:

nostrils, and I believe he went so far as to declare that it took the direction of a definite mathematical curve. From the experiments of Roscoe, Dr. Wetherell, and others, we learn that the atmosphere, in large rooms occupied by man, is as rich in carbonic acid near the ceiling as at the floor. Those who advocate the system of ventilation by aspiration (or exhausting the foul air) have not always stated this fairly, having cited isolated cases of analyses instead of taking the mean of a great many observations. The first one who attacked this problem fairly was Dr. Wetherell himself, and I cannot do better than to quote him verbatim. "On March 27, 1865, at 11⁄2 P. M., in the laboratory of the Smithsonian Institution, the temperature of which was 69.26° Fahr., a delicate thermometer, held in the hand for several minutes, indicated 95.36° Fahr. Held in the mouth, and observing the degree by the aid of a mirror, it indicated the same temperature. Upon smoking a pipe with a stem of wood six inches long, slowly, with the thermometer also in the mouth, the temperature did not sensibly rise. Having thus obviated a source of error from any supposed heat in the tobacco smoke, I experimented upon the air currents of the breath, both while sitting and standing, following them readily by the aid of the smoke. Before expulsion the smoke was held in the mouth for a short time to insure its temperature to be the same as that of the breath, and the hot pipe was held or placed aside. When the smoke is expelled gently from the nostrils, as in the act of breathing, it proceeds downward a foot or less, and then rises rapidly."

I think this experiment, which any one may easily repeat, should set aside the vicious theory that the heavy carbonic acid in the breath we exhale carries it rapidly and certainly to the floor. The many analyses of air taken from different parts of a large room do not show that its superior specific gravity carries it certainly downward. The carbonic acid probably diffuses itself rapidly with the pure air present, and its direction is affected very much more by natural air currents than by its superior weight. In his experiment the Doctor neglected to note whether or not the windows were open, or whether any currents were induced by the fire, which at that season was burning; and though he demonstrated fairly that the exhalations do not essentially flow downward, I think he has not proved the opposite.

Fig. 1 is a transverse section of the fifth state room on the port side of the Vandalia's ward room, which is opposite a hatch and is near a wind sail. By means of a delicate Casella anemometer I have been enabled to ascertain the direction of the air from the wind sail, and

have indicated it in fig. 1 by arrows. The anemometer used is so sensitive that its vane moves freely in a current of air that will not perceptibly deflect the flame of a candle. The curtain was kept open both at the top and bottom, in order to permit a free circulation of the air, and when the air port was closed there could not be found the slightest current above the berth. On one occasion, when the air port was closed, the observations, which were taken immediately on rising, showed 19.036 parts of carbonic acid in a specimen of air taken from behind the berth, (at A, fig. 1,) while a volume of air from the wind sails of 11,016 cubic feet per hour was flowing through the room, in the path indicated by the arrows. On another occasion, with the air port open, similar observations showed 6.662 parts of carbonic acid while 21,600 cubic feet of air per hour flowed through the room, in the paths indicated by the arrows in fig 2. The analyses for carbonic acid were made by Assistant Surgeon George Arthur, who employed Park's method, while the air currents were measured by the writer.

It is evident from the above experiments that the exhalations should be breathed into the air current, or that we must sleep in a draught if we would breathe pure air. In order to supply an outlet for the vitiated air which accumulates behind the berths, Dr. Arthur proposes an exhaust tube, as shown in fig. 3. With natural ventilation or with a forced blast there can be no doubt that Dr. Arthur's tube would be of great value in exhausting the impure air, and with ventilation by mechanical aspiration this tube would reverse its action and supply the fresh air. From the direction taken by the currents, as delineated in fig. 1, it would appear that Arthur's tube is well located, and also that the exhaust tubes on board the Richmond, which are above and back of the berths, are properly placed, but I think we should not lose sight of the necessit of quickly drying the decks, and I would, therefore, recommend placing the exhaust openings in the floor, and depend on Arthur's tubes as inlets. From the experiments referred to above, made with the air port closed, and again with it open, we have another evidence that the air currents take the direction of least resistance; and in order to uniformly disseminate the pure air, and to insure its reaching every part of the ship, we must remove the impure gases from the points where they are generated, and it is obvious that we must employ some system of aspiration, either natural or artificial.

QUANTITY OF AIR.-Not many years ago it was believed that the quantity of air needed to keep an apartment wholesome was merely equal to the amount exhaled, which is about 12 cubic feet per hour;

but a set of experiments to determine the quantity necessary to dilute the carbonic acid exhaled by the lungs to something near the normal quantity, indicated that 3 cubic feet per minute, or 180 per hour, would be sufficient. Later observers concluded that the necessary amount would be that which would dissolve the aqueous vapor expelled by the lungs and skin, thus preventing the hygrometric condition of the air from rising too far above that of the surrounding atmosphere, and that 5 cubic feet per minute, or 300 per hour, would be sufficient. Assuming that the air admitted upon the berth deck of a ship be mixed by at once diluting the carbonic acid present, we will find it an easy matter to calculate what the volume of that air shall be. Let us take an example from the steam sloop Vandalia, one of our latest ships, and one that is considered to have relatively good ventilation. On the 12th of August, 1879, Assistant Surgeon Geo. Arthur collected a jar of air from the middle of the ward room, and by subsequent analysis (by Park's method,) found it to contain 6.983 parts of carbonic acid in 10,000 parts. At the same date and hour, the writer found the quantity of air (as measured by a Casella anemometer,) admitted into the ward room to be 96,780 cubic feet per hour or 9,678 cubic feet for each of the ten occupants, which is vastly more than is necessary to keep the air at the purity found by Dr. Arthur. Assuming the air supplied by the wind sails to contain 4 parts of CO, per 10,000, which is the normal, we have all the data necessary to ascertain the volume of air essential to keep the air at the above mentioned purity.

Let Q the quantity of air, in cubic feet, to be supplied.

=

Then

10

c the fraction of carbonic acid found in the air of

the

0.0004

And, substituting the numerical value for the letters in the formula, we

have

or

(10x 0.686)-(10x 0.686 × 0.0006983

0.0006983-0.0004

= 22,981,

22,981 10 this calculation by a different method, and, as it has been adopted by Dr. Wetherell and others, it will not be out of place to verify the above results by comparison with Roscoe's method.

= 2,298 cubic feet of air per hour per man. Roscoe made

Let V represent the volume of air free from carbonic acid that would be required, and a the fraction which the impurity of the air (0.04 per cent.) is of the limit of the impurity in the mixture (0.06983 per cent.), and let Q the volume of normal air required. Then Q = V+Va+Va2+Va3× Va*+

Va

(2)

It will be sufficient to calculate the first five terms only of this expression :

0.06983: 99.93017:: 6.86: V = 9,817

or 2,155.4 cubic feet per hour per man, instead of 2,298 as found by formula (1), though it will agree nearer and nearer the farther it is followed. But let us compare the volume of air actually admitted with the quantity essential to preserve the purity mentioned. We find that a Casella anemometer, purchased from respectable dealers in Philadelphia, (Queen & Co.), verified by the U. S. Signal Office in Washington, indicated the enormous quantity of 96,780 cubic feet per hour, or 96,780

(22,981

=) 4.2 times the necessary amount. Had this 96,780

cubic feet of air per hour mingled with and diluted the carbonic acid in its passage through the ward room, Dr. Arthur would have found very much less of that poisonous gas in his analyses. By transposing from formula (1) we can calculate the number of parts of CO, he would have found, viz.