same even when 
the wire is a very long one. [T. 160.] Notice that in this Exp. the hy- 
drogen does not entirely cease to come from the zinc plate. Why? [T. 
161] 
Exp. 5. Bend a piece of zinc back and forth several times and 
notice that it is quite tough. Now amalgamate it and bend it again. 
Notice how brittle it has become and remember that amalgamated bat- 
tery zincs are very brittle and must be handled with care. 
Caution.—Remember that finger rings, watches, chains, etc., as well 
as battery zincs, may be amalgamated and perhaps injured thereby. 
Mercury may be largely driven off from any piece of jewelry by slightly 
heating it over a lamp or gas burner. Great care must be used in this 
process if the piece happens to contain a setting. 
Exp. 6. Eepeat Exp. 4, using a piece of amalgamated zinc instead 
of the unamalgamated. The results obtained are different in one par- 
ticular. What is it and why the difference ? 
Exp. 7. E,ead#he next paragraph upon soldering and then make a 
Volta's cell like the model on side table. Amalgamate the zinc after 
everything else is done. 
4. How to Solder.—It is quite desirable that one who 
handles electrical apparatus to any extent should know how to 
solder. The following suggestions are accordingly given: 
1. Have the soldering iron hot enough to melt the solder 
about as readily as a warm knife blade melts butter. Do not 
let it get red hot as the “ tinning ” will be thereby burned off. 
2. The parts to be united must be scraped clean with a 
knife or a piece of sandpaper. 
3. A “ soldering fluid ”or flux must always be used. Eosin 6 
RULES AND MEMORANDA. 
is used for soldering tin or lead; zinc chloride (made by add- 
ing an excess of zinc to dilute muriatic acid) for soldering cop- 
per, brass, zinc, nickel, German silver, silver and gold; for 
soldering iron use zinc chloride solution to which some sal- 
ammoniac has been added. 
4. Small pieces of metal and wires may be soldered without 
the use of a soldering iron by clamping or twisting them to- 
gether, laying a small piece of solder upon the joint, adding a 
drop of soldering fluid and heating over an alcohol lamp or gas 
burner. The melted solder will spread between the pieces by 
capillary action. 
5. Rules and Memoranda.—The following rules for 
the use and care of batteries should be firmly fixed in the 
memory: 
1. Dilute sulphuric, acid for batteries is made by adding, 
with constant stirring, one volume of the commercial acid to 
fifteen volumes of cold water in a vessel not easily broken by 
heat. Never add the water to the acid. Why? 
2. To make Bichromate Fluid add one volume of commer- 
cial sulphuric acid to twenty volumes of cold water, stirring 
constantly. Then saturate the solution with bichromate of 
potash. About four ounces of bichromate is required to sat- 
urate a quart of the dilute acid. 
The following formula requires a little more work but fur- 
nishes a rather better fluid, especially for a cautery battery: To 
one pound of finely powdered bichromate of potash, in a por- 
celain dish, add with constant stirring two pounds of strong 
sulphuric acid. To this mixture add carefully and with con- 
stant stirring twelve pounds of cold water. When cold [B. B. 
35] the solution is ready to use. It is convenient to remember 
that a pint of water weighs about one pound and a pint of sul- 
phuric acid about one and three-fourths pounds. 
It is a good plan to add about one ounce of a soluble mer- 
cury salt to the quart of Bichromate Fluid which is to be used 
in a battery having carbon plates. This will keep the zincs 
well amalgamated. Fluid containing mercury salts should not RULES AND MEMORANDA. 
7 
be used in cells employing platinum plates as the action of the 
battery is liable to amalgamate the platinum. 
Chromic acid (chromium trioxide) may be used in place of 
bichromate of potash in the proportion of three parts of chro- 
mic acid for every four parts ot bichromate. It is preferable to 
bichromate—especially for cautery batteries. 
3. Bichromate fluid is no longer good after it has become 
green. Why? 
4. Battery cells should never be filled so full that the fluid 
comes in contact with the metal straps or connectors attached 
to the upper ends of the battery plates. 
5. In batteries employing porous cups the fluid about the in- 
corrodible plate should never be higher (nor, in fact, quite as 
high) as the fluid about the zincs. By observing this rule the 
diffusion of the oxidizing fluid towards the zinc is delayed. 
6. No effervescence should occur in a battery cell which is 
working properly. It indicates local action and, consequently, 
incomplete amalgamation. Battery zincs must be occasionally 
re-amalgamated. 
7. After being used, all batteries (excepting the sal-ammo- 
niac and a few7 others which are intended to be left set up) should 
have their plates taken out of the fluids immediately, and in 
case of the two fluid batteries the fluids should be put into 
their respective bottles for preservation and not allowed to 
stand in the battery cells. Porous jars must be soaked in 
water for several days to remove from their pores the salts 
which, otherwise, are liable to crystallize and break the jars. 
See specimens of jars thus broken on the side table. 
8. The carbon clamps and connections of Bunsen’s bat- 
tery should never be left clamped to the carbons as the acid 
gradually creeps up and corrodes them. 
9. The evolution by Bunsen’s battery of the disagreeable 
and poisonous fumes of nitric oxide may be largely prevented 
by adding to the nitric acid a little bichromate of potash. 8 
THE GALVANOMETER. 
6. The Galvanometer.—No one can successfully use 
electricity without understanding the principles of and at times 
using some form of galvanometer. Even a very simple and 
cheap instrument may be made, in the hands of a skilled oper- 
ator, to yield valuable and comparatively accurate results. A 
galvanometer adapted to the currents employed in electro-ther- 
apeutics is called a “ milliamperemeter; ” and one adapted to the 
heavy currents used in electric lighting is often called an 
“ ammeter ” or an “ amperemeter.” A galvanometer may be 
used, 
1. To determine whether or not any current is flowing. 
2. To determine the direction of the current. 
3. To measure the strength of the current. 
4. To measure the resistance of a circuit. 
The great fundamental phenomenon of electricity upon which 
the construction of the galvanometer depends is the following: 
A freely suspended magnetic needle always tends to place it- 
self at right angles to a wire through which a current is flowing. 
[T. 185, 186, 187, 188, 189, 197, 198, 199.—8. R. 40.] 
The galvanometer which you will use in the laboratory is a 
tangent galvanometer in which the needle is suspended above 
the coil of wire instead of within it. The instrument contains 
two coils, the lower one for very strong and the upper one for 
weak currents. 
For deflections not greater than 10° or 15° the current is 
nearly proportioned to the deflection. [T. 198, 199.] In using 
these particular instruments the following table will be of con- 
siderable assistance. The table gives approximately the 
strength of the current in milliamperes for deflections, pro- 
duced by the upper coil, not exceeding 24°. This table applies 
only to these particular galvanometers. In general every gal- 
vanometer must be calibrated by itself and its own table con- 
structed from actual experiment. [T. 198.] RULES FOR THE GALVANOMETER. 
9 
Giving the Current in Milliamperes, Corresponding to Various Defec- 
tions of the Galvanometer. 
Table 
1° 
1.8 
9° 
17.0 
17° 
35.0 
2° 
3.6 
10° 
19.0 
18° 
38.0 
3" 
5.4 
11° 
21.2 
19° 
41.5 
4° 
7.0 
12° 
23.4 
20° 
45.0 
5° 
9.0 
13° 
25.6 
21° 
49.0 
6° 
11.0 
14= 
27.8 
22° 
54.0 
7° 
13.0 
15° 
30.0 
23° 
60.0 
8“ 
15.0 
16° 
32.5 
24° 
67.0 
By thoroughly mastering the principles of the galvanometer a 
physician can easily construct one for himself (out of a good 
pocket compass and a few feet of insulated copper wire) which 
will serve all practical purposes in electro-therapeutics. In 
order to measure the current the instrument must be calibrated 
and a table like the above constructed. This can be easily done 
if one has a few resistance coils and knows how to apply Ohm’s 
Law. 
7. Rules for Usingr the Galvanometer.—The fol- 
lowing precautions must be observed in using these galvanome- 
ters. Similar rules apply to all other instruments of like con- 
struction. 
1. The galvanometer must be so placed on the table that 
the coil shall be parallel to the needle when no current is flow- 
ing. 
2. On account of the danger of injuring the instrument (by 
fusing the wire or burning the insulation) no current should be 
sent through it which gives a greater deflection than 85°; nor 
should any current be allowed to flow longer than is necessary 
to take the reading. 
3. Conducting wires must not be allowed to pass over or 
near the needle; and all resistance coils, magnets, pocket knives, 
pieces of iron, gas pipes, etc., must be kept at least two feet 
from the galvanometer. 
4. The most accurate results are obtained when the deflec- 
tions do not exceed 30° or 40°. Consequently use the upper or 10 
RULES FOR THE GALVANOMETER. 
lower coil according as the one or the other gives the most 
favorable deflection. 
EXPERIMENTS. 
Exp. 8. Magnetize a common sewing needle by rubbing it in one 
direction only with a horseshoe magnet. [T. 92—B. R. 6.] Then float the 
needle on a glass of water using a small piece of cork as a float. You 
now have a compass. [T. 88.] After the needle has come to rest in the 
magnetic meridian stretch a piece of copper wire above and parallel to 
it. No effect is noticed until a current be sent through the wire. What 
happens when a current from your Yolta’s cell is allowed to flow ? This 
is Oerstedt’s fundamental experiment. [T. 185.] 
Exp. 9. Modify this Exp. Bby using your G, which place on the 
table with its length pointing east and west. Now stretch the wire just 
above the needle and parallel to it. Notice carefully the effect; now 
place the wire below the needle and notice a slight difference in the 
result. What and why the difference? Wind the wire several times 
around the instrument and observe the marked increase in the deflection 
[T. 187,189.] 
Exp. 10. Modify the experiment in one other way. Notice how 
much deflection you get when only one strand of wire is held just above 
the needle. Now wind the wire into a coil of six or eight strands hav- 
ing a diameter of about two inches. Hold this coil (in a vertical posi- 
tion) just above and parallel to the needle and observe the deflection again. 
Why is it greater? This Exp. illustrates the construction of your gal- 
vanometer, in which, however, the coil is underneath instead of above 
the needle. 
Exp. 11. Place your G on the table with its Nto the west. Now 
pass the current of your Yolta’s cell. Why does not the needle move? 
This shows the necessity of observing the first rule under paragraph 7. 
Exp. 12. A galvanometer may be used to determine which is the + 
pole of a battery or any other current generator. In other words it will 
indicate the direction in which a current is flowing. Connect your Yol- 
ta’s cell to the G and notice in which direction the needle turns (in the 
same direction as the hands of a watch or the opposite). Now reverse 
the connections and notice that the needle swings in the opposite direc- 
tion. After having once determined in which direction the needle turns 
when one of its binding posts (distinguished from the other post by some 
sort of mark) is connected with the + pole of a battery whose polarity 
is known it is evident that the instrument can thereafter be used to dis- 
tinguish between the poles of a battery which is out of sight (in a 11 
BATTERY POLARIZATION. 
cabinet or in the cellar for example) or to determine the polarity of the 
current derived from an electric light circuit. This is of importance 
because in surgical electrolysis different effects are produced at the dif- 
ferent poles. 
Let a student on the opposite side of the table pass the wires from 
his battery through a crack or over the top of the desk while you deter- 
mine which is the + and which the pole. 
Take your G to the special piece of apparatus marked “ Generator 
A,” and determine the polarity of the wires which come from a battery 
in another part of the building. 
Exp. 13. Pass the current of one bichromate cell through your G 
(1. c.) and notice the deflection. Then without breaking the connections 
bend one of the conducting wires over and near to the needle. Notice 
that you get a different deflection showing the necessity of the third 
precaution, under paragraph 7. Bring a piece of iron, a coil carrying a 
current, a magnet, etc., near the needle and notice how they may change 
the true reading. 
