Thomson's Sj/sttm of Chemistry. 145 



tion, it requires twice its volume of oxygen gas, and produces 

 exactly its own volume of carbonic acid*." But one volume of 

 defiant gas requires three volumes of oxygen, and two volumes 

 of hydrogen require one of oxygen, constituting four volumes of 

 oxygen to three volumes of the gases, mixed in his proportion ; 

 instead of four to two, as his own statement requires. So that 

 '• a mixture of one volume olefiant gas and two volumes hydro- 

 gen would not possess the chemical properties of carburetted 

 hydrogen." Again, when we turn to the Annals of Philosophy, 

 for November, 1820, where this criticism lies stretched at full 

 length, we find him floundering in a quagmire of figures, and em- 

 ploying, as usual, algebraic symbols, to perplex one of the 

 plainest cases of arithmetic. " Suppose now," says he, " 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 hydro- 

 gen gas." Here we have two-thirds of a volume of hydrogen, 

 which, like the rogues in buckram, suddenly become three times 

 that proportion in his system, or two whole volumes. But, 

 waiving this contradiction, let us examine his elaborate criticism 

 in the Annals. The specific gravity of a gaseous mixture is 

 found at once, by dividing the sum of the weights by the sum of 

 the volumes. Therefore, when one volume of olefiant gas, and 

 two-thirds of a volume of hydrogen are mixed, their joint spe- 

 cific gravity will become, 



0.9722 +(0-0694 x ^') - qgII 



Let us now see, how the Doctor goes to work, to solve 

 the same problem, and what result he obtains. " Let A zz 

 volume of olefiant gas ; a =: specific gravity of olefiant gas ; 

 let B =: volume of hydrogen gas ; b rr specific gravity of hy- 

 drogen gas ; X = specific gravity of a mixture of A -f B of the 

 two gases ; it is easy to demonstrate from the common principles 

 of pneumatics, that 



Bh + Aa 



X ^ 



A + B 



" In the present case, A = 1 ; a = 0.9722 



B = 0.66 ; h = 0.0G94 



" Consequently ^ _ 0.68 x 0.0694 + 0.9722 _ q ggj^g 



1.6G 

 " But this specific gravity is quite different from 0.5555, the 

 true specific gravity of carburetted hydrogen +." Inimitable 



* Vol. I. p. V.'i.O. 



t ^'tnaU of I'hUoiophy, November 1820, p. 381, 38i!. 

 Vox.. XL L 



