286 M. Karsten's Observations and 



tended skeleton of plants is only an imperfectly decomposed ve- 

 getable fibre, and that it is not at all a pure charcoal. 



In reality, says M. Karsten, vegetable fibres, after the dis- 

 union of their elements, preserve the external form of undecom- 

 posed fibres, and they experience no other change in their form 

 than a diminution of size ; but it is a consequence of the fact 

 which has been mentioned ; it is because the disvmionof the ele- 

 ments of these vegetable fibres, at a temperature of about 120° 

 of Reaumur, cannot be carried beyond a loss of weight which 

 varies from 66 to 69 per cent. There results from this, that, 

 if the temperature be raised above that point, then a new loss o'f 

 weight commences, which, in its turn, remains constant for the 

 new degree, until, at length, at the temperature of incandes- 

 cence, the disunion of the elements of these fibres is completely 

 effected ; and after this no diminution of weight takes place. 



The products of this slow decomposition are very different 

 from those which are obtained by a decomposition effected by a 

 rapidly increased heat. Wood of hornbeam (Carpinus hetur- 

 lus), which, under a rapid carbonization, yields the ordinary 

 products of distilled wood, and furnishes 13.3 per cent, of char- 

 coal, developes, under a slow elevation of tlie temperature, 

 much more water, carburetted hydrogen gas, and carbonic acid 

 gas. It then furnishes 26.1 per cent, of charcoal, that is to say, 

 nearly twice as much as in the case of a rapid carbonization. 

 The decomposition of unaltered vegetable fibres commences, 

 therefore, at a pretty low temperature ; and the reason of this 

 is, that, in' wood-fibres, the quantity of oxygen and hydrogen, 

 as is known by the analyses of MM. Gay Lussac and The- 

 nard, occurs pretty nearly in the relation necessary for the for- 

 mation of water. 



The charcoal obtained from vegetable fibre by means of dry 

 distillation, or by carbonization, appears to vary but little in our 

 common woods. In a synoptical table, the author presents the 

 results of experiments upon twenty-one kinds of unaltered ve- 

 getable fibres, such as oak, beech, hornbeam, birch, pine, lime, 

 straw, fern, reed, and a piece of birch- wood which had served 

 as a prop in a mine for an Imndred years, but was still in good 

 preservation. In all these trials, the matter was employed in 

 the state of shavings, which had been perfectly dried in the open 



