REPORT 
ON THE 
VENTILATION 
OF THE 
HALL OF REPRESENTATIVES, 
AND OF THE 
SOUTH WING OF THE CAPITOL 
OF THE 
UNITED STATES. 
TO PROF. JOS. HENRY, COL. T. LINCOLN CASEY, DR. J. S. BILLINGS, 
EDW. CLARK, ESQ., F. SCHUMANN, ESQ., 
COMMISSION, OF INQUIRY, ETC. 
ROBrAy'BRIGGS, C. E. 
PHILADELPHIA. 
PRESS OF HENRY B. A SIIM E A D, 
Nos. 1102 & 1104 Sansom Street. 
1876. REPORT 
ON 
VENTILATION OF HALL OF REPRESENTATIVES. 
Bit ROBERT BRIGGS, C.E. 
To Prof. Joseph Henry, Col. T. Lincoln Casey, Doctor J. S. 
Billings, Edward Clark, Esq., F. Schumann, Esq., 
Commission to examine into the Ventilation of the Hall of Representatives. 
Gentlemen:—In conformity with your request that I should give 
you a statement of the system and apparatus for ventilating and 
warming the Ilall of Representatives as originally proposed and con- 
structed, and after personal examination, its present condition and 
performance, I have to say : 
I. Regarding the original plans, that it was proposed to introduce 
to the Ilall, by means of an apparatus for this room only, from the 
most eligible point about the grounds of the Capitol, the most ample 
supply of fresh, pure air. 
The place selected from which the supply of fresh air was to be 
taken, was the esplanade or upper terrace at the northwest corner of 
the south wing of the New Building, between it and the Old Capitol, 
in the entering angles or recess formed by the connecting building; and 
from the ground level of this terrace, the air passed directly through 
regulated windows, into the room in the crypt containing the fan. 
The supply of air for the north wing—for the portion of the building occupied 
by the Senate, was taken from the corresponding point at the south-west corner of 
that wing, the same arguments as to suitability of place, attach to that choice of 
position. 
This locality was deemed pre-eminently advantageous. The pre- 
vailing winds of the District are westerly. It is of the rarest occur- 4 
Report on the Ventilation of the Hall of Representatives. 
rence that there is any but a short deviation from this direction ; 
perhaps not one entire day in forty does the wind come from the east- 
ward, or even from due north or south. The western front of the 
Capitol surmounts an elevation of ground above the level of Pennsyl- 
vania Avenue, and of the streets and open grounds beyond those ot 
the Capitol itself, of perhaps fifty feet height. The esplanade is 
is nearly level, but is only some thirty feet wide, and is at the top ot 
a steep terrace rise of thirty to thirty-five feet. The great extent of 
the Capitol building, (over 700 feet,) from north to south, thus forms 
a barrier to the westerly currents, which roll upward against it, and 
effectually prevent the fall of any vitiated air which may escape from 
the doors, windows or flues. Before this terrace there exists a wide 
park (800 to 1000 feet in width), carefully graded, and drained, and 
preserved in the most healthy condition by constant labor and atten- 
tion, shaded by numerous trees which absorb a portion of the heat of 
the air, and are still more valuable for the purpose of securing air for 
the house, in the interception of dust, from the streets beyond the 
grounds. 
The propriety of removal of the point for obtaining supply of 
pure air, further from the Capitol, and also the condition of 
air at different elevations as regards purity, was fully considered. 
The location of any more or less removed point of supply was 
obviously, from the configuration of the ground, restricted to either 
west or east of the Capitol, as the marshes then existing north or 
south (and yet existing to the south) were manifestly unsuitable for 
sources of pure air, either on the surface or with quite high towers 
(except some Washington monuments were designed for the purpose). 
The conditions of westerly winds referred to, would also demand that 
a point of supply on the east side should be either very far removed 
or very much elevated, if the emitted air from the Capitol should be 
certainly dispersed before the supposed mouth for supply of fresh air, 
were reached. In fact the statement of conditions alone makes it 
obvious, that of the two locations, the one to the west of the Capitol 
should be chosen; and the remaining questions must be examined as 
an accepted basis of a supply of air from this side. Removal from 
proximity to the building, supposed a tunnel connected to some open- 
ing or tower situated on the ground, below the terrace. Twenty years 
ago, at which time the decision as to source of fresh air supply was 
made, the Tiber was an open gulley taking the drainage of two square Report on the Ventilation of the Hall of Representatives. 
5 
miles of territory, then but sparsely covered by tenements—the canal 
was also a broad, stagnant, filthy pool; and the reservations outside 
the Capitol grounds were pestilent, undrained and ungraded marshes. 
The carrying of a tunnel down towards these abominations and placing 
of an opening near, or a little elevated above, the surface of the ground; 
getting nearer and nearer to the dusty Pennsylvania Avenue; sacri- 
ficing all the advantages of distance, and time for removal of dust, 
would not he approved; and even to-day, with the circumstances so 
changed in the enumerated conditions at that time, it is doubtful if 
mouth for entrance of air near the surface would meet commendation. 
A tower thus becomes the alternative. Its dimension is fixed by the 
quantity of air needed—40 feet square or 50 feet internal diameter, 
are the least dimensions requisite to furnish air to both wings and 
the Old Building together. Its height must be 35 to 40 feet to reach 
the top of the esplanade alone, and as much higher as might he con- 
ceived necessary to find the pure air uncontaminated from all im- 
purities. IIow high can this be conceived % This becomes the next 
question involved in the discussion, and it is answered by referring to 
the results of investigations made before 1855, and frequently re- 
peated since, upon the purity of air in cities at different elevations, 
the results of which can be briefly stated. There are great variations 
in the quality of air in different cities, arising from density of popu- 
lation, nature of fuel, character and avocations of the inhabitants; 
and again from climate, prevailing winds, and winds at the time of 
observation, hygrometic condition, normal or abnormal, etc., etc.; 
but .after the dispersion of impurity generated in any particular 
locality, the purest air is generally found from 6 to 40 feet, the most 
impure at 70 to 90 feet above the level of the ground, with gradation 
rising to balloon heights. Over any free or open places in a city the 
dispersion of local impurities is the more completely effected, and the 
uniformity of condition the more generally obtained ; but the elevated 
air is more impure, when the stratum of diffused chimney exhalation 
is reached, than it is below. 
The Londoner does not experience any great sense of purity of air 
from the top of St. Paul’s as a general rule; and the haze of any large 
city is perceptible for miles on a still day—the entire city is covered 
as with a blanket by an ascending and dispersing cloud, and receiving 
its fresh air from beneath from all sides. 
Upon a still day, a tower would manifestly offer little advantage 6 
Report on the Ventilation of the Hall of Representatives. 
in its elevation of the point of taking the air, as regards its purity, 
unless the height were over 100, and perhaps quite 200 feet or more; 
while on a windy day, in such a locality as that in which the United 
States Capitol is placed, the average condition of the air at any 
elevation above the ground would be established. 
The objection that the air is heated in traversing the stone surface 
of the esplanade before entering the fan mouth, can be admitted only 
in part; for the volume is so great that only the least portion of air 
comes in contact with the stones, the greater part of it by far, being 
taken directly from the space ; but the same objection attaches with 
equal or greater force to a masonry tower, which whenever exposed 
to the sun, will have an upwTard heated current rolling along and 
flowing up it, to be sucked in at the top. 
A tower or tunnel wTould have been unsightly; costly in first con- 
struction, expensive ever afterwards to draw the air through it, and 
open to the criticism of scientific men at all times without the possibility 
of logical support; and although it would have been a demonstration, 
and although it might meet the written authority of many who have 
considered ventilation, as a problem of what should be done in lieu of 
howr to do it, yet I am satisfied this statement of reasons will show 
the propriety of the original choice of the place for taking fresh pure 
air for the ventilation of the Capitol. 
The internal dimensions of the room, occupied as the Hall of Repre- 
sentatives, are 139 feet long (east and west); by 93 feet wide (north 
and south); by 36 feet average height (from general level of l,owTer 
floor, to the average surface of the under sides of the ceiling); the 
lower floor, where the seats and desks for the members of the House 
are placed, is 113 feet long by 67 feet wide, and is surrounded by re- 
tiring rooms and private vestibules under the galleries. The retiring 
rooms (coat rooms) are always open to the floor of the Hall, and re- 
ceive their ventilation from the Hall apparatus. The gallery walls 
are about 12 feet high, wTith a parapet, which makes them show7 about 
two feet more in height. The cubical contents of the entire room, 
with the coat rooms and vestibules, are, very nearly, 500,000 cubic 
feet. 
The South Wing of the United States Capitol is a building 230 feet 
long (east and west), by 135 feet wide (north and south), outside of the 
walls of enclosure; (there are extended porches on the east, south and Report on the Ventilation of the Hall of Representatives. 
7 
west sides, and a connecting building on the north side joins the main 
edifice, or “Old Capitol”); it is three stories in height, above the 
ground level, and the Hall is in the second and third stories, (the gal- 
leries opening from the third floor,) with a basement of dark rooms 
(intended for depositing stationery in the original allotment of rooms), 
under the floor of the Hall. 
The basement story is 20 feet in floor height, and there is a crypt 
of perfectly dry, vaulted rooms, beneath the ground floor of the entire 
building. On the east front of the Capitol, the ground is nearly level 
(having a slight rising grade eastwardly), and the basement story 
floor is elevated four or five feet above it. On the southern and west- 
ern fronts the ground falls off- rapidly, giving the esplanade and ter- 
race previously mentioned on the western front. 
The quantity of air determined upon was that of 30 cubic feet each 
minute per individual in the Hall in the coldest weather of winter, 
and of 60 cubic feet each minute per individual in the Hall, at other 
seasons, or when desired. The crowded capacity of the floor and 
galleries (the latter being occupied by seated persons) was estimated 
at 1600 individuals, and thus the minimum ventilation became 50,000 
cubic feet, and the maximum 100,000 cubic feet per minute. [See 
Appendix A.] 
These volumes of air were supplied by means of a large fan, 16 feet 
in external diameter, which was driven by an independent steam 
engine of proper dimensions. This fan and its engine are situated in 
the north-west corner room, of the cellar or crypt of the south wing 
of the Capitol. The fan was supposed to be required to overcome a 
total resistance, equivalent to about four-tenths or six-tenths of an inch 
of a column of water ; which corresponds to the pressure of air of two 
to three pounds upon the square foot: being the total resistance to the 
passage of the air which should proceed from the air ducts leading to 
the Hall; from the channels of distribution under the Hall floor; from 
the mouths of discharge of the registers into the Hall, and finally, 
from the floors through the Hall, out of the ceiling, and through the 
roof to the open air. With these resistances the fan was supposed, 
when running at the rate of 50 to 60 revolutions per minute to give 
the 50,000 cubic feet of air, and when running at 100 to 120 revolu- 
tions per minute to give the 100,000 cubic feet of air, required. 
The provisions for heating the air were fully equal to the largest 8 
Report on the Ventilation of the Hall of Representatives. 
demand, there being for this purpose, one main coil (in four separated 
parts) of wrought iron steam pipes, of one inch internal diameter, 
having a total length of 50,000 running feet (nearly 10 miles) of 
pipes ; which pipes have a total heating surface of 17,000 square feet. 
The air ducts from the fan to the coil, and from the coil to the Hall, 
were somewhat tortuous, being necessarily so, to obtain the requisite 
dimensions without encroachment upon the architectural arrangements 
of the building ; but they have the proper size, and are free from en- 
largements or angles, so as to afford an unrestricted flow for the air 
currents within them. 
The sources of power, the means of producing steam for the impulse 
of the air, and for heating it—the boilers—were ample in capacity. 
II. The choice of the system of ventilation was made by Gen. M. 
C. Meigs after long and due consideration, and was that known as a 
forced (or plenum) upivard system. 
