242 Dr. J. W. Draper's Remarks on the 



others to which I will presently allude, some chemists have 

 altogether rejected the hypothesis of gaseous action, perhaps 

 on very insufficient grounds. It is therefore desirable that 

 the subject should be more extensively investigated, and these 

 objections set aside. No one can do this more ably than 

 yourself. 



If a soap-bubble be expanded with hydrogen gas, in an at- 

 mosphere of common air, and then be suddenly burst, so as 

 to accomplish an instantaneous diffusion and intermixture, at 

 the moment at which this occurs there is an expansion, which 

 is apparently of a thermal kind, inasmuch as the gaseous 

 mixture, in a short space of time, recedes to its original 

 volume. One hundred measures of hydrogen and four hun- 

 dred of atmospheric air occupy, on the moment of being 

 mixed in this way, considerably more space than five hun- 

 dred measures. Does not this indicate that the particles of 

 these gases occupy, when their temperature has fallen to the 

 original degree, a less space than the sum of their volumes 

 before mixing ? Is it not a phaenomenon of the same kind 

 as that observed on mixing alcohol and water, when there is 

 a thermal disturbance, followed by a penetration of dimen- 

 sions? In other words, does not this experiment give indi- 

 cations of proof, that certain gases, on being simply mixed, 

 exist in a condensed state ? 



This result is readily observed on mixing hydrogen with 

 atmospheric air, and also with nitrogen gas. I detected it 

 some years ago, but have not yet been able to show it in the 

 case of other gases. If it be really due to a condensation 

 taking place, it is an experiment of no ordinary importance ; 

 especially if it should be found that the same occurs on 

 mixing oxygen with nitrogen. It would indicate to us one 

 of those " other causes" which keep up the integrity of the 

 constitution of the atmosphere. 



One of the most powerful arguments brought forward in 

 support of the hypothesis of gaseous action, is founded on the 

 experiments of Professor Graham ; it is, that the law which 

 regulates the flow of gases into a vacuum, is precisely the same 

 as that which regulates their flow into each other: is this 

 however strictly the case? 



Professor Graham has shown*, that when hydrogen gas, car- 

 bonic acid, &c. are separated from atmospheric air by a thin 

 screen of stucco, they diffuse themselves according to the law of 

 the square roots of their density. One volume of air, for ex- 

 ample, replaces 0*8091 of carbonic acid gas ; the gas therefore 

 on that side of the screen where the carbonic acid was placed, 



[* See L. and E. Phil. Mag. vol. ii. p. 175 ; vol. iv. p. 321,] 



