216 On the Determination of the [Sept. 



the tube, KF, into the tube, F G, passes through the wholeof it, 

 and makes its escape by the tube, G I. The part, D E, of the 

 tube through which the gas passes, is long enough to enable the 

 gas during its passage to acquire very nearly the temperature of 

 boiling water. The gas, when it leaves this tube, passes into 

 the calorimeter, L, where it gives out its heat, and then issues 

 out by the tube, N O, which conducts it to the bladder, V'. It 

 fills this bladder, driving the air of the vessel, M', into the 

 reservoir, B', by a tube which plunges to the bottom of the 

 reservoir. 



When all the air has been driven out of the reservoir, B, and 

 water has been substituted in its place, then the bladder, V, is 

 empty, and the vessel, M, full of air from the reservoir B. The 

 bladder, V, is full of hydrogen, and the reservoir, B y , full of 

 air, from the vessel, M'. If we now shut at once the stop-cocks 

 a, c,f, h, and open g, e, d, Z>, and put the gazometer, B', into 

 action; then the air issuing from the gazometer by the stop-cock 

 g, will fill the vessel, M / , press upon the bladder, V, and cause 

 an uniform currentof hydrogen gas to pass through the stop-cock 

 e, into the tube, D E, where it will be heated. It will then pass 

 through the calorimeter, and issuing out by the tube, N O, it 

 will pass through the stop-cock, d, into the bladder, V, will fill it, 

 and drive the air of the vessel, M, into the reservoir, B. Thus 

 matters will be brought to their primitive state, and we may 

 commence the process as at first. With a bladder filled with 

 hydrogen ga6 we may pass an uniform current as long as we 

 please through the calorimeter; and we know, from experience, 

 that, notwithstandingthe continual agitation given to this gas by 

 making it move so frequently through so long a circuit, it does 

 not contain, after having circulated for six hours, three per cent, 

 of impurities.* 



The greatest part of the apparatus which has been described 

 is contained in the same room; but the calorimeter, the ends of 

 the tubes D E, F G, and a part of the tubes G I, N O, are in 

 another room, separated from the first by the door, P Q, which 

 has proper holes in it to allow the tubes to pass. This second 

 room being but seldom opened, the air which it contains, and 

 which surrounds the calorimeter, is seldom agitated, and its 

 temperature scarcely varies. 



* The gas continually agitated in moi-t bladders was always saturated with 

 humidity at the temperature of the bladders. Though we took no precautions 

 to dry it, we do not think that the vapour produced any sensible effects upon 

 our results ; 1st, Because none could be deposited in the calorimeter, which was 

 always a good deal hotter than the bladders. 2d. Because it could oi.ly act as a 

 mixed gas ; and although the vapour of water has twice as great a specific heat as 

 the same volume of air, we aiade our experiments at a temperature too low (48 - 

 Fahrenheit) for it to produce any sensible effect. 