The work on the Capitol Extension had been placed in the hands 
of General Meigs in March, 1852, after the commencement of the 
building, and after the construction had proceeded, to the “ completion 
of the cellars and arches to the basement floorand continued in his 
charge until October or November, 1859, at which time both wings 
of the buildings wTere occupied, the Hall of Representatives having 
been used throughout the session of 1858-9. 
Accompanying the first report of General Meigs (May, 1853, to the 
Secretary of War on the progress of work on the Capitol Extension), 
are notes of his primary investigations upon acoustics and ventilation, 
in which he proposed to adopt a forced downward ventilation for 
reasons stated, but subsequent study led to another conclusion. 
In June or July of 1855, while General Meigs was pursuing his investigations on 
the subject of ventilation of the Extension of the Capitol, he became acquainted 
with the late Mr. Joseph Nason, of New York. Mr. Nason was at that time un- 
questionably the best informed and most experienced person on Heating and 
Ventilation in the United States, and his practice had made him acquainted with 
the requirements of the climate which were not (and as yet are not) properly con- 
sidered in any publication on the subject. Mr. Nason’s eminent skill as a mechanic, 
his profound information, and his happiness in imparting it, commanded for him the 
position of a consulting engineer on this specialty beyond any person then or now 
living. He had been the founder of the system of steam heating by means of wrought 
iron steam pipes, now so generally employed in all countries; and his investigations 
and experience in ventilation had led to the adoption by him of mechanical appliances 
suited to meet the occasion, and which have formed the type of all subsequent Report on the Ventilation of the Hall of Representatives. 
9 
practice. With a highly inventive and appreciative mind, he was a keen observer 
and student, and his store of knowledge rose to that point, where with all his 
novelties of application he could not or did not claim the inventors rewards in 
patents. Yet it is not an exaggeration to say that all the essential details of con- 
struction now in common use in steam heating, with the highest refinement of 
shapes and the closest relation to absolute utility or cost of production, are unim- 
proved and substantially unchanged as they proceeded from Joseph Nason, and 
beside this, that nine-tenths of the patents of the past thirty years referring either 
to heating or ventilation apparatus or to any details, are founded upon or trench 
upon his accepted or discarded practice. Mr. Nason was a pupil (and student) of 
Jacob Perkins (an American mechanic of world-wide renown) of London, and he 
faithfully sustained the reputation and aided in the progress of the art of heating 
which Mr. Perkins established. Mr. Nason was consulted by General Meigs in the 
preparation of the plans for arrangement of apparatus used at the Capitol Extension. 
The following considerations are those which determined the prefer- 
ence for the system adopted : 
The comfortable temperature at which the Hall was to be kept was 
obviously at or near 70° Fah. Now the natural internal warmth of 
the body is very nearly 100° Fah., regardless of the heat of the sur- 
rounding air; and the personal comfort which proceeds from air at 
70°, is found to be accompanied by an actual loss of heat from the 
skin, which is cooled with constancy and regularity and yet without 
so rapid dispersion of heat as to give the sensation of cold. The 
breath also is inhaled at whatever temperature of air may subsist at 
the place, but is exhaled at all times at 90° or 95°. Hence the occu- 
pants of a room, the air of which has a normal temperature of 70°, will 
impart to it such excess of heat as may be given out from the person 
or breath, and if the temperature is to be kept at the 70° point, some 
means of absorbing or dispersing this heat must be provided. 
[The actual quantity of heat proceeding from the formation of 
carbonic acid given out with the breath each minute, as deduced from 
the careful experiments of Doctor Edward Smith, is sufficient to raise 
the temperature of 30 cubic feet of air from 10° to each minute, 
probably about one-third of this heat is taken up in formation of 
moisture from the lungs and skin.] The exhalations of the breath 
are composed of air partially deprived of oxygen (that is with excess 
of nitrogen), carbonic acid and vapor of water with small quantities 
of organic matter in suspension. This organic matter is recognized 
to be the source of effluvia and also of disease, and the great purpose 
of ventilation is its removal. In whatever condition the organic matter 
escapes from the lungs or exudes from the person and passes off with 10 
Report on the Ventilation of the Hall of Representatives. 
the insensible perspiration, it sours or decomposes very quickly—a few 
minutes only suffice for it to become offensive. It makes the offensive 
odor which is found so marked in the galleries or upper parts of halls 
of audience, especially in those which are inadequately supplied with 
fresh air. The exhaled breath has a temperature of 90° (or a little 
above), but, as it has with it a proportion of six per cent, of carbonic 
acid, which is heavier than the equivalent volume of air (in which it is 
diffused and from which it does not separate), the resulting specific 
gravity of expired air is about four per cent, lighter than that of air 
at 70°. From these heating effects of the person it follows that any 
individual is always surrounded and enveloped in an ascending current 
of air; and this current can be made manifest by experiment and shown 
to have a perceptible velocity notwithstanding the downward direction 
of breath from the nostrils. A little spiral of paper mounted upon 
the end of a knitting needle, or a delicate anemometer (instrument 
for measuring the velocity of currents of air) will answer to show 
this phenomena; and the latter instrument will give the ascending 
velocity over the crown of the head at two to five feet per second. 
If this upward tendency of air derived from the contact with the person and the 
levity of the breath did not exist, it is obvious that no large assembly of people 
could live for an hour on a calm day. The vitiation of the air by the emanations 
from the skin and by the exhaled breath with its carbonic acid would bring this 
about. An army could not form in mass, at a review. M. C. M 
If therefore a system of downward ventilation were installed, which 
should give the least supposable supply of air to each individual in 
the Hall, the descending current of air distributed over the whole 
surface of the room would be in opposition to the natural currents 
produced by the heat of the body. In this way the intermixture of 
foul with fresh air would be perfectly consummated, and as the 
volume of air to be introduced (with a least supply) was found to 
be so much as would affect the entire change of the air in the Hall 
(supposing the change to occur without mixture) in eight or nine 
minutes, and the foul air of exhalation must have risen, until by 
mixture its temperature became that of the room ; and it follows that 
at no time would any person on the floor of the Ilall have a single 
breath of pure air. It is not easy to say how far down in the Hall 
the fresh air, which is supposed to enter at the top, would reach as 
fresh air; but it is probable that it would be partly fouled at once, 
and that the whole nine to ten minutes would be the length of time, Report on the Ventilation of the Hall of Representatives. 
11 
in which the mingling of the exhalations from the person and breath, 
with the fresh air, would take place; during which time the organic 
matter in suspension would be partly decomposed. On the other 
hand, with an upward ventilation the fresh air would be breathed 
by any person, within half of a minute of its time of entry, wTith no 
intermingling of currents, and unmixed with exhaled breath; except 
by diffusion downward, in opposition to the direction of flow. Be- 
sides these considerations of the nature of the air when introduced 
by downward ventilation, over the head of an audience, it must be 
noticed in accordance with previous remarks that to preserve the 
temperature of the room at 70° amongst the audience, the fresh air 
’tself must be somewhat below 70°, and that a downward current 
will not only meet the natural upward one, but produce a positive 
flow in the downward direction, which, however small its velocity, 
as a cold current, would be sure to be perceptible, and could not or 
would not be endured. 
There are other and quite as cogent reasons against the introduc- 
tion of air from above. A prominent one in the Hall of Represen- 
tatives, if it be supposed that the vitiated air be removed through open- 
ings in the floor of the Hall, wrould be the passage of the vitiated air 
from the galleries (sometimes crowded with persons) upon the heads, 
and down amongst the members seated on the floor; or if it be sup- 
posed that it be attempted to remove the vitiated air from the galleries, 
by openings in the gallery floor, there would then be an alarming uncer- 
tainty as to the existence of any ventilation on the floor below. But 
without enumerating more reasons, it is enough to claim the sufficiency 
of those already stated; and to say that an upward, plenum, venti- 
lating system met the views of the writer in 1855, and the adoption 
and approval of General Meigs at that time. After twenty years 
more experience, study and examination at home and abroad, and 
after inspection of the present condition of the ventilation of the 
Hall of Representatives, the writer is the more convinced of the pro- 
priety of the decision then reached. 
[It will be noticed that the question of the merits of a plenum or 
exhaust system of ventilation for the Hall, has not been referred to 
in these remarks, but further on in this report the defects and un- 
suitability of an exhaust system either upwards or downwards will 
be strikingly exhibited.] 12 
Report on the Ventilation of the Ilall of Representatives. 
III. The Hall of Representatives is a room requiring no heating. 
It is enclosed by corridors, which are at all times and seasons heated 
to summer temperature, and upon the east and west sides (or ends) 
these corridors themselves are protected from loss of heat by an ex- 
ternal row of well warmed rooms. The basement below the Hall is 
also warmed, and the iron ceiling above is well protected by a large 
air space, covered by a copper roof, and although some loss of heat 
does occur at the ceiling in cold weather, yet the volume of escaping 
air, which is always a little overheated, is so great that the tempera- 
ture of the roof space is generally up to 60° or 70° in the daytime, 
in the coldest weather, rising to 110° when the gas is lighted. The 
problem is, therefore, how to cool the Hall, and how to deprive the 
air which it contains, of the heat emanating from the occupants at 
any given time. 
For the occupants themselves the problem is still more embarrass- 
ing, for it is how to cool from 500 to 1600 people in the Hall, by 
means of currents of air cooler than the general temperature of the 
room, which currents must be introduced and distributed without pro- 
ducing the sensation of cold by any one of the occupants. There is a 
personal—physical—difficulty involved with the introduction of air 
amongst a crowd, and consequently near to some if not each of its 
number, which demands investigation in this place. 
The sensation of cold from contact with air is not that proceeding 
from its temperature alone, but is affected in some means by the hy- 
grometric condition—and to yet greater extent by the action of a 
current or draft upon the skin. It was stated that in still air [of 
American hygrometric condition] the comfortable temperature was 70°, 
but a current of air upon the person at this temperature is uncom- 
iortably cold from the rapid abstraction of heat. At much higher 
temperatures the sensation of coolness from currents of air is felt. 
One fans himself when the thermometer stands at 100° with a sensa- 
tion of relief. This feeling of cold, from air of high temperature, 
when in motion, proceeds from the rapid removal of the stratum of 
warm and nearly saturated air in contact with the person and its re- 
placement by fresh air, which is not only cooler but which has not yet 
become saturated or charged with moisture by contact with a moist 
surface like that of the skin. In no one of the changes in the three 
forms of matter—solid, liquid and gaseous—is there so much heat 
taken up as in the change from a liquid to a gaseous (or vaporous) Report on the Ventilation of the Hall of Representatives. 
13 
form, and in no other body or substance is so much heat absorbed or 
become latent as in the formation of steam from water, or in other 
words, in the process of evaporation; and the quantity of heat taken 
up by the moisture which a dry air abstracts from the skin is so great, 
that the mere differences of temperature of the air, from that of the 
skin may almost be neglected in the statement; and it is very nearly 
correct to assert that the cool sensation from a breeze in summer, pro- 
ceeds entirely from the evaporation of moisture thereby induced. 
Upon this basis it may be noticed that a current of saturated air 
at 100° would neither remove heat by its contact nor by induced 
evaporation, and consequently would be incapable of producing a cool- 
ing effect, while as the temperature on the dew point should fall, the 
current would become a pleasant one. With a high temperature and 
dry air the cooling effect of a current of air (even at 100°) may be 
very pleasant in the sensation, but will be attended with sun-burning 
(even without exposure to the sun) and blisters will be produced by 
the excessive deprivation of moisture from the cuticle or surface of 
the skin. With 80° of temperature and a high dew point a strong 
breeze is not unpleasant; nor likely to be injurious after the person 
shall have acquired some accustomed habit of body to endure it; but 
at 70° and a low dew point, which is the only possible condition of 
heated air in midwinter, the annoyance of a current of even five feet 
per second and its unhealthiness are positive facts. 
