1817.] Azote and Oxygen. 187 
(p. 264) no mention is made of atmospheric air being one of those 
combinations. These last observations plainly suggest the idea of 
simple mixture. 
Soon after Lavoisier’s work the popular Elements of Chemistry 
by Chaptal were published. ‘This author has a section “ on the 
mixture of nitrogen and oxygen gas, or of atmospheric air; ” and 
he seems every where to consider it as a mixture, in the common 
sense of the word. 
- In 1800, Mr. (now Sir Humphry) Davy published his valuable 
researches relating to nitrous oxide, &c. in which the several com- 
pounds of azote and oxygen were ably investigated, the results of 
which we shall have to mention in the sequel. Mr. Davy was in- 
clined to consider atmospheric air as “ the least intimate of the 
combinations of oxygen and nitrogen,” and observes, “ that the 
oxygen and nitrogen of the atmosphere exist in chemical union 
appears almost demonstrable from the following evidences :— 
“J. The equable diffusion of oxygen and nitrogen through 
every part of the atmosphere; which can hardly be supposed to 
depend on any other cause than an affinity between these prin- 
ciples. 
“ 2. The difference between the specific gravity of atmospheric 
air and a mixture of 27 parts oxygen and 73 nitrogen, as found by 
calculation; a difference apparently owing to expansion in conse- 
quence of combination. 
«¢ 3. The conversion of nitrous oxide into nitrous acid, and a 
gas analogous to common air by ignition. 
* 4. The solubility of atmospheric air undecompounded in 
water.” 
I may observe here that the last three evidences, though plausible 
at the time, have since been shown to be without solidity. 
In 1802 my essays on the constitution of mixed gases were pub- 
lished, containing an hypothesis to explain the uniform diffusion of 
‘gases by mechanical means; on this principle the atmosphere was 
of course considered as a mixture, and not a combination of its 
elements. 
Soon after this, Berthollet, in his researches into the laws of 
chemical affinity, announced a new explanation of the phenomena 
of mixed gases. According to this eminent chemist, there are 
two species of affinity; the one strong, the other weak : the strong 
affinity makes bodies combine ; the weak one only serves to diffuse 
them through each other without producing condensation of 
volume ; its effects may be called soludion or dissolution, Of this 
kind, he conceives, is the mutual action of gases that do not com- 
bine, and that it operates just the same upon gases inclined to com- 
bination or not; thus a mixture of carbonic acid and hydrogen is 
subject to this weak or slight affinity just as much as one of oxygen 
and hydrogen. Something similar to this is maintained by Mr, 
Murray in his Elements of Chemistry (1806), and by Dr. Thomson 
in the third edition of his Chemistry (1807). Mr. Gough wrote 
