44 MEMOIR OF DR. DALTON, AND 



genous gas ; if more, then some residuary nitrous gas will be 

 found. 



" These facts clearly point out the theory of the process : 

 the elements of oxygen may combine with a certain portion 

 of nitrous gas, or with twice that portion, but with no inter- 

 mediate quantity. In the former case nitric acid is the 

 result, in the latter nitrous acid ; but as both these may be 

 formed at the same time, one part of the oxygen going to one 

 of nitrous gas and another to two, the quantity of nitrous gas 

 absorbed should be variable; from 36 to 72 per cent, for com- 

 mon air. This is the principal cause of that diversity which 

 has so much appeared in the results of chemists on this subject." 



In the paper on the expansion of elastic fluids, he had 

 already, in a plate, shown that he was accustomed to view 

 gases as composed of definite particles, having drawn each 

 with a different form. 



Immediately after this, January 28th, 1803, he read, an 

 inquiry " On the tendency of elastic fluids to diff*usion through 

 each other."* This subject was first begun by Priestley. 

 The memoir which he has written on the transmission of 

 gases through porous vessels, entitled " Experiments re- 

 lating to the seeming conversion of water into air," is 

 certainly one of the most beautiful specimens of investiga- 

 tion that can anywhere be found. He there establishes the 

 fact, that through porous vessels, gases pass one way, vapour 

 of water and other liquids another ; and observed, that the 

 mercury in one experiment had risen 3 J inches above the 

 level on the outside. He afterwards found that what could 

 take place with " air and water, will be done with any two 

 kinds of airs." 



He failed, however, to make the next step, having said 

 that it is probable " that if two kinds of air of very different 

 specific gravities, were put into the same vessel with very 

 great care, they might continue separate," although his 



• Memoirs, Vol. 1., New Series, p. y59. 