8. Battery Polarization.—Almost every known form 
of battery gives its maximum current immediately after the cir- 
cuit is closed. A gradual decrease in the strength of the current 
is then observed with most batteries. This is called the “polar- 
ization of the battery,” and, in most cases, results from both a 
decrease of the electromotive force and a slight increase of the 
battery resistance. In Volta’s cell it occurs so quickly after the 
circuit is closed as to make its observation a matter of some 
difficulty while in the bichromate cell it may appear only after 
the lapse of several seconds or minutes. The cause of polar- 
ization is : (1) The deposition of a film of hydrogen gas upon 
the incorrodible plate; or, (2) The exhaustion in those batteries 
which do not evolve free hydrogen, of the thin layer of oxidiz- 
ing fluid which is in immediate contact with the incorrodible 
plate. [T. 163, 164.—8. E. 30, 31.] 
9. Prevention of Polarization.—Polarization due 
to a deposit of a film of hydrogen may be prevented: 
First, by some mechanical device for brushing off the film 
as fast as it forms. This is not a satisfactory method as it does 
not completely prevent the difficulty. 
Second, by using an oxidizing fluid about the incorrodible 12 
PREVENTION OF POLARIZATION. 
plate to burn up the hydrogen as fast as it forms. This is the 
most common method and effects a nearly complete prevention 
of polarization. 
Third, by using a solution of some suitable metallic salt 
about the incorrodible plate. Copper sulphate is generally 
used. In this case metallic copper instead of hydrogen is liber- 
ated and no polarization whatsoever occurs. [T. 165. ] 
Polarization due to exhaustion of the oxidizing fluid about 
the positive plate cannot be entirely avoided. It is not appre- 
ciable when a battery is upon a high resistance circuit, but be- 
comes quite troublesome upon a very low resistance which we 
always have with the galvano-cautery. It may be largely re- 
duced by agitating the fluids of the battery so as to renew the film 
of fluid next to the plate more rapidly than by its simple diffu- 
sion and cautery batteries are generally made so that the plates 
can be rocked back and forth when the battery is in use. A 
battery quickly recovers from this kind of polarization by 
simply being allowed to stand on open circuit for a few minutes. 
EXPERIMENTS, 
Exp. 14. Connect your G with the sal-ammoniac battery on the 
side table and notice that in a few moments the deflection begins to 
grow less. This is due to “ battery polarization.” Allow the cell to stand 
on open circuit for ten minutes and again test it. Observe that it has 
nearly or quite regained its former strength. For what purpose are these 
batteries especially suited ? 
Exp. 15. Test a gravity cell for polarization. Notice that you may 
leave the current on almost indefinitely without any sign of decrease in 
its strength. No battery is freer from polarization than a well con- 
structed and properly charged copper sulphate cell. Why, then, is not 
this cell used in practical electro-therapeutics ? 
Exp. 16. Make use of “ Apparatus B.” Read the directions attached 
thereto carefully and follow them exactly. Convince yourself of the 
following facts: 
1. A bichromate battery polarizes considerably upon a circuit of 
low resistance. 
2. This polarization is lessened by rocking the cell or by otherwise 
agitating the fluid so as to renew the oxidizing solution in immediate 
contact with the positive plate more rapidly than by simple diffusion. STRENGTH OF A CURRENT. 
13 
3. Upon a circuit of very high resistance the bichromate battery 
shows no marked polarization. 
10. What Determines the Strength of a Cur- 
rent : Ohm’s Law.—In order to have a clear understanding 
of the conditions upon which the strength of the current, in any 
particular case, depends we must sharply distinguish between 
the three following electrical quantities; 
1. The Current (C). Its unit of measurement is called 
Ampere. 
2. Electro-motive Force (E). Its unit of measurement is 
called Yolt. 
3. Resistance (R or r). Its unit of measurement is called 
Ohm. 
In the case of every current of electricity all three of these 
quantities are involved and the experimental study of electricity 
has shown that if we by any means know the value of any two 
of these quantities we can find out the value of the other by a 
simple calculation. 
The formula which gives us the value of C when R and E 
are known is 
E 
(1) C = 
R + r 
in which C is the current in amperes, E is the electro-motive 
force in volts, R is the battery resistance and r is the resistance 
of the rest of the circuit. This formula simply means that the 
strength of the current depends upon two things only; (1), the 
force or electrical pressure which is driving the electricity 
round the circuit, and (2), the resistance or friction of the 
entire circuit. It further states that the strength of the cur- 
rent in amperes is equal to the number of volts electro-motive 
force divided by the number of ohms resistance which we hap- 
pen to have in any particular case. 
This statement is true in every case of a current flowing in 
closed circuit and constitutes a great Law of Electricity known 
the world over as Ohm’s Law in memory of the man who dis- 
covered it. [T. 155, 158, 179, 345. B. R. Chap. YI, p. 65. ] USEFUL MEMORANDA. 
This formula may be written in two other ways: 
(2) E=C (R+r) 
E 
(3) (R+r) = 
C 
The second formula gives us the value of E when we know 
the value of C and (R+r), while the third gives us the total 
resistance of a circuit when we know the values of E and C. 
11. Useful Memoranda, —ln applying the above 
formulae the following facts and constants should be borne in 
mind; 
depends almost entirely upon the nature of the plates and 
1. The Eof a cell is independent of its size or shape and 
fluids employed. 
Each kind of cell has its own particular E. The following 
table gives the E of several of the more important batteries. 
These values are for freshly charged cells and are consequently 
too large for cells whose fluids are partially exhausted. [T. 178. 
—B. R. 68.] 
Volta’s cell, 8 volt. 
Copper Sulphate cells, 1.0 “ 
Sal-ammoniac cells, 1.4 “ 
Sulphate of Mercury cells, 1.5 “ 
Bunsen cells, 1.8 “ 
Bichromate of Potash cell, 1.9 “ 
2. Every battery cell offers more or less resistance to the 
passage of the current. This may be looked upon as friction— 
electrical friction, and varies from one-tenth to five or six ohms 
according to the size and kind of cell, depth of fluid, distance 
between plates, concentration of the fluids, temperature, etc. 
In general the resistance of a one or two quart Bunsen or 
Bichromate cell may be taken to be one-third of an ohm. The 
resistance of a Gravity cell, like those upon the side table, is 
about three ohms, [T. 181— B. R. 75,] 
3. Every part of a circuit outside of the battery also has USEFUL MEMORANDA. 
15 
some resistance. In many cases this can be approximately 
known by remembering: 
1. The resistance of any piece of wire is given by the formula 
10 a I 
r 
dl 
in which d = the diameter of the wire in thousandths of an inch. 
I = the length of the wire in feet. 
“a” = a number which varies with the material out of which the 
wire is made. The following table gives the value of “a” for the vari- 
ous substances named: 
Copper, 1. 
Brass, 4. 
Iron, 6. 
Platinum, 6. 
German Silver, 14. 
Mercury, 60. 
Dilute Sulphuric Acid, acid, 2 000 000. 
Water, 40 000 000. 
Gutta Percha, 200 000 000 000 000 000 000. 
Shellac, 4 000 000 000 000 000 000 000. 
[T. 347]. 
2. The resistance of the body from hand to hand when cylindrical 
electrodes are firmly held in moist hands is about 4 000 ohms. 
3. The resistance of living tissue between two needle electrodes 
about one inch apart is approximately 500 ohms. 
4. There are three methods of coupling cells together: 
First. Series. This is effected by connecting the positive plate of 
one cell with the negative plate of the next and so on through the 
whole number. 
Second. Muliple Arc. This consists in connecting all the positive 
plates together to form one large multiple plate and all of the negative 
plates together to form one large multiple negative plate. 
Third. Partly in series and partly in muliple arc. This consists in 
forming a number of groups coupled in m. a. which grougs are after- 
wards coupled in series exactly as if each group were a large cell instead 
of a muliple cell. Of course the number of cell required for this 
method is equal to the product of the number in series multiplied by 
the number In m. a. 1 
5. The Eof a number of cells coupled in series [T. 350] is equal to 
the sum of the electromotive forces of the several cells. 16 
BEST METHOD OF COUPLING CELLS. 
6. The Eof a number of cells coupled in multiple arc is the same 
as that of one cell. [T. 350.] 
7. The Eof a battery composed of S cells in series and M cells in 
multiple arc (the total number of cells being S x M) is equal to S times 
the E of one cell. 
8. The Eof a number of cells coupled in series is equal to the sum 
of the resistances of the several cells. 
9. The Rof a number of cells coupled in the multiple arc is equal 
to the resistance of one cell divided by the number of cells thus coupled. 
10. The Rof a battery of S cells in series and M cells in multiple- 
s 
arc in equal to the resistance of one cell multiplied by 
M. 
just been stated there are three methods of coupling a number 
of cells together. 
12. The Best Method of Coupling Cells. As has 
First. All in series. 
Second. All in multiple arc. 
Third. Partly in series and partly in multiple arc. 
The question is often asked. “ which one of these methods is 
the best—which one will give the largest current?” 
Both theory and experience answers that no one of them is 
the best under all conditions. Sometimes one and sometimes 
another gives the maximum current depending upon the value of 
the external resistance. The one universal rule, which is a 
mathematical consequence of Ohm’s Law and of the facts just 
given respecting the E and E of batteries, is the following: 
That method of coupling which makes the battery resistance 
{IT) most nearly equal to the external resistance (r) will give 
in every case the maximum current of which the battery is cap- 
able [T. 351.] 
In accordance with this rule it follows that when the ex- 
ternal resistance is large, say above 15 ohms, a battery should 
be coupled in series; if r is very small, say not more than one 
twenty-fifth of an ohm, the battery should be in m. a.; while if 
r is in the neighborhood of one oiim some arrangement in both 
s. and m. a. will give the best results. BEST METHOD OF COUPLING CELLS. 
17 
Exp. 17. A closed circuit is necessary to the existence of a current 
and in such a circuit the strength of the current is the same at all points. 
EXPERIMENTS. 
Prove this proposition hy putting in circuit four cells and several 
resistance coils of 500 to 1000 ohms total resistance. Now introduce 
your G (u. c.) at various points in the circuit—between any two of the 
cells, or any two of the coils, between the coils and the battery, etc.— 
and notice that you get exactly the same deflection at all points. 
Exp. 18. The Eof a cell is independent of its size. Prove this by put- 
ting in circuit with your G a resistance of about 200 ohms and then, in 
turn, the small bichromate cell on side table, the bichromate cell on your 
own table, and finally the large cell which is on the side table. Notice 
that you get no increase in the deflection as the size increases. 
Exp. 19. The Eof a cell is independent of the depth of the fluid. 
Prove by passing the current from one of your cells through the G and 
a 200 ohm coil. Gradually lift the plates out of the fluid and notice that 
the deflection does not change until just before the plates leave the fluid 
entirely. 
Exp. 20. The Rof a cell increases as the immersed surface of the 
plates decreases. Hence the larger and fuller a cell is the less will be its 
resistance. 
Prove by sending through the lower coil of you G the current of one 
of your bichromate cells. Gradually raise the plates out of the fluid 
and observe the effect on the needle. Compare the currents given by 
the large and small cells on the side table and notice that the large cell 
gives the greatest current when connected with your G (1. c.) 
Exp. 21. Use two cells in series and send the current through your 
G (1. c.) Take the reading. Now introduce in succession the following 
resistance :1, 2, 5,10, 25 ohms. In each case calculate the current by 
Ohm’s Law and notice how the calculated currents agree in general 
with the deflections obtained. 
Exp. 22. Use the 1. c. of your Gto measure the currents given by 1, 
2, 3, 4 cells successively. Couple the cells in each case in series. Why 
do not the whole four cells give a greater current than one cell ? Ohm’s 
Law will explain it. Calculate the current in each case. The rof the 
G (1. c.) is practically zero. 
Exp. 23. Repeat Exp. 22, using the u. c, of your G and including a r 
of 100 to 200 ohms in the circuit. There is now a gradual increase in 
the current as the number of cells increases. Why ? Ohm’s Law will 
answer the question. 18 
ELECTRICAL MEASUREMENTS. 
