Account of a neiu Eudiometer. 1 1 7 



Spheric air, as transparency, elasticity, and a power of great 

 expansion on being exposed to an increase of teinpcraturc, 

 they were, with very few exceptions, till lately, confounded 

 either with common air, or not even suspected to exist. 



When to these considerations we add the facility with 

 which sonae products, especially the gaseous, arc evolved, in 

 circumstances under which, in the present state of our know- 

 ledge, we should hardly look for them ; the .power they pos- 

 sess of decomposing each other, and by an interchange and 

 new arrangement of principles, of producing compounds pos- 

 sessing properties akogether different from those of the in- 

 gredients supposed to be present; and the facilities which 

 every new detection of unsuspected principles affords towards 

 the discovery of others, and consequently the composition 

 or analysis of bodies befoi-e held to be simple, it will not 

 appear a matter of surprise that the subject of eudiomctry 

 should have obtained a considerable degree of attention from 

 modern philosophers. 



This would be an improper place to enumerate all that 

 has been done or proposed by different men of eminence 

 towards the production of something like a perfect system 

 on this important subject ; yet some allusion to their labours 

 appears to be indispensable, and will be the means of pre- 

 venting some circumlocution in our further progress. 



Hales* appears to be the first who observed absorption to 

 take place in common air, on mixing it with air obtained 

 from a mixture of Walton pyrites and spirits o*^ nitre; and 

 that in this process from being clear they became " a reddish 

 turbid fume." 



Dr. Priestley, as he informs us in his " Observations on 

 different Kiilds of Air f," was much struck with this expe- 

 riment, but never expected to have the satisfaction of seeing 

 this remarkable appearance, supposing it to be peculiar to 

 the Walton pyrites ; till encouraged by a suggestion of'Mr. 

 Cavendish, that probably the red appearance of the mixture 

 depended upon the spirits of nitre only, he tried solutions 

 of the different metals in that acid, and, catching the air 



*•- Statical lissays, vol. i. p. 2'_'1; vol. ii. p. 2!;0. 

 t Phil. Trans, for 1772, p. L'lO. 



1 1 '^ which 