These considerations demand that no decided local currents or 
counter-currents shall be formed, or induced in any portion of the Hall; 
and require a distribution of the supply of air upon, or over the entire 
surface of the floor, so as to produce a uniform and gradual ascent of 
the current, in all parts of the room. The solution of the problem, 
then, is only to be reached when we have successfully introduced 
into the Hall of Representatives 50,000 to 100,000 cubic feet of 
comparatively cool air each minute, amongst and in proximity to 1600 
persons, without its being sensibly felt. 
After much deliberation it was concluded to attempt the supply of 
most of the air for ventilation, from registers, (mouths of entry placed 
in and about the lower floor of the Hall,) and to permit the galleries 
to derive their supply, mainly from the ascending columns from the 
space which they surround. The nearest approach to a uniform dis- 
tribution, would of course have been attained by the perforated floor 
and porous carpet of the House of Lords, England; but the habits of 14 
Hep or t on the Ventilation of the Hall of Representatives. 
our people in use of tobacco put this method out of the question, and 
the same objection attached to numerous small open registers, and the 
best arrangement seemed to be a compromise. The floor of the Hall 
had platforms or wide steps, upon which the seats of the members are 
placed, and which are so constructed as to form semi-circles around 
the Speaker’s Desk (the desk being placed in the middle of one side 
of the Hall) and there were three radial inclined, and two other 
straight passages or aisles, which led from the highest platform to 
the forum, Speaker’s Desk, in front and at the sides of the floor. 
The arrangement of the platforms gave to the three nearest the forum 
a width of four feet nine inches, then a wide one of six feet nine 
inches, following this two others of four feet nine inches, and from 
the last semicircle the floor was carried over level to the angles of 
the room. There were thus seven risers of three inches hiffh each. 
The aisles began with a step of seven inch rise and thus had a very 
gradual descent of fourteen inches to the forum ; and the construc- 
tion gave an end or side riser of varying height where each platform 
joined the aisle. 
For the purpose of avoiding the abuses of horizontal gratings or 
registers, therefore, and yet to preserve the vertical direction of the 
currents of air, these ends risers to the platform (side risers on the 
aisles) were availed of, as the places of entrance of fresh air; and as 
the aisles were but three or four feet in width, the strong horizontal 
currents from the opposite sides, would encounter and neutralize each 
other; the intermingled air would have the desired direction upwards, 
and be so much spread out as a vein of air, as to have a relatively low 
velocity of ascent. This arrangement gave three main radial sheets 
of ascending air in the body of the hall, and another main sheet of 
the same kind along the side upon which the Speaker’s desk is placed. 
Other registers were placed at the base of gallery wall, which were 
screened by covers opening downward; and to provide an ascending 
current in the corners, outside the semicircle of the platforms, large 
floor registers were subsequently inserted in each of them. The coat 
rooms were provided with ventilating (supply) registers at the foot of 
the walls; and some flues in the gallery walls connected to openings 
in the galleries, which were made in the parapet wall in front of the 
passages to the seats, and delivered a considerable volume of fresh air 
to them. But much the greater part of the air was made to enter at 
the floor of the Hall, so that members had the advantage of the first Report on the Ventilation of the Hall of Representatives. 
15 
entry of air into the room. This distribution of the registers pro- 
vided that in no case was a current of air directed against any person 
occupying a seat in the Hall, either on the floor or in the galleries. 
The fan employed was of a type selected by Gen. Meigs after the 
published description of M. Combes (“Aerage des Mines”), but more 
closely resembling a fan made by Jacob Perkins in 1826. It might 
be called an air turbine. [The proportions of the parts and shapes 
of blades, etc., were the subject of a paper read before the Institution 
of Civil Engineers, by the writer of this report, in 1870. More than 100 
such fans are used for ventilation of public buildings in the United States 
at this time.] The diameter of the fan (16 feet) was adopted in order 
to give a slow and easy motion to the engine, which drove it by direct 
connection ; and its width at the periphery was such as would give at 
the required pressure, the required volume of air per minute. The 
superficial area of the width, about the periphery, is 64.31 square 
feet; but the area of peripheral discharge of air, which is to be 
taken normal to the 45° angle blades, is 45.49 square feet; whence 
the least cross section of a frictionless duct to carry away air from 
this fan^should be 45.49 square feet. The duct leading from the fan, 
however, had (I believe) an area of 60 to 65 square feet, and this 
area was preserved until it passed under the Hall floor, where a slight 
gradual enlargement occurred. The total area of all the mouths of 
discharge was 80 square feet, but the apertures of the gratings over 
these mouths, had a total sectional area of not much over 40 square 
feet. The velocity of the flow of air from the tips of the vanes of 
the fan when it was giving 50,000 cubic feet per minute, was 1100 
feet in the same time (or 19 feet per second); and with 100,000 
cubic feet per minute, the velocity was 2200 feet (or 38 feet per 
second). 
It is of course desirable that the current of air in which any per- 
son shall be compelled to remain, shall not be much above 2 feet 
per second, although 5 feet per second is not perceptible when the air 
is in the summer condition of humidity. The velocity of flow through 
the apertures in the gratings was very high (i. e. 40 feet per second 
with summer ventilation of 100,000 cubic feet per minute), but 
within 3 or 4 inches of the apertures, the velocity would fall off 3 or 
4 times, by enlargement or spreading out of the stream of air, while 
the practical result of the opposing currents was to make, at each aisle 16 
Report on the Ventilation of the Hall of Representatives. 
a main ascending sheet of 18 inches to 2 feet in thickness, within 
two feet of the aisle floor. 
It must be remarked that comparatively small importance was 
attached to the procurement of low velocity of emerging air, from 
the apertures of discharge; but that it was regarded as in the highest 
degree essential that the resulting currents beyond the apertures, 
should diffuse into slowly ascending volumes, as nearly as possible, 
uniformly distributed within the room; and above all so as not to 
blow upon any one, and thus the entry of air would be made imper- 
ceptible to the occupants of the Hall. 
The spaces of flooring, between the aisles, received their ventila- 
tion partly by mixture of counter currents, which did not attain 
any sensible rate of speed, and partly by diffusion of gases, 
which does so much to establish the equilibrium of gaseous mixtures 
in the open atmosphere as well as in enclosed rooms. It was seen at 
once on the first session, that any one who should enter the Hall 
somewhat chilled from out of doors in winter, could not acquire 
warmth in the temperature of 70°, with the desirable celerity, and 
that more direct radiant heat was necessary. To meet this require- 
ment, fireplaces were made in the coat rooms under the galleries at 
the earliest convenience. 
The entry and distribution of fresh air having been thus provided, 
the removal of vitiated air was effected as follows: Through the 
action of the fan, a condition of pressure of air (or plenum) was 
maintained, by means of which the air would seek to escape by 
every opening from the Hall outwards; and it will be seen that 
under such circumstances, any large local outlet would tend to induce 
a current of air within the Hall flowing towards it. This tendency 
was resisted, and the proper vertical direction and uniformity of up- 
ward flow of air in the Hall was insured, by the judicious placing of 
numerous small outlets in the iron and glass ceiling. The total super- 
ficial area of these outlets was assayed to be sufficiently restricted to 
effect the distributed discharge, and at the same time sufficiently large 
to give the proper delivery of foul air each instant. The means of 
egress above the ceiling were mainly two sets of louvres at the ridge 
or peak of the roof at each end of the building. [These louvres 
were removed from above the Hall to avoid the possible accident of 
drifting snow or rain upon the iron or glass ceiling.] But a portion Report on the Ventilation of the Hall of Representatives. 
17 
of the air escaped by leakage through the copper covering of the 
roof, which is formed of corrugated copper sheets placed overlapping 
each other; and not soldered, confined or made air-tight at the laps 
or joints. 
The delivery of air at all times was perfectly satisfactory, while 
the great area of discharge reduced the rate of the outflowing cur- 
rent to a very low one, but when measured by the anemometer the 
volume of air which passed, Avas found to correspond fairly with that 
which was impelled by the fan at any given time. It used to be a 
matter of exhibition to show that the escaping air was devoid of 
offensive, almost of noticeable odor, and except when the gas was 
lighted above the ceiling, was not offensive to breathe. 
Ample provision was made to supply steam for vaporization or 
moistening of the air, if a hydrated condition was thought desirable. 
IV. Submitting this general account of the origin and nature of 
the apparatus as it existed in 1858, I will now proceed to state the 
result of the examination made, at your request, into its present con- 
dition and operation, enumerating the changes introduced and the 
final result on -the ventilation of the Hall. 
The boilers and running machinery appear now, after eighteen 
years of service, during which time they have had little repair or 
restoration, to be in excellent order. 
The present engineer reports the boilers to be equal to new ones, 
but such a statement is of course to be qualified, possibly by referring 
to some new ones. The engine and fan are certainly in good working 
condition. The main heating coil has suffered from neglect, which 
occurred some years since. One of the four parts was at some time 
injured by the freezing of water in the lower tubes (which was an 
avoidable accident), and it has been removed. With the limited 
supply of air which it has been feasible to introduce for some years, 
even previous to the accident, the three parts remaining were, and are 
of sufficient heating capacity, if the gap made in the bank of pipes 
by the removal of one part were controlled by shutters, to check the 
entrance and flow of a current of unheated air beyond the coil. As 
the main coil now is, the probability of the discharge into the Hall 
of hot and cold waves is very great. All the regulating shutters 
originally intended for the distribution of air in entering the large 18 
Report on the Ventilation of the Hall of Representatives. 
coil (and indispensable for protection from frost if any part of the 
main coil should have its steam shut off) have been removed. The 
remaining parts of the main coil have many split tubes (which prob- 
ably has been occasioned by frost), and the air now supplied is in 
some measure, if not entirely, hydrated by the leakage of steam and 
water. On the whole, the heating capacity is superabundant for the 
present time and season; but restoration to original condition is 
highly desirable before next winter. The separate pieces of the 
removed part are in one of the vaults, and a large proportion of their 
number are available in the restoration, supposing that no new 
arrangement be eventually considered advisable. 
I explored all the air ducts and passages. In company with the 
present engineer I entered and examined the same—from the inlet of 
the fan—from the fan to the coil—above the coil to and beneath the 
Hall floor—creeping in all directions amongst the passages, and finally 
emerging at the opposite, or southeastern corner of the floor. The 
present condition of these ducts and passages as regards cleanliness 
was all that could be asked for; in one or two places there are some 
piles of bricks and rubbish where some walls have been cut through, 
but there is no appearance of anything likely to be deleterious. 
Near the beginning of the duct, shortly beyond the main coil, 
there exists the remains of a shallow tank or basin, which was formed 
by giving a flooring and sides of sheet lead to a portion of the duct 
itself, at a place where there was an original depression. This is a 
relic, I am told, of an attempt to hydrate or supply moisture to the air 
by vaporizing water. 
It was assumed that the air in passing above and across the 
basin of water would take up as much as would be needful to give 
it the summer condition of humidity. This assumption was based 
upon experience with the scorching currents from an ordinary hot 
air furnace, which if they do not take up enough moisture to estab- 
lish the summer condition in a house, are yet very efficient in the 
evaporation of a proportionately large quantity of water; but in 
this instance it was found by trial (not experiment or reasoning) 
that the cool current of air requisite for ventilation of the Hall; 
when passing with accustomed velocity over the limited surface 
of water, failed to evaporate the expected quantity, and the arrange- 
ment fell into disuse. 
In the bottom of this tank there had been an outlet of 2 or 3 inches Report on the Ventilation of the Hall of Representatives. 
19 
diameter, connecting to the drain, which outlet the engineer reported 
to me as having been found by him unclosed and untrapped. When, 
ever the ventilation of the Hall ceased, this opening might have be- 
come objectionable, and possibly some, not very large, quantity of foul? 
air would escape from it; but at any time when the Hall was occupied 
and the fan supplying air, the current would be in the opposite direc- 
tion, and a small quantity of fresh air would escape from this hole. 
