v THE STUDY OF GASES 71 



capable of being separately exhibited in the form of a 

 permanently elastic vapour, not condensible by cold, to 

 which I give the name of air, any more than the thing that 

 constitutes smell. In fact they knew nothing at all of any 

 air besides common air, and therefore they applied the term 

 to no other substances whatever. 



" Mr. Boyle was, I believe, the first who discovered that 

 what we now call fixed air, and also inflammable air, are 

 really elastic fluids, capable of being exhibited in a state 

 unmixed with common air .... 



" Besides these two kinds of factitious air, that which I 

 call nitrous air obtruded itself upon Dr. Hales ; but even 

 he had no idea of there being more than one kind of air, 

 loaded with different vapours ; and was far from imagining 

 that they differed from one another so very essentially as 

 they are now known to do. And though Mr. Boyle, Dr. 

 Hales, and others, could not but be acquainted with the 

 effluvium of spirit of salt, and also of volatile alkali, they 

 could have no idea that the substance which had those 

 powers was capable of being separated from common air, 

 and of being exhibited free from moisture, in the form 

 of a permanently elastic vapour, to appearance exactly 

 like that which constitutes the common atmosphere .... 



" Even Mr. Cavendish, whose experiments relating to air 

 immediately preceded my own, appears not to have had so 

 much as a suspicion of this kind. For he relates an 

 experiment of his, on the solution of copper in the marine 

 acid, as inexplicable, except on the hypothesis of there being 

 a kind of air that lost its elasticity by the contact of water, 

 which admits of the easiest solution imaginable, on the 

 supposition of the spirit of salt emitting a vapour, which 

 though capable of being confined by quicksilver, and of 

 being by that means exhibited in the form of air, was 

 instantly absorbed by water, which would thereupon become 

 possessed of all the properties of common spirit of salt. 



" In fact, none of the chy mists appear to have had the 

 least idea of its being even possible to separate the acid or 

 alkaline principles from the water with which they are 

 always found combined ; and therefore, though they did 

 suppose them capable of further concentration, they still 



