114 



AGRICULTURAL CHEMISTRY. 



All varieties of wood coal, from whatever 

 Btrata they may be taken, contain more hy- 

 drogen than wood does, and less oxygen 

 than is necessary to form water with this 

 hydrogen; consequently they must all be 

 produced by the same process of decompo- 

 sition. The excess of hydrogen is either 

 hydrogen of the wood which has remained 

 ill it unchanged, or it is derived from some 

 exterior source. The analysis of wood coal 

 from Ringkuhl, near Cassel, where it is 

 seldom found in pieces with the structure of 

 wood, gave, when dried at 212, 



Carbon 



Hydrogen 



Oxygen 



Ashes 



62-60 



5-02 



26-52 



5-86 



6383 

 4-80 



25-51 

 5-86 



100-00 



100-00 



The proportions derived from these num- 

 bers correspond very closely to the formula 

 C 32 H 15 O 9 , or they represent the constitu- 

 ents of wood, from which the elements of 

 carbonic acid, water, and 2 equivalents hy- 

 drogen, have been separated. 



C36H22 O2>2+Wood. 



Subtract C 4 H 7 O13-(- 4 atoms carbonic acid-^- 



5 atoms of water 



2 atoms of hydrogen. 



C32 H15 O 9= Wood Coal from Ring- 

 kuhl. 



The formation of both these specimens of 

 wood coal appears from these formulae to 

 have taken place under circumstances which 

 did not entirely exclude the action of the air, 

 and consequent oxidation and removal of a 

 certain quantity of hydrogen. Now the 

 Laubacher coal is covered with a layer of 

 basalt, and the coal of Ringkuhl was taken 

 from the lowest seam of layers, which pos- 

 sess a thickness of from 90 to 120 feet; so 

 that both may be considered as well protected 

 from the air. 



During the formation of brown coal, the 

 elements of carbonic acid have been sepa- 

 rated from the wood either alone, or at the 

 same time with a certain quantity of water. 

 It is quite possible that the difference in the 

 process of decomposition may depend upon 

 the high temperature and pressure under 

 which the decomposition took place. At 

 least, a piece of wood assumed the character 

 and appearace of Laubacher coal, after be- 

 ing kept for several weeks in the boiler of a 

 steam engine, and had then precisely the 

 same composition. The change in this case 

 was effected in water, at a temperature of 

 from 3340 to 3520 p. (150 160 C.,) and 

 under a corresponding pressure. The ashes 

 of the wood amounted to 0-51 per cent. ; a 

 little less, therefore, than those of the Lau- 

 hacher coal ; but this must be ascribed to 

 the peculiar circumstances under which it 

 was formed. The ashes of plants examined 

 by Bemier amounted always to much more 

 than this. 



The peculiar process by which the de- 

 composition of these extiait vegetables has 



been effected, namely, a disengagement of 

 carbonic acid from their substance, appears 

 still to go on at great depths in all the layers 

 of wood coal. At all events it is remarkable 

 that springs impregnated with carbonic acid 

 occur in many places, in the country be- 

 tween Meissner, in the electorate of Hesse, 

 and the Eifel, which are known to possess 

 large layers of wood coal. These springs 

 of mineral water are produced on the spot 

 at which they are found ; the springs of 

 common water meeting with carbonic acid 

 during their ascent, and becoming impreg- 

 nated with it. 



In the vicinity of the layers of wood coal 

 at Salshausen (Hesse Darmstadt) an excel- 

 lent acidulous spring of this kind existed a 

 few years ago, and supplied all the inhabi- 

 tants of that district; but it was considered 

 advantageous to surround the sides f the 

 spring with sandstone, and the consequence 

 was, that all the outlets to the carbonic acid 

 were closed, for this gas generally gains ac- 

 cess to the water from the sides of the 

 spring. From that time to the present this 

 valuable mineral water has disappeared, and 

 in its place is found a spring of common 

 water. 



Springs of water impregnated with car- 

 bonic acid occur at Schwalheim, at a very 

 short distance from the layers of wood coal 

 at Dorheim. M. Wilhelmi observed some 

 time since, that they are formed of commoa 

 spring water which ascends from below, 

 and of carbonic acid which issues from the 

 sides of the spring. This same fact has 

 been shown to be the case in the famed 

 Fachinger spring, by M. Schapper. 



The carbonic acid gas from the springs in 

 the Eifel is, according to BischofF, seldom 

 | mixed with nitrogen or oxygen, and is pro- 

 bably produced in a manner similar to that 

 just described. At any rate the air does 

 not appear to take any part in the formation 

 of these acidulous springs. The carbonic 

 acid has evidently not been formed either by 

 a combustion at high or low temperatures ; 

 for if it were so, the gas resulting from the 

 combustion would necessarily be mixed with 

 of nitrogen, but it does not contain a trace 

 of this element. The bubbles of gas which 

 escape from these springs are absorbed by 

 caustic potash, with the exception of a resi- 

 duum too small to be appreciated. 



The wood coal of Dorheim and Salzhau- 

 sen must have been formed in the same way 

 as that of the neighbouring village of Lau- 

 bach ; and since the latter contains the exact 

 elements of woody fibre, minus a certain 

 quantity of carbonic acid, its composition 

 indicates very plainly the manner in which 

 j it has been produced. 



The coal of the upper bed is subjected to 

 an incessant decay by the action of the air, 

 by means of which its hydrogen is removed 

 in the same manner as in the decay of wood. 

 This is recognised by the way in which it 

 burns, and by the formation of carbonic arid 

 in the mines. 