Still the existence of such an opening was a decided neglect on the 
part of a former engineer. 
Much change has been made in the passages themselves ; originally 
they were fireproof passages in solid brick-work, nowhere open to the 
wood-work of the floor, and, no gas or water pipes had been allowed 
to be laid in or even to cross them. [The floor of the Hall was con- 
structed in wood, to prevent the rapid conducting of warmth from 
the feet, which would have been occasioned by a brick or stone floor.] 
The changes in the passages, have made many breakages in the side 
walls and the passages now open in many places, under the wood-work 
of the floor; greatly increasing the risk in event of a fire, as the 
burning floor in such case, would then be supplied with air from 
beneath. 
These changes were incident to two several alterations in arrange- 
ment of the seats for members. The first of these (made in accord- 
ance with the express vote of the House of Representatives) was the 
substitution of sofas in place of chairs, and the removal of the desks, 
for each member ; which was accomplished in this way: The three 
radial aisles in front of the Speaker were dispensed with, and the 
platforms extended over them; the middle portions of the platforms 
in front of the Speaker was furnished with sofas of the same curva- 
tures, which gave seating room for all the members of the House ; 
and at the two ends of the platform, beyond the sofas, and in the 
corners of the Hall, were placed large tables, with chairs, for use of 
those who had occasion to write, or to use papers or documents. This 
arrangement discarded the aisle ventilation, and to replace it and yet 
retain the upward distributed currents of air, a great many small 
circular registers were placed in the floor of the platforms in front of 
the sofas. Much care was taken in the construction of these regis- 
ters. They were so made that nothing could pass through and lodge 
in the air passages, while the tops were free to be lifted, for removal 
of anything dropped into the basin. 20 
Report on the Ventilation of the Hall of Representatives. 
It was found that tobacco dried immediately, by the current of air 
passing through the registers, and emitted neither dust nor effluvia; both 
of which are so offensive from a saturated carpet. Alterations in the 
air-passages under the floor were made at this time to conform to the 
new position of registers ; but their fire-proof character was preserved 
in the change. Although the grouping of the registers did not present 
apparently quite as equal a distribution of entering air as the aisle 
arrangement, yet the ventilation of the Hall (as I am informed) 
continued to be satisfactory. 
This disposition of sofas and tables proved, after three or four 
months’ trial, so objectionable to the members, that the House voted 
for an immediate restoration of the desks and seats, taking a recess 
during the session for the purpose; and the second change gave the 
third, and present arrangement of the desks, seats and floor, together 
with the present method of supplying air to the House. This change 
removed the small registers and relinquished the upward direction of 
the currents of entering air; and the air is now supposed to enter 
mainly at the risers or fronts of the steps of the semi-circular platforms. 
There are now seven semi-circular platforms, narrower than before, 
of four feet four inches width ; which have seven front risers, each of 
four inches height; and upon these risers there exists a continuous 
band of two inches wide, of small apertures; each two inches high by 
one inch wide, and placed one inch apart. These apertures are in front 
of a continuous air-passage under the floor, and are controled by 
numerous registers, so as to be regulated independently for every one 
foot or eighteen inches of length of the riser. The air of course 
emerges as a thin horizontal sheet* from the upper risers and is 
* The adhesion of a current of air to a surface, whether horizontal or otherwise, 
is one of the properties of fluids, liquid or gaseous. If a stream of water be directed 
against a plate it will spread over the same, rolling along, augmenting in width 
from diminution of velocity arising from the fluid friction; the fluid friction 
presenting a resistance in the direction of the impulse; the stream or sheet will 
also increase in width by assuming another direction of flow; but the current will 
not leave the plate until some relation of the force of gravity, or other force, is 
established with the derived impulse of the stream, at the place of separation. 
The tenacity of a current of air to the floor or a wall is remarkable. Sir John 
Leslie, sixty years ago, uses this physical law as an explanation of the changes of 
barometer following the tangential direction of impelled and induced wind currents. 
A strong wind existing upon the surface of the earth will not leave it, but merely 
spread the thickness of its stratum,' each particle endeavoring to preserve its 
uniform velocity and the retardation of volume becoming evident in reduction of 
barometrical height. Report on the Ventilation of the Hall of Representatives. 
21 
directed over the face of the platform below them; traversing the 
platform, the sheet receives an augmentation in thickness from the 
next layer of air which escapes from the next risers, and so on until 
the whole seven platforms are swept over; forming a broad sheet of 
air directed against the back of the legs of those who occupy seats 
upon the platform. 
When it is recognized that the whole area of these outlets at the 
risers is such, that with the proper quantity of air supply, it must pass 
them with a velocity of 20 to 40 feet per second, and at the distance 
of one foot in front of the risers, where the stratum of air may be 
supposed to become four inches (the whole height of the riser) in 
thickness, not less than 5 to 10 feet per second; and also that the air 
must be cool, so cool as to feel cold to the naked hand: then it 
becomes apparent that this ventilation cannot be very comfortable. 
After these strata shall have accumulated and converged as a great 
horizontal current within the circle of the forum, they must of course 
be transformed into one ascending column, in front of, and about the 
Speaker’s desk. Two large circular floor registers, possibly 3 feet 
in diameter, discharging upwards, which were inserted in the upper 
corners of the floor when the first change was made, have been retained 
to the present time. These yield a very large part of the air now 
entering the Hall, as the riser registers are frequently closed off. 
The sensation of cold from the horizontal air currents, was by no 
means an imaginary one—the complaints became general; and after 
one season of endurance, during which the experiment of stopping the 
fan was essayed, with the result of want of air for breathing (as at 
present); with the alternating operation of heating the air until it felt 
comfortably Avarm (95° to 100°)—Avhen the heat of the hall became 
unbearable. After many trials in the alternate ways, it was concluded 
that the defect was in the heating apparatus; and that the cool air 
Avhich Avas so obnoxious, was air that had lost its heat in the passages 
under the floor. A subsidiary heating apparatus was therefore 
devised, and placed under the floor of the hall; Avhere is noAV to be 
found, in some places in the fire-proof Avork and in others, under the 
wooden flooring, a number of groups of cast iron steam radiators (or 
heaters), together Avith all the requisite wrought iron steam and return 
water-pipes; which subsidiary apparatus Avas intended to Avarm the 
air for ventilation so that it should not feel cold! Of course the neAv 
radiators would answer to heat the air (or at least a portion of Avhat 22 
Report on the Ventilation of the Hall of Representatives. 
should have been introduced in cold weather), and if the frosted part 
(one-fourth) of the great coil had at the time when the new system 
was introduced, been then injured or removed; in such case the 
radiators would be available in some measure: but even with these 
suppositions the provisions for controlling the heat were so imperfect, 
that the result in merely warming of air was sure to be unsatisfactory. 
Yet this apparatus must have had considerable use, and must have 
produced some local highly heated currents; as there is evidence, in 
quantities of resin which has roasted from unprotected joists and 
boards of the flooring, that a high heat and small volumes of fresh air, 
have at times co-existed near the radiators. The combination of this 
secondary heating apparatus with the first one, and the complication 
of pipes and appliances of control, must be a great puzzle to each one 
of the successive engineers into whose hands the heating and venti- 
lating of the hall has fallen ; without experience, precedent or instruc- 
tion. In the course of these changes and additions there has been 
placed in the air-passages several lines of pipes connected with the 
heating, besides many other pipes for gas or water supply; but except 
that it is manifestly improper to make such use of the passages, and 
likely to impair the working of the apparatus as a whole, if it had 
been operated according to its original plan, and that there is always 
a strong probability that out of sight passages in common use will 
become places for collection of rubbish (which abuse has not followed), 
it cannot be said that any detrimental results have happened from 
these causes. The impairment of the efficiency of the apparatus, by 
the changes and openings from the passages, is so considerable, that 
the other misuses can be passed by without comment. 
In the original construction it was supposed that the pressure of 
air from the fan (less some regulated but very small difference of not 
over one-sixth the total pressure which would be expended in supply- 
ing the air at the further extremity of the hall), would be kept up 
behind the openings of emergence, and would form the motive power 
to affect the entrance of the air against the resistances of the aper- 
tures of the mouths, and all other resistances to the flow of air, until 
it finally was expelled (vitiated in but a slight degree, from its 
abundance) at the roof. All passages leading to the point of entry 
were ample, with, as before stated, easy curves and smooth sides. 
The existing condition of the air passages, will be appreciated by 
•example of one of the branch entrances which I measured: a line Report on the Ventilation of the Ilall of Representatives. 
23 
of the semi-circular riser openings having, by rough approximation, 
a little under one and a half square feet of total area of apertures (in 
openings of two square inches each), has now an entrance, from one of 
the main aisle ducts, of a half a foot area. This entrance leads at 
right angles from the aisle duct, into a narrow, very rough brick-work 
channel of four or five inches width, by possibly two feet in height. 
Of course the pressure of air or velocity of discharge from this vein 
is wholly inadequate to supply the quantity desired—still it is amply 
large until the horizontal currents are abolished. 
V. After investigating the present modes of introducing fresh air, 
the next step in examination, was into the means provided for escape 
of foul air. The original system has already been described, and 
the effect of the present arrangement for introduction of air at the 
risers of the platforms, in producing a large ascending column of air in 
the vicinity of the Speaker’s chair, has also been stated. This 
ascending column, with even a limited quantity of air supply to .the 
Hall, became a vertical upward current of very high velocity (but, like 
any other ascending current, scarcely perceptible to those within it), 
which, on reaching the ceiling, would spread out as a sheet in search 
of the openings for escape. A portion of the air would pass out, but 
the effect of the horizontal currents of entry on the floor was not 
only to form a blast of their own volume, to concentrate at the 
Speaker’s chair, but also to induce the air above them to take the 
same horizontal direction, and the supply of air for this induced 
current would be furnished or sucked from the upper part of the 
room, whereby a general circulation of the atmosphere in the Hall, 
would become established in a continuous roll, accompanied by de- 
scending currents of perceptible, but not very high velocity along the 
northern gallery and wall. As the iron ceiling of the Hall, when 
the outer temperature is below (say) 50°, is cooler than the air 
within the Hall, the sheet of air in passing across it became cooled, 
and the current of descending cooled air which fell upon the heads 
of the members was objectionable at most times; but in cold weather, 
and on any day when the sun did not warm up the air space over 
the ceiling (at night the gas gave all the heat needful, besides acceler- 
ating the discharge of air), the downward drafts became insupportable. 
[See Appendix B.] 
The existence of these currents was attributed to the effect of tlet 24 
Report on the Ventilation of the Hall of Representatives. 
wind upon the roof, supposed to have been deflected by the Dome on 
the Centre Building, which had been erected about the time of the 
change in the method of introducing the air on the floor; and upon 
the ground of this attributed cause it was decided to make the roof 
above the ceiling so tight, that no wind could enter at it, and to remove 
the foul air positively by means of suction fans. The old system of 
air discharges at the roof was now dispensed with. The openings in 
the walls of the Hall which led to the chambers under the discharge 
louvres, were shut up by close doors; and a plaster lining was formed 
beneath the copper roof, so that it should no longer be porous ; and, 
as the walls which surround the Hall itself are carried up solid to the 
roof (which covers Hall, surrounding corridors and rooms beyond 
them in common); there was formed a comparatively air-tight chamber 
between the ceiling and the roof above it. On the north side of this 
chamber (under the roof) there wTas a passage way which led over to 
the roof space above the connecting building between the old Capitol 
and the South Wing. In each of the four corners of this connecting 
building there existed a flue or shaft, whose original purpose, for two 
of them, was for chimnies for the boilers, while the other two were 
used for gas and water pipe mains, but were nearly vacant places. 
