Experiments on the different Kinds of'Coal. 285 



different degrees of a high temperature, is of some importance, 

 even in an economical point of view. From the same oil may 

 be obtained for lighting, either a larger quantity of gas of bad 

 quality, or a smaller quantity of incomparably better gas, ac- 

 cording as the carbonization is effected by means of a weaker or 

 stronger heat. 



If the principal object of the operation were to obtain char- 

 coal, it would be necessary to employ at first as low a heat as 

 possible, and not to make it rise till near the end, in order to 

 lose only the smallest possible quantity of charcoal in the gase- 

 ous combinations and fluids which are formed. This also shews 

 that the products of dry distillation, with reference to the same 

 organic body, must present differences as well of quantity as of 

 kind, according as the temperatures employed have been diffe- 

 rent. This is a circumstance which, in a great number of cases, 

 would require to be more taken into consideration than it has 

 hitherto been. 



It is known that the products of the distillation of unaltered 

 and perfectly dry vegetable fibres in the air, are an empyreu ma- 

 tic acid, water, oil, a very small quantity of alcoholic substance, 

 and a gaseous mixture, consisting of carbonic acid gas, carbonic 

 oxide gas, carburetted hydrogen gas, and olefiant gas. The 

 mutual relation of all these combinations, and the quantity of 

 carbonaceous residuum, depend upon the temperature. 



If shavings of wood be exposed for a long time to a tempera- 

 ture which does not rise above 120° of Reaumur, a period ar- 

 rives when there is no longer observed any change of weight. 

 In this operation, wood dried at the temperature of the air, but 

 not at the temperature of boiling water, loses from QQ to 69 per 

 cent, of its weight. Dried at the latter temperature, the wood 

 would lose at the most from 5Q to 59- Thus the residuum, 

 which perfectly resembles common wood-charcoal, only that it 

 presents a somewhat duller aspect, weighs from 41 to 44 per 

 cent, of the real quantity of wood which has been employed, al- 

 lowance being made for moisture. This carbonaceous substance 

 is what M. de Rumford has named the frame-work, or skeleton, 

 of plants. That philosopher considered it as a pure charcoal, 

 which he imagined to exist in equal quantity in all plants. But 

 M. Karstcn concludes, from his own researches, that the pre-. 



