ATTENDING THE FORMATION OF COAL, &c. 271 



but condensible by great pressure and intense cold, and 

 give much light ; — in the third, the atoms of hydrogen ex- 

 ceed those of the carbon; these are altogether unconden- 

 sible, and give little light (carbon 2, hydrogen 4). When 

 coal and similar organic matters are distilled at a compara- 

 tively low temperature, the carbon has a disposition to pass 

 off with little hydrogen; the liquid hydro-carbons are formed, 

 there is much ta* and little gas, but the gas iarich. As 

 the temperature rises, the liquid hydro-carbon diminishes 

 in quantity, and gaseous hydro-carbon increases; there is 

 more gas and less tar (olefiant gas and volatile hydro-car- 

 bons). The temperature still rising, the gaseous products 

 become richer in hydrogen, and poorer in carbon ; light 

 carburetted hydrogen is formed in abundance; and at 

 length, the temperature becoming still higher, pure hydro- 

 gen is given off, as is always observed in the last hour's 

 distillation in gas- making. 



It is a well-known law of organic chemistry, that the 

 -higher the temperature, and the more advanced the decom- 

 position of organic matter, the simpler are the products. 



When olefiant gas is passed through red-hot tubes, or 

 over red-hot lime or crystal, or, in fact, over any red-hot 

 surface, it deposits a portion of carbon on the red-hot mat- 

 ter in a solid form, and escapes as a mixture of carburetted 

 hydrogen, and hydrogen. The same thing I have proved 

 also of naphtha, C. 12, H. 6, which deposits carbons in like 

 circumstances, and is resolved into simple products. 



The affinity between carbon and hydrogen seems to di- 

 minish with the temperature. 



Is it not probable, that in the distillation of masses of 

 coal, compounds rich in carbon are first formed^ the carbon 

 being in excess of the hydrogen ; as the product rises in 

 temperature, it deposits a portion of its carbon, the atoms 

 of hydrogen become equal, and a rich gas is formed ; but 

 this, getting still hotter, deposits more carbon, the hydrogen 