Some changes of pipes, and by dispensing with the use of one of the 
chimney shafts (turning all the boiler flues to one chimney only), 
rendered two of these shafts available, one for the downcast to the 
cellar, where some fans could be placed, and the other for the upcast 
of foul air above the roof. Two suction fans of six or eight feet in 
diameter, with a suitable engine, were placed in the cellar of the con- 
necting building, and completed the apparatus for evacuation of foul 
air from above the ceiling of the Hall. 
The cross area of either one of the foul air shafts, is about 27 
square feet (if the lining of chimney has been removed); w'hich open- 
ing now represents the point of restriction of the ventilation of the 
Hall. When the length of the shafts is considered, the area is 
evidently insufficient for the ventilation of 100,000 cubic feet of air 
per minute. 
But the want of dimensions is by no means the chief defect. It 
has been seen that with present arrangements for entry of air, the 
actual supply has some limit in the endurance of the members exposed 
to drafts; and from the result of a trial by one of the associates in 
this Commission, I am informed that only 15,000 cubic feet of air per Report on the Ventilation of the Hall of Representatives. 
25 
minute was furnished to the Hall through a given point in the main 
duct beyond the fan of supply, while a. contemporaneous observation 
at the suction shafts, gave the volume of air extracted, to have been 
25,000 cubic feet of air per minute. From whence was this surplus 
of 10,000 cubic feet of air per minute derived? Obviously it must 
have leaked in at the doors of the Hall or Galleries. And this fresh 
source of new air in the Hall demands an inquiry into the condition 
of the air which has been thus taken from the corridors. 
I will not attempt to give minutiae of the ventilation and appliances 
for maintaining pure air in that portion of the South Wing outside 
of, and surrounding the Hall itself; but simply will assert that there 
exists, ready for instant use, every facility for the purpose; and that 
scarcely a tradition of its manipulation or working, has come down to 
the persons at present in charge of the apparatus. The regular and 
adequate supply of pure air to rooms and hall-ways is now more 
neglected than even that for the Hall, and the action of the suction 
fans in borrowing 10,000 cubic feet of air per minute was merely an 
act of removal into, or exhausting through the Hall; a volume of 
vitiated air—not only what had been impaired by breath, but also the 
product of gas burning, together with that which came from the 
restaurant and cabinets, all of which exhalations, gases, odors and 
impurities should properly be expelled from the very spot where they 
have originated at once, through the proper discharge ventilating flues, 
which are to be found in every room and place in the building; and 
by no means be allowed to contaminate the air of the Hall. 
This defect of the exhausting system, as exhibited in this case, 
whether in combination with the plenum one or alone by itself, can be 
pronounced radical. No care of manipulation will ever so apportion 
the supply of fresh air that an exhaust fan can be relied upon to 
remove that vitiated in the Hall alone, except by at all times driving 
the plenum fan at such speed as will render the labor of exhaust fan 
unnecessary (always provided that the exhaust fans are not employed 
in sucking air to the cellar, and forcing it to escape from the same, 
through very restricted passages). 
The Committee Rooms’ fan and its air ducts are in working con- 
dition. I was assured that some mould had been permitted to accu- 
mulate in them, but this was, or is, only an evidence of almost complete 26 
Report on the Ventilation of the Hall of Representatives. 
disuse; for with the fan supplying but half its air, they would be kept 
as dry as a gale of wind could dry them. The controlling air valves, 
for regulating and securing proportionate delivery of air in all parts 
of the building, whether near to, or distant from the fan, are displaced, 
and no one possesses the knowledge of how to rearrange them. The 
heating coils are out of order, and the means of regulating the heat 
has been forgotten—even the fact that it is necessary to adjust the 
heat has faded from all recollection. Still, although some restoration 
of apparatus before next season will be desirable, yet the introduction 
of an abundant ventilation could be effected at once, by merely putting 
into use the dormant means at hand. 
It should be admitted, however, when speaking of the exhaust 
apparatus, that one marked and apparently good effect came from the 
suction of air from the Hall. By its agency the great descending 
sheet of air, which before fell upon the gallery and floor, on the side 
in front of the Speaker’s chair, was partly intercepted and drawn out 
by the overhead suction duct, above the gallery ceiling on that side; 
and the great ascending column was probably no longer a vertical one, 
—the colder currents from the ceiling, were the first to be abstracted 
from the room, so that the semblance of relief from the cold wind, 
which was imagined to come from “over the dome of the Capitol and 
enter the roof,” was in some degree a reality to the feelings of those 
who had suffered before from cold drafts upon their heads. 
YI. It is easy to see how the ventilating and heating apparatus of 
the South Wing and Hall of Representatives has come to its present 
condition. 
Since the work was planned and built, many changes of superin- 
tendence have ensued; each new direction brought men to operate it 
to whom the apparatus was novel and strange; few parallel apparatus 
exist; in no other nation or land, except in America, do halls of 
audience, crowded with people, demand ventilation against similar 
diversities of climate, for sessions of six to twenty-four, or even forty- 
eight, hours of continuous occupation. 
Those who have been brought to take each new control, have in no 
case been principals or even assistants in the management of appa- 
ratus of like character. With this ignorance, which required learn- 
ing from the very ground not only how to use, but the time and pur- Report on the Ventilation of the Hall of Representatives. 
27 
pose of use of his apparatus; each new engineer or doorkeeper not 
only could not count upon instruction from his predecessor, but he 
has possibly been often, intentionally misled. 
I can assert positively that the engineers as a class and individually, 
must have been generally competent in their business and following 
as steam engineers and as mechanics. This fact is apparent from the 
condition of the boilers, engines and machinery; for after eighteen 
years’ work, with very little substitution or change, all is in good 
running order. Beyond the engineers’ department, the defects and 
depreciations are the results, rather of want of information than of 
neglect. As before stated, the very knowledge of the functions which 
parts were to subserve has passed away ; even the numbers of the 
rooms ventilated by certain ducts and heated by certain coils, have 
been painted out; and no record remains in the hands of the director 
of ventilation, so that the figures on the doors of the coil chambers 
in the cellar are unavailable as information. Neither the intelligence 
nor the intentions of any of the successive engineers is brought in 
question by these observations. 
The relation of the engineer to the ventilating apparatus, is much 
the same as that of the engineer of a factory, to the spinning and 
weaving department. There may be men of competent knowledge 
and skill, who would direct the latter, while attending to the boiler and 
engine ; but the practice of manufacturing is not to entrust such dis- 
similar duties to one individual. 
VII. There was left in the office of the Capitol Extension, and 
probably still is to be found in the hands of the architect, complete 
plans, embracing every detail of the apparatus. [The voluminous 
character of these plans, especially of detail, and their difference from 
architectural construction, would necessarily tend to make them 
incomprehensible without a key from the original designers.] The 
abrupt departure of Gen. Meigs, and the complete absorption of the 
control of the apparatus into the hands of others, have necessarily 
prevented the architect from acquiring much knowledge of the system 
or mode of operation, especially as the responsibility for result did 
not in any way rest upon him; and any interference or assumption of 
authority would almost certainly have been resented. 
It cannot be claimed that the original apparatus was perfect in 
design, or beyond improvement or amendment, but it can be averred 28 
Report on the Ventilation of the Hall of Representatives. 
that, with judicious employment of the appliances furnished; it ivas 
possible to introduce that given quantity of fresh air, which is the 
requisite for healthy ventilation, amongst the throng of people in the 
Hall, and into the several committee rooms and corridors, with the 
least occasion for complaint from drafts. 
Since the completion of the apparatus, during the past eighteen 
years, the writer is not aware that any startling or essential improve- 
ment in the system, or its parts have been devised or applied. The 
most valuable modification in detail has been the one for controlling 
the temperature of the air by admixture of heated and natural cur- 
rents, by registers which cannot be closed off, but only tempered to 
suit the requirement for heat in the room. This was first used at the 
Capitol Extension in conjunction with the last coil put in in 1858 ; 
but has been generally adopted for all buildings heated by currents 
of air, where the plan of the building has been suitably arranged with 
flues from the foundation. The arrangement presents no advantage 
except that it relieves the engineer of a charge and responsibility, to 
control the heat of the entering air, to such degree that the occupant 
of a room will at all times desire the register for supply of air to be 
wTide open [a charge long since forgotten at the South Wing of the 
Capitol]. 
More recently (within two years past) statements of the attainment 
of large success in ventilating halls of audience in England, under 
the patent of Mr. Martin Tobin, have been published in many 
engineering and scientific journals. An examination of Mr. Tobin’s 
patent shows that he claims broadly the introduction of air in a verti- 
cal direction and permitting the ventilation to occur solely by diffu- 
sion.* The methods adopted appear to be numerous standing inlet 
pipes, five feet or so in height, placed all over a room, which dis- 
charge freely upward.—The result is stated to be eminently satisfac- 
tory.—The method is substantially, that first employed in the Hall, 
only that the pipes were avoided in our case. Mr. Tobin’s practice 
must be quite unsightly, and would not meet favor except as a last 
resort in the Hall of Representatives. 
* There was a previous arrangement for distribution of air around the room, by 
means of a continuous opening at the top of a high (5 or 6 feet) wainscot; whereby 
a current of air was introduced imperceptibly into a crowded court, the substitu- 
tion of fresh air, in the middle of the room, being supposed to occur by diffusion. 
This example 'was referred to, at the time of planning the ventilation of the Hall. Report on the Ventilation of the Hall of Representatives. 
29 
VIII. The success of the most perfect ventilating apparatus lies 
in the manipulation. Many defects may be covered by intelligent 
direction and watchful care; but no perfection of system or detail 
will overcome ignorance or negligence on the part of the operators. 
The measure of success of a ventilating apparatus is found in an 
absence of thought of its very existence, by those subject to its influ- 
ence. This standard of excellence was at one time attained and sup- 
ported, and for the first two or three years of occupation of the building 
no comment or remark as to the ventilation was made; and the result 
of any endeavor to elicit opinions from members, generally led to an 
assertion that they knew nothing about it, and could give no opinion 
on its merits. This condition of mind on the part of the members 
should be restored. 
The course to be recommended by the commission should have full 
consideration, and I could not, from my two visits of a few hours 
each, undertake to suggest any instant or radical action. 
The arrangement of the desks and seats for members must be 
accepted as fixed, and there must be a new disposition of registers to 
meet it. 
If it shall be decided that the whole volume of air cannot be intro- 
duced in imperceptible currents amongst the members, or that the pres- 
ence of numerous registers will be open to serious objections, it may 
well be considered as to how to introduce air for the Galleries inde- 
pendently. I must state that this alternative was considered by Gen. 
Meigs 20 years since; but the fascinating idea of introduction of all, or 
most all, the fresh air amongst the members was the ground for decid- 
ing against an independent ventilation for the Galleries. It will, 
however, be found that the arrangement of air ducts under the Coat 
Rooms was planned with a view to dividing the stream of air between 
the Floor and Galleries, and that there exists over the Coat Rooms a 
space suited to hold distributing air pipes of the desired sizes. 
This two-fold system would possess an advantage in the winter 
season. Those who occupy the Floor need and require a drawing- 
room heat, while the occupants of the Galleries are clothed with 
heavy garments ; and their dresses are really uncomfortable Avhen the 
temperature rises above 65°, and oppressive at 7-° to 75°; which 
latter temperature is as low as the Galleries can now be kept with a 
temperature of 70°, below on the Floor. 
I will not pursue these considerations further. They are subjects 30 
Report on the Ventilation of the Hall of Representatives. 
for deliberation rather than of report at this time. The past and 
present of the apparatus are facts which I have stated as briefly as I 
could; the future requires discussion, and the conclusion I cannot 
anticipate. [See Appendix C.] 