Exp. 24. Again repeat Exp. 22 but in each case couple the cells in 
m. a. instead of s. You now get a greater C with four cells than with 
one. Why so in this case and not in Exp. 22 ? 
Exp. 25. Use your G (u. c.) and a r of about 200 ohms. Measure in 
succession the currents of 1, 2, 3, 4 cells coupled in m. a. The whole 
four cells give no greater current than does one cell. Why? Ohm’s 
Law will explain the mystery. Calculate the current in each case. The 
rof the G (u. c.) is about XV ohm. 
13. Electrical Measurements.—A few experiments 
to illustrate the manner in which valuable approximate electri- 
cal measurements can be readily made with very simple appa- 
ratus will now be given. 
Exp. 26. To measure E without using a galvanometer.— Electro- 
motive forces not exceeding about 8 volts can be easily measured with 
approximate accuracy by means of the tongue. Place the wires from 
various galvanic cells (the list given on page 14 will serve admirably) 
upon your tongue and notice the difference in the sharpness of the sen- 
sation. After a little practice this method of tasting the E will enable 
you to measure electromotive forces with tolerable accuracy and will 
furnish the readiest means of determining whether a battery is giving 
its due E. 
EXPERIMENTS. 
Use the gravity battery and practice the determination of E as fol- 
lows: Let one student turn his back to the battery and place the wires 
upon his tongue while another student shifts one of the wires at the 
battery so as to throw in circuit from Ito 6 cells. A little practice will 
enable you to tell by taste the number of cells thrown in, and will give 
you an idea of the taste of from 1 to 6 volts. 
By comparing the E to be measured with that of a standard battery 
like the gravity, this method can be made quite accurate. 
Exp. 27. To measure Eby means of the galvanometer.—Measure the 
Eof three different cells as follows; Send the current of one gravity 
cell through your G (u. c.) and a r of 100 ohms. Now take the reading 
given by the cell whose E you wish to measure and call it B, Since in 
both cases the resistance is almost exactly the same, it follows from 
Ohm’s Law that the deflections in the two cases are proportioned to the 
electromotive forces. Consequently if we let the force which we are 
measuring be represented by x the following proportion will give us 
its value: 
1 : x :: A : B 
B 
and x = volts. 
A ELECTRICAL MEASUREMENST. 
19 
For quite high electromotive forces, say 5 to 25 volts, it will be nec- 
essary to use several gravity (or other standard) cells and such a resist- 
ance as will make the deflection about 10°. The number of cells used 
should be such as to give an E somewhere near that to be measured. 
Exp. 28. To measure R by using resistance coils.—Put in cir- 
cuit the resistance to be measured, your G (u. c.) and enough battery to 
give from 10° to 10° deflection. Take the reading. Now take out the 
unknown r and put in its place some of the r coils which are upon the 
side table. Try various coils and combinations of coils until you get the 
same deflection as before. When you have done this the total rof the 
coils is equal to the r which you are measuring. 
By this method measure the r of coils “ P” and “W” on side table. 
Exp. 29, To measure R without resistance coils.—This requires 
a calibrated galvanometer. Your G (u. c.) has been calibrated and the 
table on page 9 give the current corresponding to various deflections. 
Put in circuit the r to be determined, your G (u. c.) and enough bat- 
tery to give 5° to 15° deflection. From the table take the value of C 
(in amperes-—not milliamperes) corresponding to the deflection obtained. 
You know the value of E. Now substitute these values in the third 
E 
form of Ohm’s Law, (R -j- r) = —, and you will have the total resistance 
C 
of the circuit. Substract R from this and you have left the resistance 
whose value you were seeking. 
The accuracy of this method of measuring resistance depends upon 
the accuracy with which the G is calibrated and the precission with 
which you know the values of E and R. In generaHhis method is more 
accurate for high than for low resistance, but it is always less reliable 
than the other method. 
Measure the resistances of coils “P” and “W” and notice how the 
results agree with those obtained in Exp. 28. 
Exp. 30. Measure the resistance of the body from hand to hand by 
the second method. Also the resistance of the hand from palm to back. 
In making these measurements the connection with the hand must be 
made by means of large copper plates or cylinders covered with paper 
or cloth wet with salt solution and firmly pressed upon the hand. 
Exp. 31. Try to make the measurement of Exp. 30. by using dry 
wires or plates of copper pressed upon the dry skin. The resistance is 
now so great that you may be unable to get any appreciable deflection 
even with a large number of cells. This illustrates the necessity of 
using electrodes covered with wet sponge, cloth or buckskin when using 
electricity upon a patient. There is also another reason for using 20 
DIVIDED CURRENTS. 
covered electrodes which we shall notice when we take up the subject 
of electrolysis. 
14, Divided Currents.—If the poles of a battery be 
connected by two or more separate wires the current will always 
divide and each wire will carry a certain definite proportion of 
it. The two principal laws of divided currents are the following: 
1. The sum of the currents in the several branches is 
equal to the main current. 
2. Each branch carries such a proportion of the whole 
current as its conductivity bears to the sum of the conductivi- 
ties of all the branches. 
The conductivity of a conductor is the reciprocal of its resis- 
1 
tance, i. e., conductivity = . The conductivity of a 
resistance. 
number of strands, side by side, is equal to the sum of the 
conductivities of the several strands. 
To find the net resistance of such a multiple-branch conduc- 
tor add together the conductivities of the several branches and 
then take the reciprocal of this sum. [T. 353, 346.] 
15. Shunts.—When any two points of a circuit are con- 
nected by a wire some of the current will be deflected from the 
main circuit and will pass through the wire. Such a wire is 
called a “shunt.” A shunt is evidently one branch of a divided 
circuit and the laws governing the amount of current which it 
will deflect from the main circuit are evidently the same as 
those just given for divided currents. 
The subject of divided currents is of importance as it shows 
us that we cannot confine the current to a single nerve or muscle 
when using electricity upon the human body. When, for ex- 
ample, one electrode is placed upon the back and the other upon 
the epigastrium the current will not be confined to the path 
traced by a straight line connecting the two points, but will 
spread out and traverse all parts of the trunk, the strength of 
the current, however, being less and less as the part is more and 
more remote from the straight line joining the electrodes. [B. B. 
Chap. X, p. 168] ELECTRIC LIGHT CURRENT. 
21 
EXPERIMENTS. 
Exp. 32. Put in circuit your G (u. c.), ar of about 10 ohms and one 
cell of battery. Take the reading. Now without interrupting the cur- 
rent join the two poles of the battery by several feet of rather fine 
wire. Notice how the deflection drops but does not become zero. The 
wire is a “shunt” and is taking the principal part of the current. Now 
use a short, heavy wire and notice that the needle drops still more, or 
possibly remains at zero, showing that the less the resistance of the 
shunt the more of the current will it take. 
Exp. 33. Connect the poles of your battery by two circuits one of 
which contains about 10 or 15 ohms and the other about 100 or 200 ohms 
res. Now introduce your G (u. c.) first in one circuit arid then in the 
other and observe the deflections. Notice that the currents are inversely 
proportional to the resistances of the two circuits; or in other words the 
currents are proportional to the conductivities of the two branches. 
Exp. 34. Wet the back of your head with a little salt solution and 
then apply one electrode to the spot and the other to the forehead using 
a battery of 4 cells. Do this carefully making the contact with the 
back of the head last and slowly by first pressing the electrode very 
lightly on the hair and then more firmly. If you become dizzy 
stop the Exp. There is no danger if you follow directions carefully. 
Notice that you get a metallic taste in the mouth showing that some of 
the current is deflected as low as the tongue. A current sent through 
the body from epigastrium to the back has been known to cause this 
metallic taste although the amount of current that reached the nerve 
of taste must have been almost infinitesimal. 
16. How to Use the Electric Light Current.—lt 
is by taking advantage of this property of the shunt to deflect a 
part of the current that we can adapt the electric light current 
to electro-therapeutics. As before stated a special piece of 
apparatus is necessary. This apparatus is in reality a shunt of 
peculiar construction, and the following diagram illustrates the 
method of using it: 
M N represents a box containing a number of resistance 
coils having the values indicated by the numbers under each. 
These coils are connected with the binding posts on the top of 
the instrument as shown in the cut. The electric light cables 
are connected by leading wires to the horizontal portions of the 
end posts A and B. The electrode wires are then connected 22 
ELECTRIC LIGHT CURRENT. 
with any two of the posts—those two being selected which give 
the required electromotive force. What the E between any two 
posts is may be readily ascertained. The E between the two 
light cables is always about 100 volts. The E between the end 
binding posts is consequently 100 volts and that between any 
two posts taken at random is such a proportion of 100 volts as 
the resistance between those posts is to the total resistance of 
the instrument. For example, if the electrodes are attached to 
posts 4 and 6, the included resistance is 100 + 50 = 150 ohms; 
the total resistance of the box is 1000 ohms; the E between 4 
and 6 is consequently tVoo of 100 volts, or 15 volts. Since in 
this expression (rVo°o~ X 100) the numerator is the only number 
which is changed in changing the electrodes from one set of 
posts to another we may write the expression for the E between 
any two posts thus: 
B 
E = X 100 or 
1000 
1 
E= B 
10 
in which B represents the resistance between the two posts em- 
ployed. In other words the E at the electrodes which are 
attached to the instrument is in every case numerically equal 
to -A of the resistance included between the posts used. 
These statements presuppose that the current is being sent ELECTROLYSIS. 
23 
through living tissue which always offers a high resistance. If 
the current be employed on a low resistance the above state- 
ments must be somewhat modified; but in a general way they 
remain true and in any case the actual E could be calculated 
by means of Ohm’s Law and the laws for divided currents 
already given. 
17. Electrolysis.—(l) Every liquid compound or solu- 
tion which is capable of conducting the current is called an 
electrolyte. Some liquids like bromine, kerosene and other 
oils generally, turpentine, etc., do not act as conductors and are 
not called electrolytes, nor are elements in the liquid state (e.g. 
melted lead, mercury, etc.,) called electrolytes. 
(2) An electrolyte is always decomposed by the current 
which passes through it into at least two products, called ions, 
which are invariably liberated in immediate contact with the 
surface of the electrodes. The ion collecting at the + electrode 
(anode) is called the anion; that collecting at the electrode 
(kathode) is called the kathion.. 
(3) The quantity of electrolyte decomposed is directly 
proportional to the quantity of electricity which is sent 
through it. 
A current of one ampere will decompose a grain of water 
(equal to a large drop) in twelve minutes. 
A one ampere current will deposit from a solution of copper 
sulphate A of a grain of copper per minute. 
(4) In most cases the ions are elements (or groups of ele- 
ments) in the “nascent state”—i. e., a state of unusual chemi- 
cal activity. In consequence of this fact it frequently happens 
that an ion, instead of being evolved as a free ion, combines 
chemically with the material constituting the electrode or with 
the electrolyte itself. 
(5) It thus happens in many cases that the product actually 
appearing at the electrodes is not the original ion but a secon- 
dary product due to the chemical action of the true ion upon 
the electrode or upon the electrolyte. What the ions are in any 
Particular case and whether or not secondary products are 24 
CORROSION OF THE ELECTRODES. 
formed must in every case be learned by reference to a standard 
work on chemistry or electricity. 
In general it may be stated that in the electrolysis of salts 
of the alkalies free caustic alkali and hydrogen appear at the 
kathode while free acid and oxygen appear at the anode. Salts 
of the heavy metals usually give a deposit of that metal at the 
kathode and free acid and oxygen at the anode. [Read care- 
fully T. 205 to 214.—8. R. Chap. IV, p. 45.] 
