PEAT AND TURF 521 



PEARXi "WHITE or PEARXi POWDER is a sub-nitrate of bismuth. See 

 BISMUTH. 



PEAT AND TTTRI 1 . Accumulations of vegetable matter may be chiefly com- 

 posed either of succulent vegetation, grasses, or marsh plants, or of trees ; and tne 

 structure and condition of woody fibre is well known to be very different from that of 

 grasses and succulent plants. There are thus two very distinct kinds of material 

 preserved, the one undergoing change much less rapidly than the other, and perhaps 

 much less completely. It is easily proved that from the accumulation of forest trees 

 has been obtained the imperfect coal called lignite, while from marsh plants and 

 grasses, mixed occasionally with wood, we obtain peat, turf, and bog. All these sub- 

 stances consist to a great extent of carbon, the proportions amounting to from 50 to 

 60 per cent., and being generally greater in lignite than in turf. On the other hand, 

 the proportion of oxygen gas is generally very much greater in turf than in lignite. 

 The proportion of ash is too variable to be worth recording, but is generally sufficiently 

 large to injure the quality of the fuel. 



As a very large quantity of turf exists in Ireland, covering, indeed, as much as one 

 seventh part of the island, the usual and important practical condition of this substance 

 can be best illustrated by a reference to that countrj'. This will be understood by 

 the following account of its origin, abstracted from the ' Bog Eeport ' of Mr. Nimmo. 

 He says, referring to cases where clay spread over gravel has produced a kind of 

 puddle preventing the escape of waters-of floods or springs, and when muddy pools 

 have thus been formed, that aquatic plants have gradually crept in from the borders 

 of the pool towards their deep centre. Mud accumulated round their roots and stalks, 

 and a spongy semi-fluid was thus formed, well fitted for the growth of moss, which 

 now especially appeared ; Sphagnum began to luxuriate ; this absorbing a large quantity 

 of water, and continuing to shoot out new plants above, while the old were decaying, 

 rotting and compressing into a solid substance below, gradually replaced the water by 

 a mass of vegetable matter. In this manner the marsh might be filled up while the 

 central or moister portion, continuing to excite a more rapid growth of the moss, it 

 would be gradually raised above the edges, until the whole surface had attained an 

 elevation sufficient to discharge the surface-water by existing channels of drainage, 

 and calculated by its slope to facilitate their passage, when a limit would be, in some 

 degree, set to its further increase. Springs existing under the bog, or in its imme- 

 diate vicinity, might indeed still favour its growth, though in a decreasing ratio : and 

 here, if the water proceeding from them were so obstructed as to accumulate at its 

 base, and to Tceep it in a rotten fluid state, the surface of the bog might be ultimately 

 so raised, and its continuity below so totally destroyed, as to cause it to flow over the 

 retaining obstacle and flood the adjacent country. In mountain districts the progress 

 of the phenomenon is similar. Pools, indeed, cannot in so many instances be formed, 

 the steep slopes facilitating drainage, but the clouds and mists resting on the summits 

 and sides of mountains, amply supply their surface with moisture, which comes, too, 

 in the most favourable form for vegetation, not in a sudden torrent, but unceasingly 

 and gently, drop by drop. The extent of such bogs is also affected by the nature of 

 the rocks below them. On quarts; they are shallow and small ; on any rock yielding 

 by its decomposition a clayey coating they are considerable ; the thickness of the bog, 

 for example, in Knocklaid in the county of Antrim (which is 168 feet high), being 

 nearly 12 feet. The summit-bogs of high mountains are distinguishable from those 

 of lower levels by the total absence of large trees. 



As turf includes a mass of plants in different stages of decomposition, its aspect and 

 constitution vary very much. Near the surface it is light coloured, spongy, and 

 contains the vegetable-matter but little altered ; deeper, it is brown, denser, and more 

 decomposed ; and, finally, at the base of the greater bogs, some of which present a 

 depth of 40 feet, the mass of turf assumes the black colour, and nearly the density, of 

 coal, to which also it approximates very much in chemical composition. The amount 

 of ash contained in turf is also variable, and appears to increase in proportion as we 

 descend. Thus, in the section of a bog, 40 feet deep, at Tunahoe, those portions near 

 the surface contained 1| per cent, of ashes, the centre portions 3J per cent., whilst 

 the lowest four feet of turf contained 19 per cent, of ashes. In the superficial layers 

 it may also be remarked, that the composition is nearly the same as that of wood, 

 the succulent material being lost; and in the lower we find the change still more 

 complete. Notwithstanding these extreme variations, we may yet establish the ordi- 

 nary constitution of turf, and with certainty enough for practical use ; and, on the 

 average specimens of turf selected from various localities, the following results have 

 been obtained : 



The calorific power of dry turf is aboxit half that of coal ; it yields, when ignited 

 with oxide of lead, about 14 times its weight of lead. This power is, however, im- 

 mensely diminished in ordinary use by the water which is allowed to remain in its texture, 



