1911 Encyclopædia Britannica/Peat

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PEAT (possibly connected with Med. Lat. petia, pecia, piece, ultimately of Celtic origin; cf. O. Celt. pet, O. Ir. pit, Welsh peth, portion), a product of decayed vegetation found in the form of bogs in many parts of the world. The continent of Europe is estimated to contain 212,700 sq. m. of bog; Ireland has 2,858,150 acres, Canada 30,000,000 acres, and the United States 20,000,000 acres. The plants which give origin to these deposits are mainly aquatic, including reeds, rushes, sedges and mosses. Sphagnum is present in most peats, but in Irish peat Thacomitrum lanuginosum predominates. It seems that the disintegration of the vegetable tissues is effected partly by moist atmospheric oxidation and partly by anaerobic bacteria, yeasts, moulds and fungi, in depressions containing fairly still but not stagnant water, which is retained by an impervious bed or underlying strata. As decomposition proceeds the products become waterlogged and sink to the bottom of the pool; in the course of time the deposits attain a considerable thickness, and the lower layers, under the superincumbent pressure of the water and later deposits, are gradually compressed and carbonized. The most favourable conditions appear to be a moist atmosphere, and a mean annual temperature of about 45° F.; no bogs are found between latitudes 45° N. and 45° S.

Peat varies from a pale yellow or brown fibrous substance, resembling turf or compressed hay, containing conspicuous plant remains, to a compact dark brown material, resembling black clay when wet, and some varieties of lignite when dry. Two typical forms may be noticed: “Hill peat” (the mountain or brown bogs of Ireland), found in mountainous districts, and consisting mainly of Sphagnum and Andromeda; and “Bottom peat” (the lowland or red bogs of Ireland), found in lakes, rivers, and brooks, and containing Hypnum. It always contains much water, up to 90%, which it is necessary to remove before the product can be efficiently employed as a fuel, and for most other purposes. A specimen dried at 100° C. had the composition: carbon=60.48%, hydrogen=6.10%, oxygen=32.55%, nitrogen=0.88%, ash=3.30%; the ash is very variable—from 1 to 65%—and consists principally of clay and sand, with lesser amounts of ferric oxide, lime, magnesia, &c. The specific gravity has been variously given, owing to the variable water content and air spaces; when dried and compressed, however, it is denser than water.

Peat-winning presents certain special features. The general practice is to cut a trench about a foot deep with a peculiarly shaped spade, termed in Ireland a “slane,” and remove sods from 3 to 4 ft. long. When one layer has been removed, the next is attacked, and so on. If the deposit be more solid step working may be adopted, and should water be reached recourse may be had to long-handled slanes. The sods are allowed to drain, and then stacked for drying in the air, being occasionally turned so as to dry equally; this process may require about six weeks. The dried sods are known as “dug peat.” Excavators and dredges are now extensively used, and the drying is effected in heated chambers, both fixed and revolving.

The low value of ordinary dug peat as a fuel has led to processes for obtaining a more useful product. In M. Ekenberg’s process the wet peat is pulped and milled so as to make it of uniform composition, and the pulp passed into an oven maintained at 180°–200° F., where it is carbonized by superheated water. The pressed product, which resembles lignite, still contains 8 to 14% of water; it is is driven off by heat, and the residue briquettes. The final product is nearly equal to coal in calorific value and has the additional advantage of a lower sulphur content—0.2 to 0.4% against about 2% in ordinary coal. M. Zeigler’s method leads to the production of a useful coke. Both these processes permit the recovery of valuable by-products, especially ammonium sulphate. Experiments for obtaining a gas suitable for consumption in gas-engines have been followed by commercial processes devised by the Mond Gas Corporation, London, and Crossley Bros. of Manchester, and by Caro and Frank in Germany. The processes essentially consist in destructively distilling peat in special retorts and under specified conditions, and, in addition to the gas, there is recovered a useful coke and also the nitrogen as ammonium sulphate.

The conversion of the nitrogen into ammonia has been the subject of much work, and is commercially pursued at a works at Carnlough, Co. Antrim, under patents held by H. C. Woltereck. The peat is treated with a mixture of air and water vapour in special furnaces, and the gaseous products, including paraffin tar, acetic acid and ammonia, are led through a special scrubber to remove the tar, then through a tower containing milk of lime to absorb the acid (the calcium acetate formed being employed for the manufacture of acetone, &c.), and finally through a sulphuric acid tower, where the ammonia is converted into ammonium sulphate which is recovered by crystallization.

Peat has also been exploited as a source of commercial alcohol, to be employed in motors. In the process founded on the experiments of R. W. Wallace and Sir W. Ramsay, which gives 25 to 26 gallons of spirit from a ton of peat, the peat is boiled with water containing a little sulphuric acid, the product neutralized with lime and then distilled, the ammonia is a so recovered. In another process a yield of 40 gallons of spirit and 66 ℔ of ammonium sulphate per ton of peat is claimed.

Of other applications we may notice C. E. Nelson’s process for making a paper, said to be better than ordinary wrapping; the first factory to exploit this idea was opened at Capac, Michigan, in 1906. Peat has been employed as a manure for many years, and recently attempts have been made to convert artificially its nitrogen into assimilable nitrates; such a process was patented by A. Muntz and A. G. Girard of Paris, in 1907.

See P. R. Björling and F. T. Gissing, Peat and its Manufacture (1907); F. T. Gissing, Commercial Peat (1909); E. Nystrom, Peat and Lignite (1908), published by Department of Mines of Canada.