Page:The American Cyclopædia (1879) Volume IV.djvu/753

Rh the vegetable remains must then have attained in favorable localities a thickness at least double that of the present peat deposits. The supposition that the plants at the carboniferous epoch contained more bitumen than those of our time has no foundation whatever, as bitumen is obtained from peat in as large proportion as from coal. Mineral oil, which also results, in its essential part at least, from the decomposition of vegetable matter, is in this particular only comparable to coal; but it is produced from marine plants which have no fibrous tissue, but merely cellular matter.—After reading the foregoing descriptions of the growth of peat, the admirable simplicity of the process used by nature to reach its end in providing deposits of combustible minerals in the several geological periods is evident enough. This identity, however, can be still more positively proved by comparing the chemical operations attending these formations, and the absolute similarity of the elements which compose the different matters known under the names of peat, lignite, coal, and anthracite. The composition of these combustible materials, as they are generally called, compared with that of wood and of woody plants which by their characters and texture are related to the most common species of the coal measures, and which enter into the composition of peat in our time, is presented in the following table compiled from Dana's “Manual:”

This table shows in lycopodium species and equisetum about the same composition as in wood. These correspond in structure, and have at the same time a generic relation to the species forming the essential compounds of coal as recognized by microscopical examination, viz.: lepidodendron, sigillaria, and calamites. The sphagnum, which enters more than any other plant into the composition of peat, has more carbon than lycopods, even slightly more than wood. In the decomposition of the woody matter two different processes are recognized by chemistry. Decayed wood taken from the interior of trunks of dead trees exposed to atmospheric action gives by analysis, on the average, carbon 47.62, hydrogen 6.18, oxygen 44.87; which compared with wood, C. 49.66, H. 6.21, O. 43.03, indicates that through this decomposition a proportion of carbon has been taken from the wood, while the hydrogen is slightly increased. The elements of water therefore, and an amount of oxygen, have become united with the wood, while carbonic

acid has been separated from it. This comparison of analyses exemplifies the well known fact that the decomposition of plants under atmospheric influences returns to the atmosphere the carbonic acid absorbed by the vegetation, which by nutrition of the living plants is transformed into wood. But when the woody matter is protected against the action of the oxygen of the air, as it is in vegetable remains under water or covered by mosses impregnated with water, the chemical changes as proved by analyses assume another form. This is the case in the formation of peat, which when ripe has C. 59.5, H. 55, O. 33, or compared with wood an increased amount of carbon in proportion with a diminution of oxygen, separated into carbonic acid with a little of the hydrogen of the wood. The amount of carbon in peat, as in all the mineral combustibles, is extremely variable; in young sphagnum peat it is no more than 51 to 52 per cent., while in old peat it is as high as 61 to 62 per cent. The proportion of bitumen increases in peat in the same degree. Taken from old beds, this matter has yielded by distillation 30 per cent. of bitumen. To obtain it, the distillation of peat has been practised for many years on the bogs of the Jura in Switzerland; and peat from the bogs of Ireland is also distilled in large establishments for manufacturing candles. This sufficiently answers the objection made against the theory of the formation of coal from heaped vegetables by annual growth like beds of peat, and the mistaken assertion that peat has no bitumen and therefore cannot form coal. The composition of peat as given above does not differ much from that of the more recent lignite of Germany, showing therefore the same process of chemical action. These lignite beds, mentioned before, are heaps of trunks overlaid by thick strata of sand and clay. The wood is black and quite soft, but its texture is still as well preserved and as distinct as in living trees. The matter in its purity has C. 57.28, H. 6.03, O. 36.10, or a less amount of carbon than old peat, with more oxygen; thus proving that the process of decomposition is exactly the same, but that it is in a less advanced stage. In lignite of an older formation the analysis indicates C. 68.7, H. 5.5, O. 25; therefore an increase of carbon, still resulting from the same combination, the diminution of the oxygen and of a little of the hydrogen of wood. As in peat, the amount of carbon in lignite is very variable, which results especially from the nature of the original compounds. The lignite of the old tertiary of the Rocky mountains, which in many beds has the same appearance, lamination, and nearly the density of the true coal, has only 51 per cent. of carbon in an average taken from the comparison of 21 analyses of the matter from many localities. This reduced amount of carbon is apparently due to the great proportion of palm wood and palm remains which entered originally into its composition. The average composition of the best