424
DESSAU — DE STRUCTORS
on the St. Louis, Iron Mountain, and Southern Railway. Population (1890), 3960; (1900), 5611, of whom 332 were foreign-born and 364 negroes. Dessau, a town of Germany, capital of duchy of Anhalt, 2 miles south of the Elbe and 38 miles by rail southeast from Magdeburg. A new town hall was built in 18991900. Other new buildings are St Paul’s church (1890-92), a Roman Catholic church, the “ magistrates’ house ” (18721874), containing a library and drawings by Diirer, Holbein, Cranach, and State law courts; there are monuments to Moses Mendelssohn (1890), the Emperor William I. (1892), W. Muller (1891), who was a native of Dessau, and a war monument (1874). There are a small ducal library, a geological collection, the Leopold home for impoverished men (1750), and a picture gallery in the Amelia Institute. The various industries produce sugar, cloth, machinery, woollen yarn, carpets, blinds; ironfounding and gardening are also carried on ; an important corn market. Population (1885), 27,766; (1895), 42,375; (1900), 50,677. Desterro. See Florianopolis. Destructors.—The name destructors is applied by English municipal engineers to furnaces, or combinations of furnaces, constructed for the purpose of disposing by burning of town refuse, which is a heterogeneous mass of material, including, besides general household and ash-bin refuse, small quantities of garden refuse, trade refuse, market refuse, and often street sweepings. The mere disposal of this material is not, however, by any means the only consideration in dealing with it upon the destructor system. For many years past scientific experts, municipal engineers, and public authorities have been directing careful attention to the utilization of refuse as fuel for steam production, and such progress in this direction has been made of late that in many towns its calorific value is now being utilized daily in operating machinery. On the other hand, that proper degree of caution which is obtained only by actual experience must be exercised in the application of refuse fuel to steam-raising purposes. When its value as a low-class fuel was first recognized, the idea was disseminated that the refuse of a given population was of itself sufficient to develop the necessary steam-power for supplying that population with the electric light. The economical importance of a combined destructor and electric undertaking of this character naturally presented a somewhat fascinating stimulus to public authorities, and possibly has had much to do with the recent development both of the adoption of the principle of dealing with refuse by fire, and also of lighting towns by electricity. However true this phase of the question may be as the statement of a theoretical scientific fact, experience so far does not show it to be a basis upon which engineers may venture to calculate, although, as will be seen later, under certain circumstances of equalized load, which must be considered upon their merits in each case, a well-designed destructor plant can be made to perform valuable commercial service to an electric or other power-using undertaking. Further, when a system, thermal or otherwise, for the storage of energy can be introduced and applied in a trustworthy and economical manner, the degree of advantage to be derived from the utilization of the waste heat from destructors will be materially enhanced. The composition of house refuse, which must obviously affect its calorific value, varies considerably in different localities, accordto thelycondition, habits, and pursuits of the people. Compos • ing j'rom ana Ses it is found that average London ash-bin ,0 a ° refuse contains in theInaverage proporre fuse. tions given in the the constituents following table. the northern towns, where the privy and ash-pit system is in use, excrementitious matter also occurs in the refuse.
Average London Ash-bin Refuse. Constituents. Breeze (cinder and ashes) Fine dust Vegetable, animal, and various mineral matters Waste paper. Straw, fibrous material, and rags . Bottles, crockery, and broken glass Coal and coke Tins and iron Bones . Total .
Percentages by Weight. 63-69 19-51 4-61 4-28 3-61 1-98 •84 1-00 •48 100-00
Manchester Refuse. Constituents. Ashes and excreta in pails Dust and cinders . Fish and bones Animal refuse, as dogs, cats, hens, rabbits, &c. Boots, hats, rags, paper, &c. . Vegetable refuse . Glass, pottery, bricks, &c. Old iron and tin Total .
Percentages by Weight. 64-50 34-55 •15 •05 •05 •05 •60 •05 100-00
In London the quantity of house refuse amounts approximately to II million tons per annum, which is equivalent to from 4 cwt. to 5 cwt. per head per annum, or to from 200 to 250 tons per 1000 of the population per annum. Statistics, however, vary widely in different districts. In the vicinity of the metropolis the amount varies from 2 -5 cwt. per head per annum at Leyton to 3 -5 cwt. at Hornsey, and to as much as 7 cwt. at Ealing. In the north of England the total house refuse collected, exclusive of street sweepings, amounts on the average to 8 cwt. per head per annum. Speaking generally, throughout the country an amount of from 5 cwt. to 10 cwt. per head per annum should be allowed for. A cubic yard of ordinary house refuse weighs from 12j to 15 cwt. Shop refuse is lighter, frequently containing a large proportion of paper, straw, and other light wastes. It sometimes weighs as little as 7| cwt. per cubic yard. A load, by which refuse is often estimated, varies in weight from 15 cwt. to 11 tons. The question how a town’s refuse shall be disposed of must be considered both from a commercial and a sanitary point of view. Various methods have been practised. Sometimes the n. household ashes, &c., are mixed with pail excreta, or ,sP°sa • with sludge from a sewage farm, or with lime, and disposed of for agricultural purposes, and sometimes they are conveyed in carts or by canal to outlying and country districts, where they are shot on waste ground or used to fill up hollows and raise the level of marsh land. Such plans are economical when suitable outlets are available. To take the refuse out to sea in hopper barges and sink it in deep water, as is done, for example, at Liverpool and New York, is usually expensive and frequently unsatisfactory. At Bermondsey, for instance, the cost of barging is about 2s. 9d. a ton, while the material may be destroyed by fire at a cost of from lOd. to Is. a ton, exclusive of interest and sinking fund on the cost of the works. In other cases, as at Chelsea and various dust contractors’ yards, the refuse is sorted and its ingredients are sold ; the fine dust may be utilized in connexion with manure manufactories, the pots and pans employed in forming the foundations of roads, and the cinders and vegetable refuse burnt to generate steam. In the Arnold system, carried out in Philadelphia and other American towns, the refuse is sterilized by steam under pressure, the grease and fertilizing substances being extracted at the same time ; while in other systems, such as those of Weil and Porno, and of Defosse, distillation in closed vessels is practised. But the destructor system, in which the refuse is burned to an innocuous clinker in specially constructed furnaces, is that which must finally be resorted to, especially in districts which have become well built up and thickly populated. Various types of furnaces and apparatus have from time to time been designed, and the subject has been one of much experiment and many failures. The principal towns in England which took the lead in the adoption of the refuse destructor system _es truewere Manchester, Birmingham, Leeds, Heckmondwike, , 0 Warrington, Blackburn, Bradford, Bury, Bolton, Hull, Nottingham, Salford, Ealing, and London. Ordinary furnaces, built mostly by dust contractors, were in use in London and in the north of England some forty years ago, but they were not scientifically adapted to the purpose, and necessitated the admixture of coal or other fuel with the refuse to ensure its cremation. The Manchester Corporation erected a furnace of this description about the year 1873, and Messrs Mead and Co. made an unsatisfactory attempt in 1870 to burn house refuse in closed furnaces at Paddington. In 1876 Mr Fryer erected his destructor at Manchester, and several other towns adopted this furnace shortly afterwards. Other furnaces were from time to time brought before the public, among which may be mentioned those of Pearce and LuptcJn, Pickard,
