vni THE BURNING OF INFLAMMABLE GASES 157 



hydrogen, and the other half to the charcoal. This leading 

 fact afforded a clue to its constitution." 



" The properties of carburetted hydrogen are : 



" It is unfit for respiration and for the support of combus- 

 tion. 



" Its specific gravity when pure, from my experience, is 

 very near o'6. 



" Water absorbs ^V of its bulk of this gas." (New System, 

 1810, II. 445-446.) 



Olefiant gas, by contrast, had a specific gravity 0-9 relatively 

 to air, and was absorbed by water to the extent of \ of its 

 bulk. 



Composition of marsh gas. Dalton showed that of the 

 two volumes of oxygen required for the complete combustion 

 of marsh gas, one was required to burn the carbon, giving 

 rise to an equal volume of carbonic anhydride, whilst the 

 other was used for the combustion of the hydrogen. Marsh 

 gas, therefore, contained, like olefiant gas, twice its volume 

 of hydrogen ; but the carbon was only sufficient to produce 

 an equal volume (instead of two volumes) of carbonic 

 anhydride or of carbonic oxide. This view of the composi- 

 tion of the gas was confirmed by sparking it, when the 

 carbon was deposited and two volumes of hydrogen were 

 set free. Dalton writes : 



" If 100 measures of carburetted hydrogen be put to up- 

 wards of 200 of oxygen, and fired over mercury, the result 

 will be a diminution of near 200 measures, and the residuary 

 100 measures will be found to be carbonic acid." 



" When a portion of carburetted hydrogen gas is electri- 

 fied for some time, it increases in volume, in the end almost 

 exactly doubling itself; at the same time a quantity of 

 charcoal is deposited. The whole of the gas is then found 

 to be pure hydrogen" (ibid. p. 447). 



When exploded with an equal volume of oxygen the carbon 

 was burnt to carbonic oxide and half the hydrogen was 