18. Corrosion of the Electrodes*—Since acid radi- 
cles and the chemico-negative elements like chlorine, bromine, 
iodine, etc., are liberated at the anode and that too in the nas- 
cent state we would naturally expect to find the anode corroded 
by the process of electrolysis. Experience bears out the expec- 
tation, and only by employing some substance like gold, plati- 
num or carbon can we avoid forming a solution of the -f elec- 
trode. Even these substances (excepting the carbon) are cor- 
roded if the electrolyte contains a chloride. As a general thing 
the kathode is not corroded. 
19. Surgical Electrolysis.—ln surgical electrolysis 
the electrodes in the shape of common steel needles (or better 
the three-sided harness maker’s needles) are thrust into the tis- 
sues which we wish to destroy, and the current allowed to flow 
for from one to ten minutes according to the necessity of the 
case. As might be anticipated from a knowledge of the general 
principles of electrolysis strongly alkaline products and some 
free hydrogen accumulate around the kathode while about the 
anode strongly acid products, a greater or less amount of dis- 
solved electrode, and (if the current be a very strong one) some 
oxygen make their appearance. The gases usually escape 
through the opening made by the needle while the other pro- 
ducts gradually diffuse away from the needles against which 
they are liberated, and in time impart their own acid or alkaline 
reaction to the tissues in the immediate vicinity of their respec- 
tive electrodes. 
Since all tissues of the body contain some chlorine in the 
form of chlorides a corrosion of the anode always occurs in sur- POLARIZATION OF ELECTRODES. 
25 
gical electrolysis. The attempt to prevent it by using gilded 
or platinized needles is vain. Some corrosion will occur with 
any metal that can be used, and although the corrosion is less 
with platinum needles, it is doubtful whether this advantage 
offsets the difference in cost and convenience. 
electrolysis together with the electrodes constitute a kind of bat- 
tery having in every case of surgical electrolysis an E of about 
lij volts. This is in consequence of a tendency upon the part 
of the ions to recombine and reform the original electrolyte— 
which, indeed, in some cases they will actually do if the proper 
conditions be fulfilled. The E thus evoked in electrolysis is 
called the “polarization of the electrodes” and tends to send a 
current around the circuit in the opposite direction to that of 
the original electrolyzing current, and unless the latter has an 
E greater than volts polarization will actually bring it to a 
stand still and thus prevent further electrolysis. 
20. Polarization of Electrodes.—The products of 
It follows as a practical consequence that in surgical elec- 
trolysis an E of more than 1| volts must be used in order to get 
any decomposition of the tissue fluids. In practice it is found 
that from 8 to 40 volts must be employed to secure satisfactory 
results. In applying Ohm’s Law to the calculation of the cur- 
rent in electrolysis it is, of course, necessary to subtract volts 
from the battery E in order to get the force which is effective 
in driving the current. [T. 413.] 
EXPERIMENTS. 
Caution.—Li performing the following experiments perfect clean- 
liness is absolutely necessary to success. Slight traces of acid upon the 
Ungers or the table may entirely reverse the results of an experiment. 
Exp. 35. Attach your platinum electrodes to the poles of 4 cells 
in series, including your G (u. c.) in the circuit. Now immerse the elec- 
trodes (only the platinum part) in a beaker of distilled water. Pure 
water is a non-conductor, but you will obtain some decomposition prob- 
ably, as even the distilled water of the laboratory is not absolutely 
pure. 
It ought, however, to be quite small in amount. Now add sulphuric 
acid to the beaker, one drop at a time, stirring after each addition. 26 
EXPERIMENTS. 
Notice the marked increase in the current as indicated both by the G 
and the increased volume of gases evolved. 
Exp. 36. Repeat Exp. 35 using a strong solution of common salt 
instead of sulphuric acid. This Exp. illustrates the advantage of wet- 
ting sponge electrodes with a salt solution instead of pure water. 
Exp. 37. Electrolyse a solution of copper sulphate using platinum 
electrodes and a battery of two cells. Observe the deposit of copper 
on the kathode. This illustrates the principle upon which electro-plat- 
ing depends. You have electro-plated the electrode. If a solution of 
silver or gold had been used you would have obtained a deposit of these 
metals instead of copper. Remember that in electrolysis hydrogen and 
the metals always go to the kathode. Electrolysis, then, furnishes a 
ready method of distinguishing the poles of battery which is out of 
sight or the polarity of electric light wires. 
Dissolve the copper off from the electrode by immersing it (only the 
platinum part) in the beaker of nitric acid on the side table. 
Exp. 38 Determine the polarity of “Generator D”by means of 
electrolysis. 
Exp. 39. Electrolyze a solution of copper sulphate; (1) with plati- 
num electrodes; (2) with copper electrodes. In each case have your 
G (u. c.) in circuit and take the readings carefully. The copper elec- 
trodes must be of the same size as the platinum and held at the same 
distance apart. Notice that you get a stronger current with the copper 
than with the platinum electrodes. Why? Is the copper anode dis- 
solved ? 
This illustrates the principle upon which the so-called non-polariz- 
nble electrodes are constructed. The anion is allowed to combine with 
the same kind of metal that is being deposited at the kathode and there 
Is consequently no permanent decomposition of the salt. [T. 231. 
B. R. 327.] 
Exp. 40. To prove that copper is dissolved at the anode in the pre- 
ceding Exp. use a slightly tarnished piece of copper for that electrode, 
and notice that it becomes clean and bright in consequence of the super- 
ficial corrosion which takes place. 
Exp. 41. Electrolyze a solution of sodium sulphate, using four cells 
and platinum electrodes. The only apparent result is the evolution of 
hydrogen and oxygen. Is there any decomposition of the salt? Is the 
hydrogen a primary or secondary product? How about the oxygen? 
What has become of the sodium if the sodium sulphate has been decom- 
posed ? EXPERIMENTS. 
27 
Exp. 42. To prove the formation of free acid at the anode and of 
free alkali at the kathode in Exp. 41, add half an ounce of litmus solu- 
tion to the electrolyte and hold the electrodes very still and as far apart 
as possible for a few moments. Notice that hydrogen and oxygen are 
evolved as before, but that in addition the solution turns blue about the 
kathode and red about the anode. Do you understand why ? Be sure 
that you get a clear idea of what is going on in this Exp. 
Exp. 43. Make sure that your hand is perfectly clean and free from 
acid. Layja piece of blue litmus paper upon the palm and a piece of red 
litmus upon the back; wet both pieces with a neutral solution of sodium 
sulphate. Now press a clean copper anode upon the blue and a clean 
kathode upon the red paper and allow the current from four cells to 
flow for three or four minutes. Notice that the papers have changed 
color. Explain why. 
Exp. 44. Repeat Exp. 43, but in this case cover the electrodes with 
six or eight thicknesses of clean paper or cloth wet in sodium sulphate 
solution. Now the litmus paper will not change color. Why not? 
Prove that the acid and alkali in this case are liberated underneath 
the cloth or paper and in immediate contact with the copper by putting 
some pieces of litmus paper between the bare copper and its cloth cover- 
ing. This Exp. illustrates the value of covered electrodes in a second 
particular (see Exp. 31 for the other point), and from it we may deduce 
the following practical rule: 
A Rule Respecting Electrodes.— When using the galvanic cur- 
rent never place hare metallic electrodes in contact with the skin or a 
Mucous membrane unless you wish to obtain at the point of contact the 
caustic effects of free acid or alkali. 
Exp. 45. Remember that in all cases in which the current traverses 
a fluid, a wet cloth, sponge or paper, or the tissues of the body, it has a 
large resistance to overcome. 
It is consequently of great importance that we make this resistance 
as low as possible by using large electrodes, thoroughly wet with a salt 
solution, and firmly held in position whenever we desire to obtain a 
strong current. 
Fix these facts firmly in mind by measuring the current given by a 
battery of four cells under the following conditions; 
(1) Use bare copper wires as electrodes, pressing them firmly upon 
opposite sides of the dry hand. You will probably get no appreciable 
current. 
(2) Replace the wires with copper plates.-.Perhaps you now get a 
slig-ht deflection. 28 
EXPERIMENTS. 
(3) Wet the hand and hold the plates very lightly in place. A much 
stronger current now flows as your G indicates. 
(4) Finally press the plates Urmly upon the wet hand and observe 
the marked increase in the current. 
Exp. 46. Electrolyze a solution of common salt with carbon elec* 
trodes. Notice that you get the odor of free chlorine. Now use iron 
wire electrodes and observe that there is less chlorine evolved (perhaps 
none) but that the anode is corroded, giving a light colored solution of 
iron close to the electrode. In a little while the alkali liberated at the 
kathode will diffuse over and cause a precipitate of ferrous and ferric 
hydrates. 
A Caution. Iron salts are liable to cause a more or less permanent 
discoloration of the tissues in which they may he formed. In minor 
electro-surgical operations, then, such as the removal of hair, moles, warts, 
etc., the kathode rather than the anode should he employed. 
Exp. 47. Electrolyze a solution of sodium sulphate, using platinum 
electrodes and one Yolta’s cell. Put the G (u. c.) in circuit and have the 
electrodes in the fluid before closing the circuit. When all is ready keep 
your eye on the needle and close the circuit. Notice that the needle 
gives a start but quickly comes to rest again at the zero mark. Explain 
why. 
Now use a bichromate cell in place of Yolta’s and notice that now 
the needle remains slightly deflected after making the first jump. Ex- 
plain the cause of this difference in the two cases. 
Exp. 48. Polarized electrodes constitute a little independent battery 
which will send a current in the opposite direction to the polarizing cur- 
rent if permitted to do so by the removal of the primary battery. Prove 
this as follows : Put in circuit with your G (u. c.) four bichromate cells 
and a pair of large, clean copper electrodes between which is a thick pad 
of paper wet with a neutral solution of sodium sulphate. Allow the 
current to flow for four or five minutes and then quickly cut out the 
battery and bring together the wires which were in contact with the 
battery poles. This throws the G into circuit with the electrodes only. 
Observe that the needle swings in the opposite direction and then slowly 
falls back to the zero mark as the polarization gradually disappears. 
Exp. 49. Remove one or two hairs from the back of your hand by 
electrolysis, using a very fine sewing needle as the kathode. (B. R. 516.) 
A steel needle, if it be made the kathode as it should be, is just as good 
as the irido-platinum needle recommended by B. R. 
Exp. 50. In very many cases of electrolysis it is necessary to con- 
fine the action to a limited portion only of the tissues traversed by the GALVANO-CAUTERY. 
29 
needle, and especially is it desirable in many cases to avoid the forma- 
tion of any caustic products within the skin itself at the point of punc- 
ture. Needles which are insulated along a portion of their length must 
then be employed. Such needles can be purchased of dealers in electri- 
cal goods, but every physician can easily insulate his own needles and 
thus not only save considerable expense, but have just the right kind 
and size of needle for the operation in hand. 
Insulate a common darning needle as follows: Stick it into the end 
of a match or lead pencil and then dip it, eye downward, into a solution 
of shellac in alcohol (wood alcohol is cheaper and better than common 
alcohol for this purpose) made about as thick as glycerine. Immerse as 
far as you wish the insulation to extend—say to within a half inch of 
the point—and then dry out the alcohol above a lamp or gas burner. 
Towards the last heat it sufficiently to fuse the shellac which will 
spread over the needle and form a smooth, and almost glass-hard coating 
if the operation has been successfully done. It may be necessary to put 
on a second coating of shellac. It is absolutely necessary to drive of all 
the alcohol in order to obtain a coating so hard that it will not peal up 
when the needle is thrust through the skin. Great care must be taken 
not to burn the shellac. 
It is a good plan and much easier to insulate a variety of needles at 
a time by hanging them above a stove for several days or weeks. This 
will usually give a smoother coating, but it requires a long time for the 
shellac to dry sufficiently. 
21. Galvano-Cautery.—No other means of producing 
the actual cautery is comparable, in point of convenience and 
efficiency, with the electric current. In this application of elec- 
tricity to therapeutics the current is employed solely as a means 
of heating a piece of metal and does not to any appreciable 
extent enter the tissues which are operated upon. Our study 
of the Galvano-cautery then must be limited to the investiga- 
tion of those principles which relate to the development of heat 
by the electric current. 
