FOREIGN CORRESPONDENCE. 
190 
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 difierence 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 
