108 



THE GEOLOGIST. 



varieties of combustibles, the degree of alteration of the 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 ulmic compounds. 



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 lignites offers more interest. 



In these researches distinction has been made between the lignites 

 presenting still some woody structure, and those which offer 

 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 aeid ; and possesses all the properties that M. 

 Payen has studied with so much precision. 



Under the same circumstances the xyloid lignite 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 proceeding 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 

 bhen direct new principles, characterized by their complete solu- 

 bility in azotic acid and the hypochlorites 



