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XII. A new Eudiometer , accompanied with Experiments , e/wa- 
dating its Application. By William Hasledine Pepj/s, Esq . 
Communicated by Charles Hatchett, F R. R. 
Read June 4, 1807. 
The important part which atmospheric air performs, in main- 
taining the principle of life in animals, in combustion of every 
description, the acidification, and oxidation of a great variety 
of substances, and in numerous other processes both of nature 
and art, gives a high degree of interest to every thing calcu- 
lated to extend our knowledge of its nature and properties. 
The evidence furnished by modern chemistry, of the exist- 
ence of many other aeriform substances, increases this interest, 
especially when it is considered that, owing to their possessing 
some of the most, obvious properties of atmospheric air, as 
transparency, elasticity, and a power of great expansion, on 
being exposed to an encrease of temperature, they were with 
very few exceptions till lately, confounded either witn common 
air, or not even suspected to exist. 
When to these considerations, we add the facility with which 
some products, especially the gaseous, are evolved, in circum- 
stances under which in the present state of our knowledge, 
we should hardly look for them ; the power they possess of 
decomposing each other, and by an interchange and new ar- 
rangement of principles, of producing compounds, possessing 
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