This paper which I now present to the Commission has been 
examined by Gen. Meigs, and while it is to be accepted as my own 
individual opinions and views, yet I am able to say that he confirms 
the facts and statements, as substantially agreeing to his recollections 
of them APPENDIXES. 
APPENDIX A.* 
THE QUANTITY OF AIR SUPPLY TO THE HALL—ACTION OF FAN 
AND CONSIDERATION OF PASSAGES. 
I have not been able to find amongst the notes in my possession, 
any record of experiments, as to velocity of currents of air produced, 
or of tbe quantities of air delivered at any time, by the fan for the 
Hall of Representatives. There must be some record of these 
amongst the papers in the office of the Capitol Extension, if they 
now exist, as my recollection extends to several especial observations 
by deputies, as well as by myself. There was imported by the Capitol 
Extension, a Neumann Anemometer (such as is described in Peclet, 
“Traits de Chaleur”), and another much less sensitive was made by 
Wurdemann. Both of these instruments were re-adjusted, and their 
constants ascertained, by placing them in motion in a still room, on the 
end of an arm of fifteen feet radius, which was swung at constant 
speed of rotation about an axis; and they were further tested, by as 
careful comparative observations with each other, and with a water 
column pressure gauge in currents of wind, as we could make. The 
“King” pressure gauge, which multiplies the height of column of 
water pressure, by giving motion to a delicately balanced hand on a 
dial plate by a cord, which passes over a small barrel on the axis of 
the hand, from the float, was not known in 1858-9; but one of these, 
which was made under my instructions without knowledge of King’s 
contrivance, was sent to Washington in 1862; when its use corrobo- 
rated within practical limits, the correctness of the original water 
column observations; and also showed a reasonable correspondence of 
indication of pressure, when opposed to currents of air in the main 
ducts, with the velocities as given by the anemometer. 
The anemometer observations were at all times taken in the duct 
near the fan, either at the entrance of the air to the mouth, or behind 
the fan, at some point where the duct -was well defined in shape; re- 
peated observations in different places in the surface of cross section, 
were selected with a view to obtain the mean rate of flow at that sec- 
* See page 7. 32 
Report on the Ventilation of the Hall of Representatives. 
tion ; the anemometer being attached to a light staff which permitted 
the observer to be removed from obstructing the section. There were 
concurrent observations taken at times in the Hall by the anemometer; 
but the rapid, almost instantaneous, diffusion of the emerging cur- 
rents (excepting always when they are upon, or along some surface, to 
wdiich they can adhere), vitiated all attempts to estimate quantities in 
this way, and the experiments were only useful in exhibiting effects at 
certain distances from the openings. 
The phenomena of the flow of air through a pierced grating can be 
readily understood. If we suppose a grating of one inch square 
openings and of four-tenths of an inch wide bars, so as to be one half 
space and one half solid, and of considerable extent of surface, it 
will be seen that a current of air will, within a very close distance, 
probably two-tenths of an inch (one half the width of a bar) lose half 
its velocity and become a uniform one; were the bars as wide as the 
openings, so that the total surface of openings would be one-fourth 
that of the entire grating, on this supposition of one inch square 
openings; at a half inch from the surface, the current wrould be uni- 
form, and have but one-fourth the velocity of emergence. With the 
bars any other width, the same rule will hold good until some extreme 
limit of distance is reached. Openings two feet apart, regularly spread, 
on the floor of the Hall, would unquestionably verge into one great 
ascending current within a foot from the floor. 
As the ducts were of brickwork, without connections or breaks 
leading to any other channels, and without possibility of leakage; 
it wTas certain that any volume of air which passed a given 
point in them, must enter and go through the Hall; for the 
purpose of ascertaining the volume supplied to the Hall, there- 
fore, it was deemed sufficient to rely upon measurements taken at 
the entrance from the fan. Some experiments made with the Senate 
Fan, at different seasons of the year, of which I find notes amongst 
my papers, will answer to show the performance of the House Fan as 
originally operated. The Senate Fan is only 14 feet in diameter, 
while that of the House is 16 feet, but the former is 1*4 feet wide at 
the tips while the latter is 1’28 feet. The difference of dimension 
arose from the restricted area of the ducts for the Hall, which de- 
manded extra pressure to supply them, and consequently the Hall 
Fan was made 16 feet in diameter, in this wray securing a desired Appendixes. 
33 
speed for the engine, with a higher velocity for the tips of the blades. 
As the volume of air emitted by the fan would have increased beyond 
the requirement for the air ducts if the width of the tips (at the peri- 
phery) had been augmented in proportion to the diameter, a reduced 
dimension was adopted, so that not only the same pressures, but also 
nearly the same volume of air will proceed from either the 14 feet or 
the 16 feet fans when run with the same linear velocity of tips of 
blades; while with the same angular velocities the pressures will vary 
as the square, and the volumes in simple proportion, of the diameter. 
The following is extracted from rough notes in my possession : 
TABLE. 
Senate Fan—14 Feet in Diameter by 1-4 Feet Width at 
Periphery. 
Numb, of 
Pressure at 
Tempera- 
Velocity of 
Volume of Air 
Date of Experi- 
Rev. per 
the Fan, in. 
ture Exter- 
Air in the furnished to the 
ment. 
minute. 
of water col.* 
nal Air. 
Ducts.f 
Chamber per min. 
80 
5-16th 
40.052 to 44.764J 
June 14, 1858... 
80 
5-16th 
67° 
1241 
48.400 
June 14, 1858... 
100 
7-16th 
U 
1596 
62.240 
Jan’y 10, 1859... 
50 
3-16th 
41.116$ 
* Referred to the air in the engine-room, which corresponded to the external air, 
very nearly, the intermediate pressure between inlet and outlet side of Fan was 
uniformly double these figures. 
-j- The area of duct at point of observation was 39 square feet. 
j This was apparently a continued observation of some hours, during which the 
Fan was kept at 80 revolutions per minute. 
§ Some careful observations of velocity of ingress of air at the several mouths of 
entry into the Chamber made concurrently with the duct observation accounted for 
about 33,000 cubic feet of air as entering at the time—the deficiency of 8,000 feet 
was, of course, what was diffused beyond the surfaces of estimate. The large 
quantity of air moved for the small rate of speed of the Fan and small apparent 
pressure can be attributed to the ascensive power of the column of warm air in 
the building, as it was cold at the time.—My record does not giye external tem- 
perature. 
The tabular results of these trials with the Fan for supply of air 
to the Senate Chamber, were in accordance with others made with 
that for the Hall, as well as with those for the Committee Rooms, at 
the same time; and using these by comparison as data, I can assert 
the former supply of air to the Hall, to have been from 50,000 to 
100,000 cubic feet of air per minute, as required. The indications of 
total pressure, at the Senate Fan, was from 3-16ths to 7-16ths of an 34 
Report on the Ventilation of the Hall of Representatives. 
inch; and as a large part of the air for the Chamber was supplied in 
the galleries (the floor having too limited an area to furnish it), the 
length of ducts, their crookedness and obstructions were quite as great 
as those of the Hall; from which it can be inferred that it was not an 
improbable assumption, that six-tenths of an inch pressure from the 
Hall Fan would certainly give impulse to, and supply the allotted 
quantity of 100,000 cubic feet. 
The flow of currents of air through a plate, when they emerge from 
a chamber where the air is at rest, follows the same laws as the flow 
of liquids, and the orifice is taken as subject to a co-efficient of con- 
traction of area (= 0-7 about) in applying the general formula (cor- 
v2 
rections for expansion, etc., being neglected), — — h h„. 
2<y 1 2 
O 
To transform hx — h2 of air into pounds per square-foot, it is only 
necessary to divide by the number of cubic feet of air to the pound, 
at some assumed or stated temperature, [13-25 cubic feet at 70° Fah. 
(barometer 30")—which is near enough as the limits of practical accu- 
racy in this case], and this can be further reduced to water column 
pressure in inches by dividing by 5-2 lbs.—or the weight of an inch 
deep of water on a square foot (at 52° Fah). 
This formula applies to orifices of all sizes, within large limits of di- 
mension, as the ratio of contraction due to the internal flow of liquids, 
(coming from the consideration of least resistance to particle move- 
ment) is the same for openings of all sizes, when the plate is supposed 
to have infinite extension. But it does not apply to the emission of 
air from apertures, as they are to be seen in the Hall, for in these the 
air comes to the apertures with full velocity (in place of being quies- 
cent air under pressure); and while the air must encounter some re- 
sistance of contraction of vein, the co-efficient of contraction is alto- 
gether modified, becoming zero if the mouth of the aperture is merely 
the termination of a channel or pipe. It can only be said that the 
total pressure must represent the flow through the most restricted 
openings—all the duct or passage frictions—all the fan frictions—and, 
in addition to this—must be summed the pressure of plenum in the 
Hall. It would be feasible to obtain a series of pressure indications 
at any point in the air passages, which would, or could, be made to 
indicate the relative speed of the fan below, and also the quantity of 
air it was moving; but it could only be done by comparison of obser- 
vations, and adapted to the given locality for indication; and the ex- Appendixes. 
35 
hibition of the performances would not follow any simple relation of 
pressure to volume, as the volume changed. 
Much thought was wasted in the attempt to devise a set of instru- 
ments of indication and communication; with the final conclusion that 
the instruments would either become so elaborate as to be incompre- 
hensible, or if simple would possess the value of the fair—cloudy— 
storm—of the barometer; the temperate—summer-heat—blood-heat— 
of the thermometer ; or the rain—fine—of the hygrometer. The ad- 
vantages of mechanically directed or performed manipulations, are the 
certainty of repetitions of accomplishment, but unfortunately this is 
dependent upon some uniformity of condition, which must be antici- 
pated. And, again, the establishment of a healthy atmostphere in the 
Hall of Representatives is so intermingled with the preservation of the 
comfort of the individual members, that no rules will ever render the 
climate of Washington amenable to meet the contingencies; and the 
adoption of standards, which do not admit of great latitude in dis- 
cretion, by those in charge of the ventilation, will inevitably, lead to 
contention and disagreement. 
It was concluded that intelligence and watchfulness were essentials 
both for the officials of the Hall, and for those of the Engineer De- 
partment—and accord between them must be maintained. 
APPENDIX B.* 
HEAT OF THE ROOF SPACE OVER CEILING, AND ITS EFFECTS UPON 
CURRENTS IN THE HALL. 
The loss of heat, by the air in the roof space over the ceiling at 
times during the day in cold weather, must have been very great; and 
unless the ventilation were actively kept up, so as to ensure an up- 
ward, outward flow in all the interstices of the iron ceiling, a current 
of cold air following down the under side of the sheet covering of the 
roof, to the eaves, or walls enclosing the Hall, and then spreading 
over a part of the iron ceiling, with a strong tendency to escape down- 
wards, into the Hall itself, might and would be found. 
Nearly 18,000 square feet of surface of sheet glass and copper 
(allowing for the corrugation) have an intermediate temperature 
* See page 23. Report on the Ventilation of the Hall of Representatives. 
36 
between the internal and external air; when, if we suppose the 
internal temperature to be 70° and the external to be zero, the sur- 
face of the roof would become 35°, and in case of a high wTind, 
which would abstract heat much more rapidly than the gentle currents 
of the interior, even 30° or 25° may have been reached; but the 
abstraction of heat from the internal air would bring its temperature 
below 70°, and a consequent fall of that of the envelope would ensue, 
so that finally, for excessive estimate, the surface of cooling may be 
assumed at not over 25°. This assumption will give the cooling effect 
of each square foot of roof, upon the three cubic feet of air (to the 
foot of surface, supposed for coldest weather ventilation of 50,000 
cubic feet, which leaves the Hall per minute at 70°), as that which can 
be computed to reduce the air from 70° to 50° (very nearly); and 
the computation exhibits an apparent probability in its amount. If, 
combined with this refrigeration of the expelled air, a small amount 
of leakage of very cold air at the joints of the copper roof sheets is 
presumed, a still lower temperature would exist at the sides of the 
roof space, so that the entering of a cold current into the Hall could 
only be prevented by a uniform and perfectly distributed pressure of 
air outwards at all the apertures of efflux. [The lighting of gas 
above the ceiling would at once increase the temperature of the space, 
above that of the Hall below. At the season of the year, and at 
the time of day when the coldest weather is likely to happen, the gas 
will generally be lighted. This may be the reason why cold currents 
in the Hall, were not noticeable for the first three or four years.] 