Considerable difficulties beset this application of elec- 
tricity to medicine and “no one can expect to succeed with the 
galvano-cautery who is not to some degree a master of electro- 
physics.” 
The great fundamental facts upon which the construction of 
the galvano-cautery depends are the following: 30 
GALVANO-CAUTERY. 
1. Every conductor through which a current is flowing is 
heated thereby. 
2. The amount of heat developed in such a conductor 
(other conditions remaining constant) is proportional to its 
resistance. 
3. It is also proportional to the square of the strength of 
the current. 
4 The temperature to which a conductor will be heated 
depends upon 
(2) The rate at which it loses that heat by radiation, con- 
duction, etc. 
(1) The amount of heat developed within it. 
Ordinarily conducting wires, galvanometers and other in- 
struments do not carry sufficiently heavy currents for the warm- 
ing effects, which always exists to a greater or less degree, to 
become noticeable, but even these may become sensibly heated 
and even permanently injured by exceptionally strong currents. 
The following is a brief outline of the conditions which must 
be fulfilled in order to secure success with the electric cautery:— 
1. A very strong current is required, varying from three to 
fifty amperes, according to the size of the piece of metal to be 
heated. 
Since in all cases the resistance of the cautery itself is very 
low this condition is best fulfilled by using a battery of very 
low resistance. Conducting cords, connections, etc., must also 
be heavy so as to possess as little resistance as possible. 
2. This current must be under very complete control, so that 
its strength can be instantly modified to suit the changing re- 
sistance of the cautery. This may be done in one of two ways: 
(1) By raising or' lowering the plates in the fluid. This 
changes the battery resistance and consequently the strength 
of the current. 
(2) By including some form of rheostat in the circuit by 
which the resistance can be quickly and gradually increased 
or diminished, as the necessity of the case requires. This 
method is not so economical as (1) but it involves less danger 
of melting the cautery and give a more constant temperature. GALVANO-CAUTERY. 
31 
must be avoided as far as possible by rocking the plates or by 
using so large a brttery that it is not taxed to its utmost in fur- 
3. Changes in the strength of the current by polarization 
nishing the required current. This latter method of using an 
excess of battery power, cutting the current down to the re- 
quirements of the case by means of a rheostat as mentioned in* 
(2), is preferable to all other means of securing a constant 
current. 
The importance of having a current which is not continually 
varying in strength is apparent when we remember that the 
heat produced in the cautery varies as the square of the current. 
Slight changes, then, in current involve large changes in the 
temperature of the cautery. 
Instead of using a galvanic battery the Incandescent light 
current may be employed. A special piece of apparatus to 
reduce and regulate the current is necessary. A shunt similar 
to the one described on page 22 may be used; or, what is bet- 
ter, a direct resistance may be put in circuit with the cautery. 
Whichever method be used the apparatus must admit of rapid 
and gradual adjustment. It is not advisable for one who is not 
something of an expert to attempt the manufacture of such a 
piece of apparatus. It is probable that in the near future suit- 
able current regulators for medical purposes will be furnished 
by instrument dealers. 
[ln gaining a thorough understanding of the principle of the 
cautery a careful reading of the following references and a faith- 
ful carrying out of the experiments will be of great assistance. 
T. 366, 367, 369-B. R. Chap. 111, p. 673. Also pp. 78, 79, 80.' 
—Ganot’s Physics, 10th edition, pp. 734, 735, 736.] 
EXPERIMENTS. 
Exp. 51. To show the necessity of a strong current in producing 
the cautery connect the poles of two cells in m. a. by a fine copper wire 
about twelve inches long. Have your G. (1. c.) in circuit. Kotice to 
what extent the wire is warmed. ISTow slowly shorten the wire and ob- 
serve the increase in temperature as the current increases in strength. 
In this Exp. you are changing only the current strength by reducing 
the total rof the circuit. If shortened sufficiently the wire may become 
red hot and even melt. 32 
GALVANO-CAUTERY. 
Exp. 52. Connect the poles of two cells in m. a. by a foot of me- 
dium sized wire, having G. (1. c.) in circuit. Notice the temperature 
produced and the deflection. Now open circuit and file the wire nearly 
in two. Again close the circuit and observe the deflection. It will be 
nearly the same as before. Observe the temperature of the filed notch. 
Notice that it is much greater than that of the rest of the wire. This 
shows that the heat developed at any point increases with an increase 
in the resistance. This fact is often taken advantage of in searching for 
imperfect connections in a circuit. By placing one’s hand on the var- 
ious junctions the poor one can often be found by its feeling warmer 
than the rest. 
Exp. 53. The fact that the battery must have a low resistance is 
shown by connecting the poles of four cells in series by fifteen inches of 
medium sized wire, including the G (1. c.) in the circuit. Notice how 
warm the wire is and also the deflection. Now put the cells in m. a* 
and again make these observations. The wire is (perhaps) too hot to 
hold, and the G also indicates a much greater current. Calculate C in 
both cases by Ohm’s Law. 
Exp. 54, Show the necessity of low resistance battery by using (I) 
the small (2) the large cell on side table to drive the current through a 
few inches of copper wire. Use the Gin both cases and notice how 
much more effective the large cell is. 
Exp. 55. Twistjtogether three wires nine inches long and connect 
the poles of four cells in m. a. (G in circuit): 
Ist. With this twisted strand. 
2nd. With a single wire of same size as one strands and only 
three inches long. 
The resistance of the strand is just the same as that of the single 
wire and the current will be the same in both cases; but notice how 
much hotter the single wire becomes. Explain why. 
This illustrates the necessity of concentrating the resistance of the 
cautery in as small a piece of metal as possible, so as to avoid the cooling 
effect of a large exposed surface of metal. For this reason platinum is 
better than gold for a cautery as it has about six times the resistance of 
gold. The fact that it is less fusible is also important. 
Exp. 56. Close the poles of two cells in M. A. with a short piece of 
polished fine iron wire. Gradually shorten the wire until it becomes red 
hot. Then disconnect it and examine the surface. It has turned black 
in consequence of oxidation by the atmospheric oxygen. Brighten it 
again with sand paper and again connect the poles of the battery. 
Shorten the wire this time until it fuses, apparently boils, and finally MAGNETIC EFFECTS OP THE CURRENT. 
33 
burns in two. Iron is sometimes used for the “ cautery loop ”asit is 
very much cheaper than platinum. It is, however, much more liable to 
burn off during the operation. But even platinum will behave in almost 
exactly the same way if subjected to too strong a current. Remember 
this if you do not wish to have a very awkward accident happen during 
an important operation. Platinum can be as easily melted by the elec- 
tric current as can lead by the blast lamp. 
Exp. 57. Make a small cautery like the model shown. Be careful 
not to melt it the first time you attach it to the battery. 
Exp. 58. Connect this little cautery with a battery of one or two 
cells and notice the effect of battery polarization. The wire first glows 
intensely and then becomes a dull red—perhaps even shows no glow 
after being a few moments on the closed circuit. 
Exp. 59. Try to heat the little cautery with the six cells gravity 
battery. This battery has at least three times the Eof two bichromate 
cells in m. a., and yet it fails to heat the cautery. Explain why. 
Exp. 60. Observe the effect of raising or lowering the battery plates 
in the liquid by attaching the little cautery to one or two cells. Let 
one student raise and lower the plates while the other holds the cautery. 
This is one of the methods used to regulate the current of a cautery 
battery. 
Exp. 61. Use enough battery to cause the cautery to glow brightly 
and note the reading of the G included in the circuit. Now immerse 
one-half of the cautery (say the right hand half) in water or press that 
half against very wet paper. Notice the cooling effect on the right 
hand half—the increase in the current as shown by the G—and the in- 
creased glow of the left hand half of the cautery in consequence of this 
increase in the strength of the current. Explain it. A similar effect 
attends the use of the cautery loop in surgery and constitutes one of the 
serious difficulties in the practical application of the galvano-cautery, as 
in some cases the uncooled half may even be melted as soon as the oper- 
ation has begun. These effects are less marked when an excess of bat- 
tery power is used and the current cut down by means of a rheostat, as 
recommended in the text, than when the regulation of the current is 
effected entirely by the raising and lowering of the plates. Why 
should it be so ? 
22. Magnetic Effects of the Current.—As many 
electrical instruments depend upon the power of the current to 
induce magnetism in soft iron a very brief outline of electro- 34 
MAGNETIC EFFECTS OF THE CURRENT. 
magnetism will here be given. The following are the most im- 
portant laws: 
1. A piece o£ untempered iron, surrounded by a helix of 
wire, becomes a magnet while a current is flowing through the 
helix. 
2. The strength of this electro-magnet is proportioned to 
the number of turns in the helix and to the strength of the 
current. This law’ only hold while the magnet is still unsai- 
urated. 
3. Upon interrupting the current the induced magnetism in- 
stantly disappears. All ordinary iron, however, retains a slight 
trace of permanent magnetism which often causes the armature 
or vibrating hammer of automatic interrupters to “stick” even 
after the current has been stopped. This sticking may be pre- 
vented by pasting a little piece of paper upon the end of the 
magnet so as to prevent contact between magnet and armature. 
4. If the iron be removed from the helix the latter will still 
act, when the current is flowing, like an electro-magnet, but its 
magnetism will be many times less than when the iron core is 
present. [T. 326 to 330—8. B. 52, 53.—Upon the use of elec- 
tro-magnets in removing pieces of iron from the eye, etc., see 
B. R. 736.] 
EXPERIMENTS. 
Exp. 62. Cover a piece of soft iron rod about 4 inches long with pa- 
per. Then wind upon it a single layer of copper wire, not allowing the 
coils to touch each other. Using a few nails as an indicator, convince 
yourself of the following facts; 
1. The magnetism appears instantly upon the closing of the circuit. 
3. A slight trace of magnetism, called the “residual magnetism,” 
remains. You may have to balance a nail on a knife edge or suspend it 
by a thread, in order to prove this fact. 
2. It disappears instantly upon the interruption of the current. 
Exp. 63. The induced magnetism is proportional to the number of 
turns of wire in the helix. Prove by placing the iron in an east and 
west direction upon the table and far enough away from the G to cause 
a deflection of 45° when the current is flowing round the helix. The G, 
of course, is not to be in circuit. Now shift the wire from the battery 
along the coils of the helix and notice the gradual diminution of mag- 
netism as the number of coils in circuit is lessened. THE INDUCTION COIL. 
35 
Exp. 64. With the G and the electro-magnet in the same relative 
position as in Exp. 63, change the strength of the current by using 1 2 
and 3 cells in m. a. or by inserting a resistance coil in the circuit. No- 
tice the change in magnetism due to changes in current. Also observe 
the fact that strong currents are needed to produce strong electromag- 
nets. If a strong current is not used the helix must be made of a very 
large number of turns of fine wire, i. e., we must compensate for the 
weakness of the current by greatly increasing the number of turns in 
the helix. 
Exp. 65. With the same relative arrangement of G and magnet as 
in Exp, 63, prove the magnetic character of a helix by carefully with- 
drawing the core of iron from the coil. Observe how much weaker the 
magnetism has become by the removal of the iron. You may even have 
to bring the helix a little nearer the needle in order to get any evidence 
of its magnetic properties. 
23. The Induction Coil.—lt lies beyond tbe purpose 
of this book to describe fully the construction and theory of the 
induction coil nor is such description necessary as quite full ac- 
counts of the instrument will be found in the works mentioned 
in the following references. Moreover an actual inspection of 
the coils in the laboratory will give a far better idea of their 
construction than can any written description. [T. 398, 404. 
B. 8., especially recommended, 54 to 60; 292 to 304,—Jenkin’s 
“Electricity and Magnetism,” p. 289,—Larden’s “Electricity,” 
p. 268.] 
A short account of the various currents furnished by the 
coil will here be given. 
There are three quite distinct classes of induction coils. 
