1S20.] Philosophical Transactions for 1820, Part I. 381 



tion, and that it forms its own volume of carbonic acid gas. 

 From this he deduced its composition, viz. two volumes or atoms 

 of hydrogen and one of carbon. It is to Mr. Dalton then that 

 we are indebted for all the accurate knowledge which we possess 

 of this gas, though he was not its discoverer. 



The only mode of procuring it which I am acquainted with is 

 to collect it from stagnant waters in the way first practised by 

 Dr. Ingenhousz. I have examined it very often from stagnant 

 water in the neighbourhood of Edinburgh, and London, and 

 Glasgow, and have always found it exactly the same. 



Nothing is easier than to demonstrate that carburetted hydro- 

 gen gas is not a mixture of defiant gas and hydrogen gas ; but 

 a true, definite, chemical compound. Its specific gravity, as I 

 have shown in the last number of the Annals of Philosophy is 

 0*5555, and it is a compound of 



2 volumes hydrogen gas ^ , j ■ . i 



1 , •' f u r condensed into one volume. 



1 volume vapour or carbon J 



The true specific gravity of olefiant gas, as may be seen in the 

 paper just referred to, is 0*9722, and it is a compound of 



^ , ^ ^ r ^ u i- condensed into one volume. 



2 volumes vapour oi carbon J 



Suppose now we wish to make a mixture of olefiant gas and 

 hydrogen such that it will require for complete combustion 

 exactly twice its volume of oxygen gas, it is obvious that we 

 have only to mix together one volume of olefiant gas and two- 

 thirds of a volume of hydrogen gas ; for such a mixture would be 

 equivalent to 



2*666 volumes of hydrogen gas 

 2 volumes vapour of carbon 



Oxygen gas. 



Now 2*66 volumes of hydrogen gas require 1*33 volumes 

 2*00 volumes carbon 2*00 



3-3i3 



But 1*66 X 2 = 3-33. Thus it is obvious that such a mixture 

 would just require twice its volume of oxygen gas for complete 

 combustion. Let us see what the specific gravity of such a 

 mixture will be. 



Let A = volume of olefiant gas, a = specific gravity of ole- 

 fiant gas ; let B = volume of hydrogen gas, b = specific 

 gravity of hydrogen gas ; x = specific gravity of a mixture of 

 A + B of the two gases. It is easy to demonstrate from th© 

 common principles of pneumatics that 