When the change of method of introducing of air on the Floor 
both restricted and prevented the entrance of the proper quantity of 
air, the refrigeration of the roof space would be carried to a yet 
lower temperature, whilst the opposing out-flowing current would 
lose their strength: and as the new arrangement provided a roll 
of air, the tendency of the cold air to fall into the Hall, would be not 
only unopposed but be induced. 
The plastering of the inside of the copper roof was, under the cir- 
cumstances, a very proper and justifiable proceeding, and I am not 
prepared to say but that it might have been the proper thing to do 
regardless of any other changes in the method of ventilation. 
This explanation is, I think, enough to account for the cold air 
which was supposed to have fallen from over the Dome. [Still there 
may be a real current at times from that cause, but if there is—a fact Appendixes. 
37 
which can be detected by trial with smoke on windy days—should it 
be found that downward drafts do exist from this or any other cause— 
the remedy will be some low mouths or towers of discharge, of large 
superficial areas (not less than 100 square feet for the two), shielded 
by cowls, so made as to take advantage of winds from any direction 
in ensuring the delivery of foul air—always trusting to the plenum 
for controlling it.] 
The same line of argument which has been followed here in showing 
the effect of air on the external roof surface, at low temperature, 
with, however, an opposite result upon ventilation of the Hall, can 
be applied to the effect of air at high temperature, and also to the 
effect of the heat from the rays of the sun (the latter, of course, 
being much the more important agent of the two). Whenever the 
covering of the roof is at higher temperature than that of the roof 
space over the ceiling, a sheet or film of heated air will follow up the 
under side of the sheets, and tend to escape at the peak; and if the 
air needed for this purpose, is freely supplied from the Hall below, 
there will be little addition to the heat of the roof space, as air will 
not mingle downwards, and is of itself an almost perfect non-con- 
ductor of heat. The removal of foul air from the Hall, with much 
uniformity, will be accelerated by the action of heat. 
There is another question involved with the temperature of the roof 
space at times, which does not admit of so ready solution as that of 
the abstraction of heat from the roof surface by external influences. 
The lighting of the Hall by gas burners above the roof calls for a large 
combustion of gas. About 5500 cubic feet of gas each hour is burned 
whenever the Hall is lighted; calling for 1900 cubic feet of air per 
minute for combustion only, and generating heat enough each minute, 
to raise the temperature of 50,000 cubic feet of air, from 70° to over 
125°, (if no loss of heat at the roof or ceiling occurs.) The tempera- 
ture of the gases of combustion, allowing a double volume of air for 
dilution, and supposing one-half the heat to be radiant, or emitted 
from a flame of gas light, is very great (1300° Fah.), while the abso- 
lute temperature of the flame is certainly above 5200° ; and the radi- 
ation of heat from these lights is very perceptible, even to those who 
occupy seats 30 feet beloAv; and especially noticeable in summer, 
when the increment of heat, above (say 85° or 90°), becomes oppressive. 
No means of alleviating this effect of radiant heat, or of reducing the 
quantity of heat which accompanies a given quantity of gas burning, 38 
Report on the Ventilation of the Hall of Representatives. 
when the gas is of given quality, has yet been found. But the great 
object of my calling attention to the gas burning at all, is to have 
kept in mind, that whatever scheme of ventilation of the Hall may 
be essayed, the provision of air for the gas burning, and the ventila- 
tion of the roof space must be fully considered. 
Common coal gas has the following constituents per hundred parts : Hydrogen, 
Hj, 44 to 48 ; marsh gas, CH4, 34 to 38 ; olefiant gas, C2H4, and other hydro car- 
bons, etc., 6 to 8 ; carbonic oxide, CO, 5 to 7 ; carbonic acid, C02, 1 to 3; air, N20, 
1 to 3 ; aqueous vapor, H20, (saturation at 40° to 60°,) 1 to 2. The specific gravity 
of coal gas is about 0-430, which makes the volume of a pound of gas at 70° equal 
to 31-4 cubic feet (neglecting fractions, too small to be of consequence in this esti- 
mate) = 0-0318 lbs. per cubic foot, Taking an average of the constituents of coal 
gas, they can be reduced to 53 parts of hydrogen, 34 parts of carbon and 6 parts 
of carbonic oxide, which are combustible ; leaving 5 parts of non-combustible sub- 
stances. From these data, the heat given out by complete combustion can be cal- 
culated—hydrogen gas will evolve in its chemical change to vapor of water (in- 
cluding the latent heat of the vapor) 62,000 units of heat, while carbon is becom- 
ing carbonic acid, evolves 14,500 units, and carbonic oxide, in changing to the same 
form, evolves 4,400 units—with the following results: 
Combustibles. 
Oxygen re- 
quired. 
Air required 
to supply 
oxygen. 
Air required 
to effect com- Units of heat per 
plete combus- lb. of combus- 
tion. tible. 
Units of heat, total 
evolved. 
Product. 
h2o 
54 
432 
1,944 
3,888 62,000 = 
3,348,000 
H20 - 486 
c 
35 
93 
420 
840 14,500 = 
507,500 \ 
C02 = 142 
CO 
6 
8 
36 
72 4,400 = 
26,400 ; 
Totals 
, 95 
533 
2,400 
4,800 
3,881,900 
628 
Deduct latent heat of 486 lbs. vapor @ 1000°, 
486,000 
Combustion of 100 Pounds of Coal Gas. 
Total units of heat from 100 lbs. coal gas (95 com- 
bustible -f- 5 of non-combustible) 3,395,900 
Of this quantity, of 34,000 units of heat per pound of coal gas, it does not seem 
to be an improper assumption, tjjat one-half will be dispersed as radiant heat, and 
the other will be communicated to the gases of combustion, and deseminated by 
convection and intermixture with the surrounding air. The limited base from 
which the flame of a gas burner emerges, as compared to the magnitude of the 
flame or burning surface, prevents the loss or expenditure of radiant heat upon the 
fuel (which again imparts its heat to air in contact before burning), and thus re- 
duces the convected heat to its least quantity. This leaves the convected heat from 
one pound of coal gas, as equal to 17,000 units ; and preserving the assumption, of 
the accompaniment of the air for combustion by one volume of air in addition, it 
will be found by computation based on the specific heats of, vapor of water = 0-475, 
carbonic acid = 0-217, nitrogen = 0-245, and air = 0-233; that the specific heat 
of the melange equals 0-263, and the temperature of the gases of combustion (49 
pounds), arising from the absorption of 17,000 units, will be 1,300°. 
Again if we suppose a burner of 4| cubic feet of gas per hour, which is equal to 
0-C0239 pounds of gas each minute, we find the dispersion of 40-05 units of heat by Appendixes. 
39 
convection ; and the same quantity of heat by radiation, in the same minute’s time. 
At this rate, the 1,228 burners over the ceiling of the Hall of Representatives, will 
consume 5,526 cubic feet of gas per hour, and give out 49,181 units of heat each 
minute by convection. If the quantity of air passing away from the Hall is accepted 
at 50,000 cubic feet, also per minute, its weight (at 70°) is 3,700 pounds, and with 
the specific heat of 0-238, there will proceed 880 units of heat for each single 
degree of elevation of temperature; whence, in dissipating the 17,000 heat units, 
an'increment of 56° will attend the intermixture of the gases of combustion with 
the vitiated air; bringing the temperature of the foul air escaping from the roof 
space to 126°; or higher, if the air from the Hall is above 70°. 
The radiant heat emitted from the burner would be expended upon the surround- 
ing objects, which will either absorb or transmit it (in part) ; and the absorbed heat 
will be finally dissipated by convection to currents of air in contact with the bodies 
of absorption. A portion of the radiant heat will be transmitted through the glass 
(about 40 per cent, of what is emitted against it), to the room below, where it will 
be necessary to cool the air of ventilation correspondingly; bur the most of the 
radiant heat will be imparted to the metal, and other surfaces of the roof space ; 
where it would seem that eventually the heat would accumulate, until nearly the 
whole quantity of heat produced by the gas burning, radiant and otherwise, would 
have to be taken up. This would call for an increment of temperature of about 
110°; giving 180° as the temperature of the foul air emerging from the roof. 
In point of fact, it must be said, that the highest heat recollected by the writer, as 
having been observed in the roof space at any time, was only 115°—but that temper- 
ature is high enough to make the means for controlling the flow of foul air from gas 
burners the subject for serious consideration. 
It may be well to give, as a final comprehensive statement, the fact that the 1,228 
burners of 4£ cubic feet of gas per hour, will burn 5,526 cubic feet of gas in this 
time, or 176 pounds of gas; and each pound of gas will produce about 3J times as 
much heat, as is given from the burning of a pound of coal, upon an ordinary 
boiler grate. From this it appears that the heat produced above the ceiling of the 
Hall by the gas lighting, is that which would be generated by the burning of 600 
lbs. of coal per hour on a grate of about 50 to 60 square feet of surface. 
This question of gas burning, makes it proper that I should call 
attention to a disuse of one of the regulating provisions for supply 
of gas,' which disuse, has been very injurious in its effects on the ven- 
tilation. There was originally in the line of main gas pipes, in the 
place now occupied by the suction fans, a gas governor, which con- 
trolled the flow of gas so as to preserve a uniform pressure in the 
building and to prevent increase of pressure, either when the great. 
Hall system was extinguished as a whole, or when any change of 
pressure was made at the gas works, in forcing the supply of the city. 
This governor may be yet in existence, but out of order; but it w’as 
in working condition for six or eight years. In 1866 (I think) it was 
found, by the writer, to the complete surprise of all the persons then 
employed at the Capitol, and it was then discovered to have controlled 40 
Report on the Ventilation of the Hall of Representatives. 
automatically for eight years—unrecollected and untouched, in con- 
stant motion every day and almost every hour of the day—the admis- 
sion of gas to the building, so that a blow or flare of gas had been an 
unknown occurrence. 
At the present time the broken and smoked shades, the free dis- 
charge of gas where a burner had blown out, and the consequent 
smell of gas which pervades the building and is sucked into the Hall, 
are the consequences of the neglect or removal of this valuable re- 
gulator. 
APPENDIX C.* 
IMMEDIATE MEASURES TO BE TAKEN TO IMPROVE THE VENTILATION 
OF THE HALL. 
The measures to be recommended for the procurement of immediate 
relief are first, and above all, the restoration of the method of intro- 
duction of air into the Hall with positive upward direction, and with 
general distribution of the mouths of discharge. The riser openings 
must be closed altogether, or else their entire length must be shielded 
by a deflecting shield which shall remove the tendency to establish the 
great converging, horizontal, floor current, now so offensive, when any 
considerable volume of air is supplied. A shield of wood or metal— 
the same height as the step, four inches—placed two inches in front 
of the present riser, would merely advance the edge of the steps (with 
the thickness of the shield), two and a half or three inches, and could 
be made so as not to be noticeable as a novelty or makeshift; and the 
total superfices of these openings for admission would then be 144 
square feet, so that if half the air needed for maximum ventilation 
passed through these openings, the velocity of efflux at them would be 
about ten feet per second; which current at one foot elevation would 
not exceed two foot per second, and at the height where it could 
come into bodily contact with any one sitting in a chair near by, not 
over one foot per second. The registers behind the present apertures 
in the risers would answer to control the distribution. Having in this 
way made it feasible to supply air in the Hall; the conduction of air 
beneath the floor to these lines of entry should be made certain, by 
some enlargements and roundings off of the passages, so that there 
* See page 30. Appendixes. 