Class I.—This is the coil usually described in text books 
upon electricity and is intended for scientific researches requir- 
ing the exceedingly high electro-motive force which is furnished 
by static electric machines. The celebrated English coil, made 
by Apps of London, which gives a spark forty-two inches in 
length is the most striking example of this class. 
Class lI.—To this class belong the coils employed in Phys- 
iological research. They give almost no spark but admit of a 36 
THE INDUCTION COIL. 
wide range of adjustments for modifying tlie strength and char- 
acter of the current. 
Class lll.—This class is represented by the common Medi- 
cal Induction Coil. The current is practically the same as that 
of Class 11, but does not, as a rule, admit of so gradual and wide 
a change in strength and character. The instrument is, how- 
ever, much more portable, being mounted in a neat case con- 
taining battery, electrodes, conducting cords, etc., and it is to 
this class especially that the following remarks apply. 
The Induction Coil gives two different currents known re- 
spectively as the Primary (also called Extra) Current and the 
Secondary current. These two currents are sometimes com- 
bined, giving what might be called a third current which, how- 
ever, does not differ sufficiently from the Secondary to entitle it 
to a separate consideration. 
Besides the Primary and Secondary currents there is of course 
the current from the one or two galvanic cells which are used to 
operate the coil. This battery current is not administered to 
the patient but serves only to generate the other two. 
The character of these three currents, namely, the Battery 
current, the Primary, the Secondary, may be graphically rep- 
resented by the following diagram; 
I is the graphical representation of a perfectly continuous 
galvanic current such as is used in electrolysis. 
II represents the current from the battery which operates 
the coil. It is an interrupted current and all of the momentary 
currents are flowing in the same direction round the primary THE INDUCTION COIL. 
37 
coil of the instrument, “b” shows the state of things daring 
the fraction of a second in which the primary circuit is closed 
by the contact of the vibrating hammer and the adjusting screw 
of the interrupter, “a” represents the state of affairs during 
the fraction of a second in which the current from the battery 
is interrupted. 
11l shows the character of the “Primary” or “Extra cur- 
rent.” This current is generated in the primary wire just at 
the instant of cutting off the battery current. It is this cur- 
rent which causes the spark between the hammer and adjusting 
screw of the interrupter. It is always produced when an electro- 
magnet loses its magnetism upon the interruption of the mag- 
netizing current. Electric bells, dental mallets, in fact every 
piece of apparatus in which an elhctro-magnet is rapidly made 
and unmade gives this extra current as a matter of necessity 
and in case of emergency an electric bell might be employed 
as an induction coil by one who thoroughly understands the 
principles of the instrument. In most pieces of apparatus this 
extra-current is an evil since it tends to burn out the platinum 
contact points of the automatic make and break, but in the 
Medical Induction Coil it is turned to account and constitutes 
the weakest current which the instrument will give. Notice 
that it is an interrupted current in which all the little impulses 
are flowing in the same direction. It has a higher electro- 
motive force that has the battery which works the coil but U 
does not represent any more electrical energy nor, indeed, as 
much since something is always lost in electrical friction. 
What is gained in electromotive force is lost in time. The in- 
duction coil does not create energy, it simply transforms a cer- 
tain amount of electricity of low electromotive force into an 
equivalent amount of electricity of high electromotive force, 
and what is gained in Eis always lost in time. The total time 
during which the extra current is actually flowing, is probably 
twenty-five or fifty times less than the apparent time, i. e. a half 
hours’ or an hours’ use of the extra current represents only 
about one minute of continuous current. Hence it is, among 38 
THE INDUCTION COIL. 
other reasons, that the extra current (more commonly called 
primary current)] is not suitable for surgical electrolysis, al- 
though it ivill to a slight extent discompose fluids and produce 
the other effects of the galvanic current. 
1Y is intended to show the character of the secondary cur- 
rent. It is an interrupted, alternating current. The width of 
the arrows in the diagram is intended to represent the electro- 
motive force, and their length the duration of the successive 
impulses which go to make up the current. 
An inspection of the figure shows that the secondary cur- 
rent is composed of two sets of impulses which are flowing in 
opposite directions. These two sets differ in electromotive 
force, those which are produced at the break of the battery cur- 
rent having a higher E than those produced at the make. The 
latter, however, have a slightly longer duration, so that the total 
amount of energy represented by the two sets is practically the 
same. It follows, then, that this current will not electrolyze 
fluids, magnetise iron nor deflect the galvanometer needle, since 
the effect of one little impulse is immediately counteracted by 
the next one flowing in the opposite direction. 
On account of the alternating character of the secondary 
current, it has, properly speaking, no such thing as a positive 
or negative pole. If one set of the little impulses could be sup- 
pressed (say, for example, the ones marked 1), then there would 
be a true polarity of the secondary current. In the large coils 
of Class I such a suppression actually occurs, but in the coils 
of Classes II and 111 this is not the case except in a very slight 
degree. In consequence of this very slight suppression, and 
because one set of impulses has a, higher E than the other, 
most medical coils possess a slight differential action at the two 
poles of the secondary. This can be observed by taking the 
electrodes in the hands, when in most cases one wrist will expe- 
rience a rather stronger sensation than the other. The stronger 
sensation is produced by the negative pole of that set of im- 
pulses which has the higher electromotive force. 
The characteristics of the two currents of the induction coil 
may be summarized as follows: THE INDUCTION COIL. 
39 
1. Both currents are intermittent but only the Sis alter- 
nating. 
2. The P has a true polarity and will produce in general 
the effects of the continuous current but in a much less degree; 
while the secondary has only a pseudo-polarity and will not 
produce the effects of a continuous current. 
3. The electromotive force of the Sis much greater than 
that of the P which itself has many times the force of the bat- 
tery used in working the coil. 
4. The actual amount of energy of the P and Sis rather 
less than that of the battery cell which works the coil so that 
the physical effects of these currents is less than those produced 
by one galvanic cell. 
5. The physiological effects, however, are vastly greater 
than those produced by a single galvanic cell, since in this case 
the current is employed to call into action the forces of the ani- 
mal organism and does not itself supply the energy which is 
actually called forth. 
EXPERIMENTS. 
Exp. 66. Examine the model induction coil. This model is intended 
to show only the primary circuit and the automatic interrupter. It has 
no draw tube and no secondary coil and consequently gives only the 
primary (or extra) current. Trace the path of the battery current and 
also that of the primary. Study the construction and theory of the in- 
terrupter. Finally take the primary current through your arms, using 
only one cell to operate the coil. 
Exp. 67. Examine the electric bell and notice the general similarity 
of its construction to that of the interrupter of the coil. Notice the 
spark produced by the extra current. Study out how you can attach 
the electrodes to the bell so as to take this extra current through your 
arms. Use only one cell to work it. 
Exp. 68. Using the model coil prove that the primary current is 
felt only at the break of the battery current by carefully working the 
hammer back and forth by hand. 
Exp. 69. The draw tube weakens the induced currents by itself ab- 
sorbing the inductive influence. A current is induced around the tube 
instead of in the coils of wire. A tube split along its length will not 
reduce the strength of the induced currents. Prove this by slipping 40 
MAGNETO-ELECTRIC MACHINES. 
over the model coil first a complete tube and then a split tube. Notice 
that it is not necessary to have the draw tube next to the core. Even 
when placed outside of the primary wire it will reduce the strength of 
the primary current. In general, any continuous metallic conductor 
surrounding an induction coil, whether such conductor be next to the 
core or outside of both the coils, will reduce the strength of both the 
induced currents. Ignorance or disregard of this fact upon the part of 
some manufacturers renders several instruments in the market less 
powerful than they would otherwise be. In some coils the draw tube 
is very large and incloses both the primary and secondary wires as well 
as the core. 
Exp. 70. Examine a regular medical coil and take the various cur- 
rents which it gives. Prove that the secondary current is induced at 
both the make and break contacts by working the interrupter by hand. 
iN'otice how much the stronger the break impulse is. Observe, further- 
more, the difference in the two poles of the secondary—the negative 
giving the most painful sensation. By changing the electrodes from 
one hand to the other this will be brought out more plainly. 
Exp. 71. Prove that the secondary will not deflect the G( be care- 
ful that the coil is not so near the G as to exert a magnetic influ- 
ence upon the needle) by sending it through the upper coil of the instru- 
ment. 
Exp. 72. The secondary will not decompose electrolytes. Try it 
with a solution of copper sulphate, using the platinum electrodes. 
Exp. 73. Using the large dissected coil, study the effect of slowly 
removing the secondary wire. Observe the gradual diminution of the 
current—which nevertheless is still appreciable after the coil has been 
entirely drawn off from the primary. This method of modifying the 
induced current is much used in instruments intended for physiological 
research. 
24. Magneto-Electric Machines.—The essential 
thing in an induction coil is the rapid making and unmaking of 
an electro-magnet within a coil of wire. Any mechanical or 
electrical arrangement in which this is done will furnish an 
induced current in all respects similar to the secondary current 
of the regular medical induction coil. A magneto-electric ma- 
chine is an instrument in which the core of soft iron is alter- 
nately magnetized and de-magnetized by the approach and reces- 
sion of a powerful permanent steel magnet. In the usual form MAGNETO-ELECTRIC MACHINES. 
41 
in which this instrument is made there are two cores with their 
surrounding coils, instead of only one as in the induction coil, 
and these coils rather than the permanent magnet are movable. 
The principle, however, is the same—the cores are alternately 
rapidly magnetized and de-magnetized, thereby inducing a current 
in the surrounding wires. This induced current is an inter- 
rupted, alternating current but the successive impulses do not 
begin and end as suddenly as they do in the induction coil. 
Now the stimulating effect of the current depends upon the 
suddenness with which these impulses begin and cease and ac- 
cordingly all magneto-electric machines are provided with com- 
mutators or with some other mechanical device for interrupting 
or short-circuiting the induced current at least once in every 
revolution of the coils. This gives the necessary suddenness to 
the make and break of the little component impulses and ren- 
ders the current powerfully stimulating when the machine is 
driven rapidly. The commutator of some of these machines is 
sometimes so constructed as .to turn all the little impulses 
(which are actually alternating in direction in the coils) into 
the same general direction in the outside circuit. This renders 
the current quite similar to (but not so smooth as) the simple 
galvanic current. The large magneto machine upon the side 
table is one of this kind and will decompose water and produce 
the other effects of the continuous current. 
Magneto-electric machines require no battery with its ever- 
liable-to-be-spilled-fluid and in this respect is superior to an 
induction coil. In all other particulars however they are much 
inferior to the coil. They do not give as steady a current nor 
can the current be as gradually tempered in strength from the 
weakest up to the strongest which the instrument will furnish. 
Moreover an assistant must always be at hand to turn the ma- 
chine while the operator himself attends to the electrodes. 
The machine, too, is more liable than the induction coil to get 
out of order—in consequence probably of the necessity of a 
friction contact between the revolving coils and the outside 
circuit. 42 
ELECTRICAL TESTING. 
EXPERIMENTS. 
Exp. 74. Examine the two magneto-machines and trace the circuit 
traversed by the induced current. Be sure that you understand the 
manner in which the commutator of the large machine turns all the 
little alternating impulses into one common direction in the outside 
circuit. Notice, too, the method of interrupting the current in the two 
machines so as to render it stimulating. 
Exp. 75. Adjust the larger instrument so that the current is not 
interrupted and then take the current through your arms. You scarcely 
feel it. Now put on the interrupter and notice that the current is too 
painful to be taken if the machine be turned rapidly although the quan- 
tity of electricity is very much less in this case than when the interrupter 
vms not used. 
Exp. 76. The large machine will decompose water, copper sulphate 
etc. Try it. This machine might accordingly be used in surgical elec- 
trolysis, although it would not be nearly as effective as a battery of a 
dozen two-ounce bichromate cells. 
Exp. 77. The small machine gives an alternating current and will 
not decompose electrolytes. Try it. Notice how the current is modified 
by means of the movable armature. No special provision is made in 
the large machine for modifying the strength of the current. 
