§ 26. LIEBIG ON THE FORMATION OF COAL. 701 



saccharine fermentation is induced, and the grass acquires 

 a peculiar fragrance and sweetness ; but in wet seasons, 

 when the hay is prematurely heaped together, the volatile 

 principles cannot escape from the inner mass of vegetable 

 matter, heat is rapidly evolved, a dense vapour exhales, 

 and at length flames break forth, and the stack is consumed. 

 When the process is interrupted, and combustion prevented, 

 the hay is found to have acquired a dark-brown colour, a 

 glazed or oily surface, and a bituminous odour. Were 

 vegetable substances, under the circumstances here de- 

 scribed, placed beneath great pressure, so as to confine the 

 gaseous principles, bitumen, lignite, or coal, might be pro- 

 duced, according to the various modifications of the process. 

 Mr. Parkinson thus traces vegetable matter through every 

 stage of the saccharine, vinous, acetous, and bituminous 

 fermentations; producing alcohol, ether, naphtha, petroleum, 

 bitumen, amber, and even the diamond ; and explains that 

 by the process of bituminization, stems and branches have 

 been converted into brown coal, lignite, jet, coal, and 

 anthracite. 



26. Liebig on the formation of Coal. — The nature 

 of these changes is thus explained by the eminent chemist, 

 Baron Liebig. Vegetable substances after death undergo 

 two processes of decomposition ; namely — 



1st. Fermentation or decay, which is as low process of combustion, 

 in which the combustible parts of a plant unite with the oxygen 

 of the atmosphere ; for the decay of woody fibre in contact with 

 air or oxygen, converts the latter into an equal volume of car- 

 bonic acid; the presence of water and a certain temperature 

 being necessary. Woody fibre in a state of decay forms humus. 



2dly. Mouldering or putrefaction of wood subjected to the action of 

 water, and more or less excluded from the air. When pure 

 ligneous fibre, as linen, for example, is placed in contact with 

 water, considerable heat is evolved, and the vegetable matter 

 loses its coherence, and becomes a soft friable mass ; in short, 

 it undergoes a true putrefaction. 



When all access to air is excluded and consequent oxidation and a 

 removal of a certain quantity of hydrogen, then other changes ensue, 



