1879J TAtf Formation of Coal. 679 
the cells, and unites them. It is dissolved by caustic 
alkalies. 
After these internal tissues M. Fremy studied the bodies 
which cover and protect them, such as the cuticle. He 
called by the name of cutose the substance which forms the 
cuticle, and which is even found in cork. It is remarkable 
for its fixity, and is scarcely affeCted by sulphuric acid. 
Lastly, to complete this general study, the learned Director 
of the Museum examined those bodies which are most fre- 
quently met with in the tissues. Gum, for instance, is not 
a neutral substance, as has been commonly supposed, but a 
veritable salt, resulting from the combination of a genuine 
acid with lime. The chlorophyllus itself is not a neutral 
substance. It is formed of a bluish-green alkaline salt, 
phyllocyanate of potassa. 
These preliminary researches being concluded, M. Fremy 
placed the top stone to the edifice by attempting the solu- 
tion of the difficult and interesting problem of the formation 
of fossil fuel. If vegetable palaeontology has made such 
great progress in these latter times, it may be said that the 
chemical part of the question has remained in absolute 
darkness. We know not under what influences the vegetable 
organisation has been destroyed to form this black bitu- 
minous mass, partly fusible, non-organic, and insoluble in 
dissolvents, which constitutes coal. This substance neither 
resembles the pyrogenous bodies produced in our labora- 
tories nor the ligneous tissues which have formed it. By 
distillation it gives forth volatile produces which do not 
resemble those given by wood. It leaves also, as a fixed 
body, a special substance called coke, which is very different 
from charcoal. 
Having already introduced this question in a previous 
paper, M. Fremy mentioned several chemical reactions 
which characterised wood, peat, lignite, coal, and anthra- 
cite. Wood is not perceptibly affeCted by a diluted solution 
of potassa, whereas peat often renders to this alkali con- 
siderable quantities of ulmic acid. Xyloide lignite, or fossil 
wood, also contains notable proportions of ulmic acid ; but 
it is not to be confounded either with wood or with peat, 
because it is transformed into yellow resin by nitric acid, 
and is completely soluble in hypochlorites. Compact or 
perfect lignite does not contain any sensible quantity of 
ulmic acid, but is soluble in nitric acid and hypochlorites. 
With respeCt to coal and anthracite, they are characterised 
by their insolubility in all the neutral solvents, acids, alkalies, 
and hypochlorites. 
