Experiments on the different Kinds of Coal 289 



unaltered vegetable fibre. According as fossil wood approaches 

 more or less to the nature of brown coal, it furnishes a greater 

 or less quantity of charcoal ; but, in the carbonization of fossil 

 wood, as well as in that of brown coal, the quantity and kind of 

 the products formed depend upon the degree of the temperature, 

 although, in the species which come nearest to brown coal, the 

 limits are already much more restricted. In general, fossil 

 wood, submitted to distillation in the dry way, affords the same 

 quantities of gas as the fibre of unaltered wood ; but it yields 

 less water, and still less of that oil, of a peculiar and disagreeable 

 smell, by which all the brown coals are instantly recognised. 

 The empyreumatic acid is then only formed in very small quan- 

 tity ; but, on the other hand, the formation of alcohol is much 

 more considerable than in the case of unaltered vegetable fibre. 

 Those lignites or brown coals, which, from their external cha- 

 racters, visibly present a passage into black coal, afford in the 

 dry distillation water, with a very small quantity of fetid oil, and 

 often furnish so much as 70 per cent, of pure charcoal. 



Thus, therefore, says M. Karsten, those brown coals, the com- 

 mon BraunTcohle of Werner, from which the MoorhoJile of the same 

 mineralogist does not differ, in distillation surpass a great many 

 black coals, as to the quantity of charcoal obtained from them. 

 Add to this, that the specific gravity of these brown coals rises to 

 1.2881, and is consequently higher than that of several varieties 

 of black coal, which cannot be attributed to the quantity of 

 earthy matter and oxide of iron, since these brown coals fre- 

 quently do not contain one per cent, of them. 



The quantity of ashes afforded by fossil wood and brown coal 

 is very variable. In the species submitted to examination by 

 M. Karsten, it varies from three-fourths to more than fifty 

 per cent., which latter is the case with earthy brown coal. 

 This produces a serious inconvenience in the employment 

 of these combustibles ; for the ashes, by resting upon the 

 substance which is burning, oppose combustion to such a de- 

 gree, that a stronger current of air must be employed, than 

 the proper nature of the combustible, without this circumstance, 

 would require. Hence the great difficulty of employing this 

 substance advantageously for the purpose in view. The ashes 

 of fossil wood and brown coal contain no traces of fixed alkali. 

 Silica, alumina, oxide of iron, sulphate of lime, a little lime 



