198 
THE GEOLOGIST. 
varieties of combustibles, tbe degree of alteration of tlie organic 
tissue. 
The study of the peat has presented really no new fact. Besides 
the unaltered elementary organs which are met with in such great 
quantities in the fibrous peat, he has found according to the state 
of alteration of the combustible, variable proportions of those brown 
compounds — neutral or acid, azotized or non-azotized — which are 
designated under the general title of idmic comjjounds. 
The presence of these bodies, which have been already studied by 
M. Payen, nevertheless goes to establish a very clear distinction 
between the peats and the unaltered organic tissues. The chemical 
examination of the lig-nites ofiers more interest. 
In these researches distinction has been made between the lignites 
presenting still some woody structure, and those which oflPer 
the aspect and compactness of coal. The first constitute the xyloid 
lignite or fossil wood : the second form the compact or perfect lignite. 
In respect to chemical characters, all the varieties of lignite may be 
placed in one or other of these classes. 
Although the xyloid lignite may sometimes have the tenacity and 
the appearance of ordinary wood, he has recognized that in that 
combustible the woody tissue has experienced a great modification. 
It is reducible to a fine powder by trituration ; and submitted to 
the action of a weak solution of potash it yields to that alkali a con- 
siderable quantity of ulmic acid. 
The two following re-actions tend to establish a well-marked 
difference between the ordinary wood and xyloid lignite. 
When the azotic acid reacts at a high temperature on the wood it 
dissolves a part only of the fibres and medullary rays, and leaves the 
cellular matter quite pure, which dissolves without coloration in con- 
centrated sulphuric acid ; and possesses all the properties that M. 
Payen has studied with so much precision. 
Under the same circumstances the xyloid lig-nite is attacked with 
great energy and transformed into a yellow resin, soluble in alkalis 
and in an excess of azotic acid. 
When wood and xyloid lignite are comparatively submitted to the 
action of hypochlorites very marked differences between these two 
substances are likewise established. The hypochlorites exercise 
upon the wood a reaction, which, perhaps, may be compared to that 
of the azotic acid ; they dissove rapidly a part of the fibres and 
medullary rays, and leave the cellulose matter in a state of purity. 
The xyloid lignite is attacked by the alkaline hypochlorites ; is 
desolved nearly entirely by these reactives ; and leaves only imponder- 
able traces of fibre, and colourless medullary rays. 
It follows from the preceediug facts, that when the woody tissues 
have arrived at that state of modification which constitutes the 
xyloid lignite, still preserving the appearance of wood, they have 
experienced in their substance a great modification, and contain 
then direct new principles, characterized by their complete solu" 
bility in azotic acid and the hypochlorites 
