OR, PLAIN TEACHING. 



75 



carries with it small particles of 

 carbon, and these, becoming in- 

 tensely heated throughout the 

 body of the flame, glow and emit 

 light. The soot deposited upon 

 chimneys, and over jets of gas, 

 consists of small particles of car- 

 bon which escape unconsumed. 

 The matter driven off from coals 

 is gas, combined with other mat- 

 ters, and because it consists of a 

 mixture of carbon and hydrogen 

 it is called carburetted Tiydrogen. 



Take a tobacco-pipe, 15, and 

 nearly fill the bowl, 16, with bits 



of coal, cover it with clay, then 

 put the bowl in the fire ; in a short 

 time tar and smoke will issue from 

 the item; when these have passed 



away, the escaping hydrogen may 

 be burnt from the point, where it 

 will produce a jet of luminous 

 flame, 17. This shows that the 

 i hydrogen of coals may be separated 

 I from the carbon thereof by heating 

 j the mass to a high temperature. 

 Gas, by which our houses and 

 streets are illuminated, is made 

 upon this principle, but by a 

 more complicated method, in con- 

 sequence of the necessity of sepa- 

 rating tar, sulphur, and other 

 substances contained in coals, 

 which would otherwise render gas 

 offensive, and impair the light. 



Coals are put into either iron 

 or clay retorts, A A, which are 

 set in furnaces in. such a manner 

 that they may be heated through- 

 out uniformly. 



** The retort being heated .to a red-heat, the 

 charge of coal, about 200 lbs., is quickly 

 shovelled in, and immediately gives oft dense 



