t£)2 Description of an Apparatus for the 



tar, with only an equal consumption of oxygen, yields 150 

 measures of carbonic acid. 



5. The aeriform product of coal does not precisely answer 

 to the characters of any one of the combustible gases with 

 which we are acquainted. The first product, however, of 

 the distillation of common pit coal, after being washed with 

 potash, approaches very nearlv in its properties to carbureted 

 hydrogen gas. The gases, which surpass this in specific gra- 

 vity, are mixtures of carbureted hydrogen with defiant gas, 

 and perhaps a small proportion of carbonic oxide. The 

 lighter gases, in addition to carbureted hydrogen, probably 

 contain a variable proportion of hydrogen gas and a small 

 quantity of carbonic oxide. The extreme levity of some of 

 the products, especially of the gas from Mertkyr coal, can- 

 not be explained on any other supposition. 



6. The products of the combustion of a cubic foot of coal 

 gas, of medium quality, viz. of the specific gravity 622, (such 

 as the first products fron Neivcaslle on Tyne coal,) may be 

 stated as follows : 



Grains. 



A cubic foot, at a mean of the barometer and ther- 

 mometer, - - - — - 333*5 



By combustion, it yields 817*3 grains of carbonic 

 acid, the carbon in which may be estimated * 



at - - - - 233-7 



Grains of hydrogen in a cubic foot of coal gas, - 99-8 



But 99*8 grains of hydrogen are equivalent to the satura- 

 tion of 554*9 grains of oxygen, with which they form 654*7 

 grains of water. Hence the oxygen consumed ought from 

 calculation to be 817*3 — 233*7 = 573*6 + 554*9=1128 



And the quantity actually consumed appears by 



experiment to be - - - 1110*3 



Error - - - 17*7 



The difference, in this example, between experiment and 

 calculation is not greater, than, in such delicate processes, 



* Assuming the carbon to be 28-6 grains in 100 grains of carbonic acid, as 

 is satisfactorily proved by the experiments of Messrs. Allen and Pepys. 



may 