In all magneto-electric machines the strength of the current in- 
creases with the speed. 
25. Electrical Testing-.—Any defect in electrical ap- 
paratus which prevents its working properly is known, in tech- 
nical language, as a “fault.” Some knowledge of the nature 
of the faults most liable to occur and of the methods by which 
their presence and location can be determined is absolutely in- 
dispensable to one who expects to make a practical use of elec- 
tricity. A few suggestions upon the subject of electrical test- 
ing will accordingly be given. 
Whenever a piece of electrical apparatus fails to work satis- 
factorily, some one of the following faults is probably the cause. 
In testing for some of these faults it is necessary to use an 
independent battery and galvanometer which are known to be 
in good working order. One cell of any reliable battery is suf- 
ficient. Connect one of its poles with one of the binding 
screws of the G, and to the other pole of the battery and ELECTRICAL TESTING. 
43 
binding screw of the G attach two rather small flexible wires 
To the free ends of these wires fasten securely (by soldering or 
by carefully twisting the cleaned wires about the eye ends) two 
medium sized needles. These needles will be called “explor- 
ing needles” in the following directions. When they are made 
to touch any two pieces of metal which are in electrical con- 
nection with each other, a deflection of the G will evidently 
occur. Needles are better than the free ends of the wire be- 
cause they enable us to make assured contact with the wire 
of silk and cotton covered conductors and with those metallic 
parts of an instrument which are covered with lacquer or var- 
nish without injuring or removing these insulating materials. 
1. Imperfect Carbon Connection.-^-This is a very common 
cause of an insufficient current when using a Bunsen battery, 
and is readily corrected by rubbing together the carbon and its 
connector so as to secure clean surfaces of contact. Wetting 
the carbon slightly often improves the contact. 
In bichromate cells the carbons are usually fastened perma- 
nently to a metal mounting which in time may become corroded 
by the creeping up of the acid. In a well made battery this is 
prevented by thoroughly soaking the upper end of the carbon in 
hot paraffin and by carefully covering the whole joint with some 
acid-proof varnish or wax. 
To test a carbon connection place both the exploring needles 
firmly upon the carbon and note the G reading. Then press 
one of the needles on the metal to which the carbon is fastened. 
The deflection should be as great or even greater than before. 
2. Exhausted Fluids.—In Bunsen’s battery the nitric acid 
is more likely to be at fault, and may be tested with a little 
piece of zinc. Strong acid will attack zinc almost instantly 
with very copious evolution of red fumes. Bichromate fluid is 
good as long as it retains a trace of red or brown color. That 
which has become entirely green is exhausted and works no 
better than dilute sulphuric acid. 
The fluid of sal-ammoniac batteries is best tested by replac- 
ing it with fresh fluid. 44 
ELECTRICAL TESTING. 
Dilute sulphuric acid may be tested with a piece of zinc. 
Strong effervescence should take place after two minutes’ 
immersion. 
3. Poor Porous Cup.—A porous jar may cause high bat- 
tery resistance if it is not sufficiently porous. A good jar 
filled with water should lose at least one-sixth of it in 24 
hours by leakage. Another test is to replace a suspected jar 
with one which is known to be right. 
4. Imperfect Contact a,t Binding Screws, Line Connectors, or 
between wires carelessly twisted together.—A fault of this kind 
is generally quickly dectected and corrected by tightening all the 
binding screws and connectors in the circuit. Before wires are 
twisted together they should be rubbed bright with a piece of 
sand or emery paper. Simply laying one wire upon another 
shoidd never be depended upon as a means of contact. To make 
the connection sure the wires must be freshly scraped and firmly 
twisted together. The use of line connectors is far preferable 
to the twisting together of wires. 
5. A Complete Interruption of the Circuit in consequence 
of a break in the wire or soldered connections.—A fault of this 
character is best detected by testing the whole circuit, section 
by section, with the exploring needles. This can be very quickly 
done with an exploring battery arranged as described above. 
6. Binding Posts sometimes become insulated from the 
underneath ivires.—This is frequently caused by the binding 
post turning a little in its hole and thereby breaking the wire 
or pushing it out of position. Test by putting one exploring 
needle against the post and the other against the wire under- 
neath. 
7. Broken Strands of Wire in the silk-covered cords at- 
tached to electrodes are often an unsuspected cause of trouble. 
In a fault of this kind the current is frequently intermittent, some- 
times flowing normally and then suddenly ceasing without any 
apparent cause. Such breakage is especially apt to occur close 
up to the little metal tips, which are attached to the cords, in 
consequence of the frequent bending of the cord at these points. ELECTRICAL TESTING. 
45 
A loose attachment of the cords to the tips may also result in 
a break in the circuit. Test by placing the needles in contact 
with the tips or with the middle of the suspected cord and each 
tip in turn. 
8. A Cross-connection or Short Circuit.—This may happen 
in Grenet cells in consequence of the zincs swinging around 
into contact with the carbon plates. A Gravity or Daniell’s cell 
may become short circuited by a deposited thread of copper 
running from one plate to the other. 
A partial short circuit may occur in those batteries in which 
the plates are fastened permanently to a cap or cover on top of 
the jar in consequence of the cap becoming covered or soaked 
with battery fluid or water. 
Test by taking the plates out of the fluid and touching the 
exploring needles to the two plates of the suspected cell; a de- 
flection of the G indicates an imperfect insulation of the posi- 
tive and negative plates. 
This difficulty is corrected by thoroughly drying the parts 
and soaking them in hot paraffin. 
9. Corroded (oxidized) Platinum Points.—This is the most 
common cause of the stopping of an induction coil, electric 
bell, mallet, etc., etc., and is both detected and corrected by 
rubbing the points very slightly with a, fine file. Fine sand or 
emery paper will also do, but a thin fine file is better, in that it 
does not leave a fine grit imbedded in the metal to be subse- 
quently fused, by the extra current spark, into a thin insulating 
coating of glass. 
10. Corroded Surfaces in Switches arid Commutatators: or 
between sliding contacts of any kind—Some forms of the 
Grenet cell depend upon the friction contact of a brass rod 
with its surrounding sleeve for a zinc connection. Such a con- 
tact is very uncertain. In general the larger the surfaces in 
contact the less certain is the connection. Test all such sus- 
pected connections by putting the exploring needles upon the 
two pieces of metal which are supposed to be in electrical con- 
tact. If no current flows the contact is not complete and the 46 
ELECTRICAL TESTING. 
metals must be cleaned with a little fine sand or emery 
paper. This is a very common fault and must be carefully 
watched for. 
11. Bichromate Batteries sometimes refuse to give a good 
current for several minutes after the plates have been lowered, 
in consequence of a deposit of crystals upon the surface of the 
plates. Hot water will remove such a deposit immediately. 
Such a deposit indicates too strong a battery fluid. Add more 
water or rinse off the plates after using the battery. 
Sal-ammoniac Cells sometimes fail from a similar deposit 
upon the zinc rods. The zinc rods of these cells fire frequently 
eaten off just at the surface of the fluid. A coat of paraffin at 
this point will prevent this difficulty. 
12. A frequent cause of failure in using electrical apparatus 
arises from the attempt to employ an insufficient battery power 
for the particular instrument or work in hand. This is not 
strictly a fault, and can be discovered only by making certain 
that there is no other cause present capable of accounting for 
the failure. Failure from this cause is most liable to happen 
with the galvano-cautery and electric motors of various kinds. 
EXPERIMENTS. 
Exp. 78. Convince yourself of the unreliability of the contact ob- 
tained by simply laying two wires across each other, by watching the 
needle of your G when such a contact is made. Kotice that the needle 
is almost constantly on the move, sometimes dropping back to zero and 
then suddenly starting up and perhaps revolving several times around 
as the contact is alternately made and broken. 
Exps. 79 to 91. In order to give some practice in electrical testing a 
series of defective batteries and other instruments has been prepared. 
Each student is expected to take one of them to his desk and make a 
systematic examination in order to find out the exact character and 
location of the fault. Keep a record of the number of the apparatus 
and of the nature of the fault, but do not correct the defect. After 
completing the examination, return the apparatus to the side table in 
the same condition in which you found it. Examine as many as you 
have time for during the afternoon. Fit up your exploring battery the 
first thing according to the directions in the text. Your Yolta’s cell 
will serve admirably for this purpose. PROBLEMS. 
47 
26. Problems.—In order to fix some of the fundamen- 
tal principles and facts more firmly in the memory and to give 
facility in applying them to particular cases, a few general prob- 
lems will here be given. 
As these problems are given out from day to day by the in- 
structor, numerical values will be assigned to the letters used 
in the text. 
PROBLEMS, 
Prob. 1. A certain battery consists of s cells coupled in series. 
Each cell has [an Eof t volts and a R of u ohms. The external resis- 
tance is v ohms. What is the strength of the current in amperes ? 
Prob. 2. A battery of s cells in m, a. sends its current through an 
external resistance of t ohms. Each cell has an Eof u volts and aR of 
v ohms. 
(1) What is the Rof the battery ? 
(2) What is its E ? 
(3) What is the strength of the current? 
Prob. 3. A certain battery is coupled sin series and tinm. a. Each 
cell has aßof u ohms and an Eof v volts. The external circuit has a 
resistance of w ohms. 
(1) How many cells does the battery contain ? 
(2) What is the Eof the battery? 
(3) What is its R ? 
(4) What is the current in amperes ? 
Prob. 4. A battery of s cells in series and t cells in m. a. sends its 
entire current through an electrolytic cell containing acidulated water. 
The resistance of the electrolyte and conducting wires is u ohms. The 
inverse E due to polarization is 1T50 volts. The E and Rof each battery 
cell is v volts and w ohms respectively. 
(5) What is the current flowing through each cell? 
(1) What is the C, in milliamperes, which flows through the elec- 
trolyte ? 
(2) What is the Cin each battery cell? 
(3) How many grains of water will be decomposed in one hour? 
Prob. 5. Each cell of a certain battery, coupled in series, has an E 
of s volts and aR of t ohms. The external resistance is a piece of iron 
wire u feet long and v inch in diameter. The current is w milliamperes. 
How many cells are there in the battery ? 
Pros. 6. A battery of s gravity cells is coupled tin series and uin 
m. a. The Eof each cell is two volts and its Ris one ohm. 48 
PROBLEMS. 
The current passes from the battery through v feet of brass wire 
haying a diameter of w inch. Then through an electrolyte of copper 
sulphate having an inverse E of isv volt and a resistance of x ohms. 
The current then returns to the battery upon a platinum wire y inches 
long and 0 inch diameter. 
(1) What C flows through the copper sulphate? 
(2) How long will it take to deposit a troy ounce of pure copper ? 
(3) How many ounces of copper will be deposited upon the copper 
plates of the battery during the deposition of one ounce of copper 
in the electrolytic cell. 
(4) How can the inverse E of yfr volt in the copper sulphate cell be 
avoided, without taking the electrolytic cell out of the circuit? 
(5) How much zinc and how much copper sulphate (crystallized) 
would be consumed in the battery during the deposition of one 
pound of pure copper in the electrolytic cell. 
Prob. 7. A battery of s cells in series sends its current through a 
telegraph line of iron wire having a diameter of (inch. A non-polariz- 
able voltameter, having a resistance of u ohms, when placed in the cir- 
cuit, deposits v grains of copper in one hour. Each battery cell has an E 
of w volts and aEof x ohms. Erom these data find 
(1) The strength of the current. 
(2) The length of the telegraph wire. 
Prob. 8. A battery of s cells in m. a. has its poles connected by 
three wires of the following material and dimensions: 
Ist. t yards of copper wire u inch in diameter. 
2nd. v feet of German silver wire w inch in diameter. 
3rd. x inches of platinum wire y inch in diameter. 
These wires are laid in parallel, i. e., they form a divided circuit of 
three branches. The E and E of each battery cell is lyV volts and 
ohm respectively. 
(1) What is the total current? 
