CHEMICAL SCIENCE. 205 



dissolves without coloration in concentrated sulphuric acid, and pos- 

 sesses all the properties ascribed to it by M. Pay en. 



Under the same circumstances, fossil-wood lignite is attacked with 

 great energy and completely transformed into a yellow rosin, soluble 

 in alkalies and in excess of nitric acid. 



By submitting wood and fossil-wood lignite comparatively to the 

 action of hypochlorites, there is a marked difference in their effects 

 on the two substances. 



Hypochlorites react on wood in a manner which may be compared 

 to that of nitric acid. They dissolve rapidly a portion of the fibres 

 and medullary rays, leaving the cellulose untouched. 



Alkaline hypochlorites attack fossil-wood lignite, almost entirely 

 dissolving it, leaving only imponderable colorless traces of the fibres 

 and medullary rays. 



It results, then, from the preceding facts, that when ligneous tissues 

 arrive at that state of modification constituting fossil-wood lignite, and 

 while preserving the .appearance of wood, their substance has under- 

 gone a very material modification, and then contains new proximate 

 principles, characterized by their perfect solubility in nitric acid and 

 in hypochlorites. 



After determining the chemical characteristics of fossil-wood lig- 

 nite, it becomes interesting to ascertain whether the compact lignite, 

 in which the texture of the ligneous tissues is no longer observable, 

 and which is black and brilliant like coal, to winch it bears so much 

 analogy as to mystify the most experienced, preserves the chemical 

 characteristics of fossil-wood lignite, or whether it resembles coal. 



In a geological point of view, the comparative study of fossil-wood 

 lignite, of compact lignite, and of coal, appears to me to be also of 

 great importance. If, in fact, there is a positive connection between 

 the state of alteration of combustible minerals and the age of the strata 

 containing them, it becomes apparent how much geology would benefit 

 by possessing a chemical character, by means of which it would be 

 possible to determine accurately the extent of the modification of an 

 organic body, and of determining the age of the stratum by the state 

 of alteration of the combustible mineral found therein. Therefore I 

 have applied myself to find a series of chemical re-agents acting differ- 

 ently on combustible minerals, and to arrange their varieties con- 

 formably to the degree of their modifying action and the chemical 

 characters they would thus present. The re-agents I have employed 

 are potash, hypochlorites, sulphuric and nitric acids. I also take into 

 account the excellent characteristic given by M. Cordier. 



I have previously shown that it is impossible to confound ligneous 

 tissue with fossil-wood lignite, the latter being soluble in hypochlo- 

 rites and nitric acid. Compact lignite, presenting no longer the ap- 

 pearance of organization, could be confounded only with certain 

 varieties of coal. The mode of combustion, the reaction of the vol- 

 atile products on litmus, and the color of the dust, constitute already 

 distinctive and very important characteristics. To this subject chem- 

 ical re-agents will give a yet greater degree of certainty. When 

 compact lignite is submitted to the action of concentrated potash, the 

 liquid sometimes becomes colored brown, dissolving a small quantity 

 of ulmic acid ; but alkaline liquid does not generally react on the 

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