184 NON-METALS AND THEIR COMBINATIONS. 



The gas mixture thus obtained, known as water-gas, may be used for heating 

 purposes directly, but has to be mixed with hydrocarbons when used as an 

 illuminating agent, for reasons which will be pointed out below when consider- 

 ing the nature of flames. 



Carbonyl chloride, COC1 2 . This is formed when a mixture of carbon 

 monoxide and chlorine is exposed to sunlight, and, hence, is also known as 

 phosgene. Commercially it is made by passing a mixture of the two gases over 

 animal charcoal, which acts as a catalytic agent. Carbonyl chloride is gas- 

 eous above 8 C., has a suffocating odor, and dissolves readily in benzene. 

 Water decomposes it at once into carbonic and hydrochloric acids, COC1 2 + 

 2H 2 O = H 2 C0 3 H- 2HC1. It is used in making certain synthetic organic 

 compounds.. 



Compounds of carbon and hydrogen. There are no other two 

 elements which are capable of forming so large a number of different 

 combinations as are carbon and hydrogen. Several hundred of these 

 hydrocarbons are known, and their consideration belongs to the 

 domain of organic chemistry. 



Two of these hydrocarbons, however, may be briefly mentioned, 

 as they are of importance in the consideration of common flames. 

 These compounds are: methane (marsh-gas, fire-damp), CH 4 ; and 

 efhene (olefiant gas), C 2 H 4 . 



Both compounds are colorless, almost odorless gases, and both are 

 products of the destructive distillation of organic substances. De- 

 structive distillation is the heating of non-volatile organic substances 

 in such a manner that the oxygen of the atmospheric air has no access, 

 and to such an extent that the molecules of the organic matter are 

 split up into simpler compounds. Among the gaseous products 

 formed by this operation, more or less of the two hydrocarbons 

 mentioned above is found. 



Marsh-gas is formed frequently by the decomposition of organic 

 matter in the presence of moisture (leaves, etc., in swamps) ; and dur- 

 ing the formation of coal in the interior of the earth the gas often 

 gives rise to explosion in coal mines. During these explosions of the 

 methane (mixed with air and other gases), called fire-damp by the 

 miners, carbon is converted into carbon dioxide, which the miners 

 speak of as choke-damp, or after-damp. 



Flame is gas in the act of combustion. Of combustible gases, 

 have been mentioned : hydrogen, carbon monoxide, marsh-gas, and 

 olefiant gas. These four gases are actually those which are found 

 chiefly in any of the common flames produced by the combustion o? 

 organic matter, such as paper, wood, oil, wax, or illuminating gas itself 



These gases are generated by destructive distillation, the heat being 