(2) What is the current in each of the above wires ? 
Prob. 9. One Leclanche cell, having an Eof lT4TI volts and an Eof 
ohm, is just strong enough to work a call bell of s ohms resistance when 
connected to the bell by wires of no appreciable resistance. I wish to 
put the bell in a stable situated one mile from my office. The wire run- 
ning to the stable is made of iron and is t inch in diameter. The return 
circuit is the earth and has no appreciable resistance. 
(1) How many Leclanche cells must I use to work the bell ? 
(2) What size copper wire, put up in place of the iron wire, will en- 
able me to work the bell with two Leclanche cells ? PROBLEMS. 
49 
(3) What size iron wire, stretched beside the first one and used in 
parallel with it will enable me to work the bell with two Le- 
clanche cells ? 
(4) How many gravity cells, each having aR of two ohms and an E 
of one volt would work the bell over the line wire already up ? 
Prob. 10. A battery of twenty gravity cells, each cell having an E 
of one volt and a R of two ohms, is coupled ten in series and two in m. 
a. The current passes from the battery through a galvanometer of five 
ohms resistance and then divides and passes through a divided circuit, 
one branch of which consists of x feet of iron wire having a diameter 
of of an inch. The other branch contains an electrolytic cell, filled 
with a solution of copper sulphate, having a resistance of five ohms and 
electrodes which are non-polarizable. Upon closing the circuit the 
galvanometer indicates a current of .5333 + ampere, and a penny- 
weight of pure copper is deposited in the electrolytic cell in three hours 
and twenty minutes. What is the length of the iron wire which forms 
one branch of the circuit? QUESTIONS. 
1. What materials are consumed in Yolta’s battery? 
2. What chemical products are formed in Yolta’s cell? 
3. What connection is there between the amount of zinc con- 
sumed in a battery and the strength of the current? 
4. What is the strength of battery sulphuric acid? 
5. What is the cause of inconstancy in the currents of some 
batteries ? 
6. What is the “local action” of a battery and what harm 
does it do? How is local action prevented? 
7. Why are the zincs of some batteries amalgamated and 
those of others not? 
8. How can a zinc be amalgamated without using metallic 
mercury? 
9. What is “polarization” of the battery? 
10. How is it prevented in Bunsen’s cell? In the gravity cell? 
In the Bichromate of Potash cell? 
11. Which of the batteries mentioned in the text is least apt 
to polarize? 
12. Give the formula for making Bichromate fluid. 
13. For what purpose is the Leclanche battery especially fit- 
ted, and why? 
14. What fluid is used in the Leclanche cell? 
15. What materials are consumed and products formed in the 
Darnell’s cell? In Bunsen’s cell? 
16. Why is Bichromate fliud which has become green no 
longer good? 
17. What is the purpose of the porous jars used in some bat- 
teries? 
18. What is soldering fluid? QUESTIONS, 
51 
19. What soldering fluid is used is soldering iron to brass? 
20. Why ought every trace of soldering fluid to be washed off 
after soldering? 
21. Why is a gravity battery unsuitable for the galvano-cau- 
tery ? Why is the Leclanche also unsuitable? 
22. What do you understand by the term “electromotive 
force?” 
23. Give the Eof the following cells: Bunsen’s, Yolta’s, Le- 
* clanche’s, Gravity, Bichromate of Potash. 
24. Why should not the clamps and connections be left fast- 
ened to Bunsen carbons? 
25. What causes the cracking of porous cups, and how may 
such cracking be avoided? 
26. Will it do to add a mercury salt to every form of battery 
for the purpose of keeping the zinc well amalgamated? 
What battery is an exception ? 
27. Mention three important precautions to be observed in 
using a galvanometer. 
28. What is the approximate resistance of a medium sized 
Bunsen cell? Bichromate cell? Gravity cell? 
29. How does a large cell differ from a small one in its electri- 
cal properties? 
30. Does the depth of fluid in a cell in any way affect its 
power? 
31. Some cells have two carbon plates instead of one. Why is 
this an advantage? 
32. Some large sized cells contain several carbons and several 
zincs. Does such a cell have any more E than a common 
cell? For what purpose are such cells employed and why 
are so many plates used? 
33. Are there any conceivable conditions under which a cell no 
larger than a thimble would give as good a current as a 
cell as large as a barrel? What are those conditions? 
34. When are large cells much to be preferred to small ones 
and when are they no better than small ones? 
35. What are the three general ways in which battery cells 
may be coupled together? 52 
QUESTIONS. 
36. Under what circumstances would a battery of 1,000 cells 
in series give no greater a current than one cell? 
37. Under what circumstances would 1,000 cells in m. a. give 
no greater a current than one cell? 
38. Which is the best method of coupling cells? 
39. How does coupling in series affect electromotive power? 
How the resistance of the battery? 
40. How are electromotive force and resistance affected by 
coupling in m. a. ? 
41. How would you couple a battery of eight cells to treat 
a case of facial neuralgia? 
42. When would you couple a battery in m. a. instead of in 
series? 
43. What general rule have we for coupling a battery so as to 
obtain the maximum current which it will give? 
44. Under what circumstances does a Bichromate cell show a 
good deal of polarization? 
45. How may this polarization be lessened? 
46. Upon what conditions does the strength of a current de- 
pend? 
47. When does the battery resistance play an important part 
in determining the strength of the current and when does 
it not? 
. 48. Give Ohm’s Law in its three most important forms. 
49. What is a calibrated galvanometer? 
50. What connection is there between the strength of the 
current and the deflection of the needle in a tangent galvan- 
ometer? 
51. What is a milliampere? A milliamperemeter ? 
52. What would be called a “moderate current” as currents 
go in the therapeutical uses of electricity? 
53. What is the approximate resistance of the human body 
from hand to hand? 
54. What is the approximate resistance between the needles in 
an ordinary case of surgical electrolysis? QUESTIONS. 
55. What is a divided circuit? 
56. According to what law does a current divide itself in pass- 
ing over a divided circuit? 
57. What is the relation between resistance and conductivity ? 
58. What is the equivalent resistance of a multiple conductor 
consisting of four strands of wire having respectively the 
resistance 1, 8, 5 and 20 ohms. 
59. If a total current of 100 milliamperes were flowing though 
this multiple conductor what would be the number of mil- 
liamperes flowing in each of the four strands. 
60. What is a shunt? 
61. How may the Incandescent Light current be adapted to a 
physician’s work? 
62. A certain galvanometer has a resistance of 15 ohms. 
What resistance must a shunt have in order that only A of 
the entire current shall go through the galvanometer 
when the latter is used in electrical measurements. 
63. Why cannot a current be confined to a muscle or nerve in 
using electricity therapeutically ? 
61. Are all liquids electrolytes? 
65. Does pure water conduct electricity ? 
66. What is an Anode? A Kathode? 
67. What are the ions in the electrolysis of acidulated water? 
68. At which electrode does oxygen appear? 
69. What is the relation between the amount of electrolysis 
and the strength of the current? 
70. How much water will a current of 10 milliamperes decom- 
pose in an hour? 
71. How strong a current would be required to deposit one 
ounce of electrolytic copper, from copper sulphate, in ten 
hours ? 
72. At which electrode are the metals liberated? 
73. What are “secondary products” in electrolysis? 
74. What are the primary products in the electrolysis of com- 
mon salt solution? 54 
QUESTIONS. 
75. What secondary products occur in the electrolysis of salt 
solution ? 
76. Explain why electrodes are corroded. 
77. Which electrode is corroded most ? Does either electrode 
escape corrosion entirely? 
78. Is the resistance of an electrolytic cell affected by the size 
of the electrodes or by the distance between them? 
79. What is “ polarization of the electrodes ”? 
80. What is the value of electrode polarization in surgical 
electrolysis ? 
81. What is the principle upon which electrodes are made non- 
polarizable? 
82. In surgical electrolysis have large battery cells any marked 
advantage over small ones? 
83. How should a battery be coupled for surgical electrolysis. 
84. At which electrode are acid products formed? 
85. Why is the kathode preferable to the anode in the extir- 
pation of hairs by electrolysis? 
86. Why should sponge or cloth covered electrodes be em- 
ployed when using the galvanic current upon a patient? 
87. Why should electrodes be wet in salt solution? 
88. Which pole of a galvanic battery causes the sharpest sen- 
sation or the most pain? 
89. With what material are electrolytic needles insulated and 
how is it put on so as not to peel off when the needles are 
used? 
90. Have platinum or gilded needles any great advantage over 
plain steel needles? 
91. What would be the effect of bringing the two needles used 
in a case of surgical electrolysis into contact within the 
tissues? 
92. How does the resistance of a wire vary with variations in 
its diameter? 
93. A certain bell circuit has a resistance of 25 ohms. The 
wire has a diameter of -fa of an inch. What diameter of 
wire must be used to reduce the resistance to one ohm. QUESTIONS. 
55 
94. In which of the following cases should quite heavy circuit 
wires be used and in which will quite small ones do as 
well as large: 
Ist. Electric door bell of low resistance. 
2d. Surgical electrolysis. 
3d, Galvano-cautery. 
4th. Telegraph “ Sounder ” of very high resistance. 
sth. Electric Dental Mallet. 
6th. Electric fuse in blasting operations. 
7th. Electro-magnet with coils of large size wire. 
Bth. “ General Galvanization ” of a patient with a battery 
of 10 cells. 
95. Give some approximate estimate of the strength of cur- 
rent required to heat a cautery. 
96. Why must a low resistance battery be used with the gal- 
vano-cautery? 
97. What are some of the important conditions to be fulfilled 
in making a galvano-cautery ? 
98. What is the connection between the heat developed in a 
conductor and its resistance? What between the heat and 
the strength of the current? 
99. Why is platinum used in the cautery rather than iron? 
100. Mention two kinds of battery which are not suitable for 
heating the cautery, and in each case tell why the battery 
is not suitable. 
101. How does the strength of an electro-magnet vary with 
changes in the strength of the current? 
102. How with changes in the number of coils of wire sur- 
rounding the magnet ? 
103. How many currents does the induction coil furnish and 
what are they called? 
104. What is the character of the primary current? What is 
the difference between primary current and extra current? 
105. Has the primary current a positive and negative polarity? 
106. Will the secondary current decompose water or produce 
surgical electrolysis ? 
107. Is there a difference in the poles of the secondary cur- 
rent? 56 
QUESTIONS. 
108. How does the quantity of electricity furnished by the 
induction coil compare with the quantity of the battery 
current? 
109. In respect to what quality is the induced current of the 
coil stronger than the battery current? 
110. What causes the spark at the end of the adjusting screw? 
111. Why does the draw tube modify the strength of the cur- 
rent ? 
112. Why do the cores of some induction coils consist of a 
bundle of iron wires instead of a solid iron rod? 
113. If the secondary coil is entirely insulated from the rest of 
the instrument explain how the electricity gets into it. 
114. Explain how the interrupter of the coil works. 
115. Why is the secondary coil made of a much finer wire than 
the primary coil? 
116. Why is the tip of the adjusting screw made of platinum? 
What is the little piece of metal upon the spring opposite 
the screw? 
117. What is the character of the current given by a common 
medical magneto-electric machine? 
118. Why is an induction coil better than an magneto-electric 
machine ? 
119. How is the current of the machine regulated? 
120. A Bunsen battery fails to give its due current. Mention 
two or three possible reasons for the failure. 
121. How can the corrosion of the metal fittings, to which the 
carbon is fastened in bichromate cells, be prevented? 
122. A call bell circuit suddenly ceases to work. Mention 
some of the more probable reasons why it has ceased. 
123. An induction coil with which you are working suddenly 
stops. What is the probable cause and how is it removed? 
124. Draw a diagram of the working parts of a call bell, show- 
ing the path of the current. Explain why the hammer 
keeps vibrating automatically. 
125. Upon attaching a cautery to its battery you fail to get 
more than a very dull red temperature. How would you 
attempt to remedy matters?