41 
should be no restrictions of area, or angles, to prevent the adequate 
flow along them. It may be well to insert two more large registers, 
in each of the triangular corners formed by the semicircle of the 
platform and the angles of the room ; and these registers, together 
with the ones now in these triangles should have air-tight brick ducts of 
supply, leading from the main air passages, with proper curves to pre- 
vent eddies and loss of momentum of the current. 
All openings from the air passages to the flooring should be at once 
closed and the passages made once more suitable for the conduction of 
the air to definitive points. This course is rendered imperative (if for 
no other necessity) for the purpose of getting the proper quantity of 
air at the further (or eastern) end of the Hall; the introduction of 
air being at the western end. It will be found, by examination of the 
building, that the large marble corridor in the basement, has an iron 
ceiling which comes up close under the Hall above; and the plans of 
the air passages will show that on, or across, the line of the aisle in front 
of the speaker, the requisite sectional area was obtained only by using 
the channels formed in the iron box architraves of the lower corridor. 
Consequently the main air passages from the fan to this point must 
be intact, or else the leakage or escape of air from uncontrolled outlets 
will so far relieve the pressure, as to affect the supply on the eastern end, 
and be especially disastrous upon that supply, when the volume of air 
introduced at a given time is not large. The adjustment of the equality 
of supply of air at the two ends of the Hall, under these circum- 
stances, was provided for by registers placed below the floor in the 
sides of the air passages; which registers regulated the quantity en- 
tering the flues leading to the gratings in the Hall; and as these flues 
were disproportionately large they became in fact chambers of equili- 
brium, in which the air existed at that definitive excess of pressure 
which would overcome the exit through the grating at a constant velo- 
city, regardless of the differences of pressure in the main passages. 
The registers were at first adjusted with great care by the ballistic 
effect of the emerging currents on paper pendulums of uniform size 
and weight of load, so that the velocity of efflux for 60,000 feet per 
minute was practically equal at all points of the Hall. At this time 
no regulation of the distribution remains. * * * * 
The Suction Fans can be dispensed with, with the greatest advantage, 
as soon as suitable openings can be made in the roof for the egress of 
air. I have not the areas of the original louvre openings at hand, but my 42 
Report on the Ventilation of the Hall of Representatives. 
recollection leads me to the opinion that they were not so large, as to 
relieve the roof chamber of such pressure, as would ensure the outflow of 
air at the joints of the corrugated copper. The plastering on the inside 
of the roof now prevents any escape of air in this way, and the open- 
ings should be made large enough to admit a nearly free discharge of 
the spent air. Under no practical condition can the down-take and 
up-cast shafts be made to pass the quantity of air which should go 
through the Hall in summer, because of want of area. The velocity 
of passage of this air pre-supposes such relative pressure that at any 
time when the supply fan does not furnish enough air, the abstrac- 
tion of air from the rest of the building is inevitable. There is no 
necessity of the air in the roof space being further treated than 
'permitted to escape. 
No mechanical objection can be made to the suction fans for the 
Hall. In fact they are in principle, and in construction of parts 
acting upon the air, essentially similar to those for supply of air. 
The chief and apparent differences arises from the entrance of air at 
both sides of the suction fans, while it is taken in to the large supply 
fan from one side only; and in the use of iron cases in lieu of a brick 
chamber for the fans to run in ; but the suction fans are small in effec- 
tive section, and a higher velocity of current and greater expenditure 
of power is demanded to pass the same volume of air. 
The apparatus for the ventilation of the Committee Rooms, outside 
of the Hall, should be instantly put into performance of its work. 
This alone will help the whole ventilation beyond expression. The 
specific operations for this purpose would involve, if each point was 
discussed and set forth intelligently to the Commission, quite as much 
writing as is given in this report in the Hall alone; I will only say, 
therefore, that the apparatus exists comparatively in good order and 
unchanged, so that direction is nearly all that is requisite. 
The Restaurant has grown from a place to lunch, to the magnitude 
of a hotel; and the ventilating flues from the crypt, where the cooking 
is done, have been appropriated as a chimney, for an extra fire (I 
think that was done as long ago as 1860), and no means of taking 
away the odors of cooking now exist. These odors are not very 
offensive to hungry people when fresh, but they are the accompani- 
ment of organic matter which is probably in combination with vapor 
of water, and the latter (with its organic matter), is absorbed by any 
hygroscopic substance near it. The organic matter does not decom- Appendixes. 
43 
pose rapidly, but is retained in its place of absorption for a long time, 
gradually changing and emitting a characteristic foetid smell which 
becomes permanent in the walls of unventilated kitchens. The kitchen 
and the rooms of the crypt near it, can now be mildly stigmatized as 
vile; and the odor permeates beyond, into the basement rooms above, 
and is sucked into the Hall. It would be very easy to connect a large 
flue from the top of the arched ceilings of the kitchen to the upcast 
foul air shaft, and remove the vapor of the cooking—of course it may be 
needful to provide air supplies to the kitchen to prevent the ventilating 
flue from overpowering the chimnies—but in some way this nuisance 
should be corrected. 
The cabinets and water closets in the basement are also open to 
grave complaint. They have proper and adequate flues for the escape 
of air. No entering flues lead to them. It was intended that they 
should derive their fresh air from the corridors and vestibules, which 
were supposed to be supplied by air under pressure seeking to escape, 
so that the currents would always set into the doorways. The infre- 
quent and partial working of Committee Room Fan, and the relinquish- 
ment of the ventilation, has allowed the air to stagnate in these cabi- 
nets until they have become offensive, and their odor at some distance 
beyond the places themselves is perceptible. 
The remedy here is that suggested before.—Put the ventilating ap- 
paratus to work at its best effect. 
APPENDIX D. 
THE FULL CONSIDERATION OF THE SUBJECT OF VENTILATION AND 
WARMING. 
This report has been restricted to the consideration of the subject 
of warming and ventilation in two ways: first, no general discussion 
has been attempted; and second, even the application of principles 
or methods to the Hall ventilation has been limited to those with 
regard to which, it seemed to the writer that some doubt existed either 
in the minds of the Commission, or of other persons who have examined 
into the subject with insufficient knowledge of the physical or struc- 
tural conditions. 
Thus no comment has been made upon the quantity of air requisite. 
It has been assumed that the volumes of fresh air proposed to be sup- 44 
Report on the Ventilation of the Hall of Representatives. 
plied per individual and per minute would meet the approbation of 
the Commission, and no facts or arguments on this point were deemed 
necessary. To any one who desires to study primary questions, a 
simple reference to a standard authority; Dr. Edmund A. Parkes’ 
“Practical Hygiene,’' 1866, will be more instructive than a brief 
treatise of recapitulation of his data on these pages. 
Dr. Parkes’ treatise on the nature of air, its several impurities from 
all causes, their removal or dilution into excessive volumes of purer 
air, is exceedingly thorough and ample; yet he does not give proper 
weight to the effect of difference of humid condition—a change which 
makes our Washington temperature of comfort 10° higher than that 
accepted by him, while the midwinter temperature of comfort in 
Montreal is 20° higher at least—and he fails to consider in any way 
the methods of supply of the designated quantities. 
To live comfortably every man in the United States should have an 
income of $600 per year, is much like the assertion, that 50 to 60 cubic 
feet of air should be supplied to each individual in a room each minute. 
Dr. Morrill Wyman’s “Treatise on Ventilation,’’ 1846, contains 
some practical details as applied to American climate. Other works, 
the best of them German or French, are filled with constructive details 
applicable to our own use. E. Peclet, “ Traits de la Chaleur,” 1860-3, 
being the most extensive and thorough in all regards; but the practice 
of the mechanism is always likely to be precedent to the record, and 
in ventilation and heating, what is undescribed, is by no means an 
unimportant part of what is known; while the American practice, of 
Joseph Nason, is almost entirely unpublished. 
The respective merits of the different systems (as they are improperly 
called) of ventilation has not been discussed in my report with any- 
thing like the fullness, with which they would be presented in a general 
treatise on the subject. Any examination into the nature or directions 
of currents, or of the process of diffusion which accompanies upward 
or downward, horizontal or vertical, influx or efflux, or even much 
allusion to them in words has been avoided; and my inquiries and 
statements, have been confined to the consideration of the especial 
example of the Hall of Representatives. It must not, therefore, be 
assumed, that while I have asserted that an ascending currerlt is the 
sole possible course compatible to the conditions in the Hall, that 
under other conditions other proceedings in ventilation, may not only 
be possible, but may also be advisable. Thus it must be recognized Appendixes. 
45 
that where occupied rooms, in which the cubical space per inhabitant 
is relatively large (600 to 1200 cubic feet) to that of a hall of audience 
(300 cubic feet, accompanied by much disproportion of height in the 
Hall of Representatives) are heated as well as ventilated by currents 
of air at low temperatures, the only way to secure the desirable 
warmth on the floor, is to abstract the colder air which has chilled on 
the windows or walls, from or near the floor itself. And this statement 
applies, to either the method of heating by currents of warm air 
entering the room by flues (leading from heating surfaces placed in 
the lower stories) or to the heating by direct radiating surfaces (so 
called) in the rooms themselves, where the fresh air is derived either 
by leaks at the cracks of doors or windows, or more rarely, by 
openings for admission specially provided near the heating surfaces. 
Those who have had experience in the warming of storehouses, offices 
or workshops (or even of habitable rooms) by low pressure steam, or 
by hot water at low temperature; and have attained a competent 
knowledge of the requirements to give the temperature of comfort (the 
procurement of which sensation having been all that was deemed essen- 
tial by most people); are apt to carry their information beyond the 
conditions of their own practice, and to assume that the same methods 
and appliances which gave satisfactory results in their experience will 
prove equally successful in all other cases, including, of course, halls 
of audience of all kinds, amongst which the Hall of Representatives 
can be classed only as a case of special qualifications. 
The questions of cooling of air in summer, of production of a 
warmer condition in winter, together with the numerous applications 
of medical, physical or mechanical laws involved, are out of place in 
this paper. They might require consideration if it were undertaken 
to answer or reply to the numerous propositions which have been 
made in reports offered for the consideration of previous committees 
of Congress ; but, with the conviction that the Commission desire only 
to be told how, and for what reason, it was proposed to supply an 
abundance of fresh air at the several seasons—warmed to the tempera- 
ture of comfort in winter, and in quantity to the volume of comfort (as 
near as possible to out of doors in the shade) in summer; I have not fol- 
lowed the proposition to change the seasons into a perpetual spring time. 
The truth is, all our heating and ventilating appliances are a com- 
promise of conditions—a truth extending beyond all mechanical 
operations to the phenomena of nature itself. ERRATUM. 
REPORT ON THE VENTILATION OF THE HALL OF 
REPRESENTATIVES, 
U. S. CAPITOL, WASHINGTON, 
TO PROF. JOS. HENRY, COL. T. LINCOLN CASEY, HR. J. S. BILLINGS, 
EDW. CLARK, ESQ., F. SCHUMANN, ESQ., 
COMMISSION OF INQUIRY, ETC. 
By ROBERT BRIGGS, C. E. 
Substitute for pages 37, 38, 39 and 40, Appendix B. the new pages seut 
with this. 
This correction of the note on the heating power of gas involves no changes 
in the bod)- of the text except on page 37, line 27. for 1900 read 1124, and 
same page, line 42, for 5200° read 4760°, which are now corrected in the 
proper places. 
KOBT. BRIGGS, C. E. 
220 South 4th St., 
Philadelphia, Nov. 28, 1877. 
Please remove pages 37, 38, 39 and 40 of the pamphlet sent you in 1870. 
and insert the above.