FOREIGN CORRESPONDENCE. 



199 



After having determined the chemical characters of xyloid lignite, 

 it was interesting to inquire if the compact lignite — which presented 

 no longer the texture of the woody tissues, which is black and shining- 

 like coal, and which often offers such analogies with this latter 

 substance as to put at fault the most experienced engineers — would 

 preserve the chemical character of the xyloid lignite, or would ally 

 itself with the coals. 



In a geological point of view this comparative study of the xyloid 

 lignite, compact lignite, and coal appears to possess a great impor- 

 tance. If there really existed a certain affinity between the state of 

 alteration of the combustible minerals, and the age of the rocks con- 

 taining them, one comprehends it would be of interest to geology to 

 possess a chemical character — independently of those pointed out by 

 M. Cordier — which would permit the exact appreciation of the degree 

 of modification of the organic body, and the determination of the age of 

 a rock by the state of alteration of the combustable mineral found in it. 



M. Fremy has applied himself, then, to find a series of chemical 

 reactions acting differently on the combustible minerals, and per- 

 mitting him to arrange the series of their varieties according to their 

 degrees of alteration, and the chemical characters they would thus 

 present. The reagents he employed were potash, the hypochlorites, 

 sulphuric acid, and nitric acid. 



Having pointed out the difference between woody tissue and xyloid 

 lignite, he goes on to show in what this latter differs from compact 

 lignite, which having lost all trace of its original organization is only 

 liable to be mistaken for certain varieties of coal. 



The manner of burning, the reaction of the volatile products of 

 combustion upon litmus, and the colour of the ashes form in them- 

 selves well-known distinctive characters, which chemical reagents 

 enable us to judge of with the greatest exactness. 



When, therefore, a compact lignite is submitted to the action of 

 strong potash the solution sometimes turns brown, and a small 

 quantity of ulmic acid is held in solution ; but generally this is not 

 the case, which fact immediately establishes a distinction between 

 compact and xyloid lignite. 



M. Fremy is of opinion that the lignites which resists the action of 

 potash are those nearest the coal-measures. 



The compact lignites, which in their brilliancy and blackness 

 resemble coal, aie entirely dissolved in the alkaline hypochlorites, 

 and are immediately acted upon by nitric acid, producing the yellow 

 resin before mentioned. 



These characters, then, render it easy to distinguish between lignite 

 and coal, as this latter mineral is not dissolved by the hypochlorites, 

 and is only slowly acted upon by nitric acid. On the former of these 

 tests M. Fremy lays great stress. 



Coal and anthracite, although resisting alkaline solutions and 

 hypochlorites, dissolve readily and completely in a mixture of con- 

 centrated sulphuric and nitric acids : the liquid becoming of a dark 



