the different kinds of Coal. 61 



other hand, from the extreme difficulty of making such analyses 

 as these in the dry way, M. Karsten considered it as almost im- 

 possible to analyse a great number of coals in this manner. He 

 therefore made choice of a certain number of mineral combus- 

 tibles, which present the most striking differences during distil- 

 lation in the dry way. 



The specimens selected, to the number of eleven, are minera- 

 logically described, and were carefully submitted, on the one 

 hand, to distillation in the dry way, and on the other to chemical 

 analysis. They consisted of fossil wood and brown coal of the 

 countries bordering upon the Rhine, of various black coals of 

 Upper Silesia, the country of Saarbruck, of other parts of 

 Prussia, and of the mines of England. To the results of his 

 eleven chemical analyses, M. Karsten, in order to complete the 

 comparison which he proposed to himself to establish between 

 the different combustibles, has added the result which MM. 

 Gay Lussac and Thenard obtained by their analysis of beech 

 wood. 



The author in this manner forms a synoptical table of twelve 

 combustibles, which he takes for general terms of comparison. 

 This table, founded as well upon M. Karsten's analyses, as up- 

 on the data admitted by M. Berzelius in the atomic theory, 

 supposes in fact, that, in each of the combustibles essayed, a 

 thousand atoms of carbon are combined with a certain number 

 of atoms of oxygen and of atoms of hydrogen. The author 

 then determines by calculation, how many atoms of hydrogen 

 occur in each of these substances, for a thousand atoms of oxy- 

 gen. 



Before proceeding to the important conclusions which the au- 

 thor draws from his results, it will be proper to point out briefly 

 the manner in which he proceeds. 



In the first place, M. Karsten informs us, that in coal he has 

 in vain searched for muriatic acid, iodine, phosphoric acid, and 

 oxide of chrome. The quantity of earths and oxide of iron, 

 which remains after the incineration of coal, that is to say, their 

 contents in ashes, is very variable. One sort of coal leaves on- 

 ly 1 per cent, of ashes, and consequently less than any species of 

 wood. In another kind of coal, the contents in ashes rise to 

 above 20 per cent. The earths which occur in various propor- 



