vin THE BURNING OF INFLAMMABLE GASES 143 



reduces the water, liberating hydrogen from it, and is itself 

 converted into carbonic oxide (loc. tit., p. 52). This gas is 

 now prepared by blowing steam into fuel that has been 

 made hot by an air-blast, and is known as WATER GAS ; it 

 consists mainly of hydrogen, carbonic oxide, and carbonic 

 anhydride. As the steam cools the fuel, water-gas can 

 only be prepared alternately with producer gas ; a mixture 

 prepared by blowing in steam and air together is known as 



SEMI-WATER GAS. 



B. QUANTITATIVE EXPERIMENTS ON THE COMPOSITION 

 OF THE OXIDES OF CARBON. 



Composition by volume. It was noticed by Priestley and 

 by Lavoisier that charcoal burnt in air or oxygen does not 

 cause any change of volume, until the fixed air produced is 

 absorbed by water, by lime-water, or by an alkali. Oxygen 

 thus suffers no change of volume when it combines with 

 carbon to form carbonic anhydride ; at the same time 

 carbonic anhydride is shown to contain its own volume of 

 oxygen, thus : 



carbon + oxygen > carbonic anhydride 

 i vol. i vol. 



The composition of carbonic oxide .is less easily deter- 

 mined, because it is necessary to use a pure gas for the 

 analysis. Desormes and Clement found that 100 parts of 

 the gas exploded with about 40 parts of oxygen, and gave 

 about 80 parts of carbonic anhydride. Cruikshank 

 obtained similar numbers for gas prepared by means of 

 charcoal; but gas prepared by means of iron gave 19/20 of 

 its volume of carbonic anhydride when exploded with 

 oxygen. Berthollet (quoted by Gay-Lussac, A.C.R. IV. 

 15) found that 100 parts of the gas combined with 50 parts 

 of oxygen to give 100 parts of carbonic anhydride. From 

 Berthollet's values it follows that carbonic oxide takes up 



