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XV . 'Experiments and Obfervations relating to Air and Water . 
By the Rev. Jofeph Priefiley, LL.D. F.R. 8 , 
Read February 24, 1785. 
TV VER fmce the difcovery of the diminution of refpirable 
* air in thofe proceffes which are generally called phlogijlic 5 
it has been a great objedt with philofophers to find what be- 
comes of the air which difappears in them. Among others, I 
have made and published a variety of experiments with that 
view; but though by this means fome farther progrefs was 
made in the philofophy of air, and confequently our know- 
ledge of the principles, or conflituent parts, of natural fub» 
fiances was extended, I did not by any means fucceed to my 
fatisfadlion with refpedt to the immediate objedt of my re- 
fearches. Others, however, were mpre fuccefsful, and their 
fuccefs has at length enabled me to refume my experiments 
with more advantage ; by which means I have been led both to 
confirm their conclufions, and, by diverfifying the experi- 
ments, to throw confiderable light upon various other chemical 
proceffes. The refu.lt of thefe obfervations I fhall lay before 
the Society, with as much brevity and diflindtnefs as I can. 
In the experiments of which I fhall now give an account, 
1 was principally guided by a view to the opinions which have 
lately been advanced by Mr. Cavendish, Mr. Watt, and 
M. Lavoisier. Mr. Cavendish was of opinion, that when 
air is decompofed, water only is produced ; arid Mr. Watt 
concluded , 
