Destructors, Refuse, the apparatus or plant used in the cremation of house and factory refuse. Formerly refuse from large towns and populous areas was either disposed of for manurial purposes or spread over waste land, where its presence speedily became a nuisance. The consequent danger to the public health, coupled with the increasing difficulty and cost of its disposal, led to attempts being made to deal with it by more sanitary methods. The first attempts to cremate it in a closed furnace on a large scale, made in London in 1870, were not successful, primarily owing to the unscientific design of the furnace. In 1877, however, there was built in Manchester the forerunner of the
modern destructor, to the designs of the late Mr. Alfred Fryer. This consisted of two simple cells, the primary feature of the design being 'the charging of the refuse into the back of the furnace, and drawing out the resulting clinker from the front'. With certain modifications, this design is in general use at the present time. The basic principles underlying their scientific design may be summed up in the following points: (a) Charging at regular intervals, the refuse being dumped into a hopper, and fed into the back of the furnace as a charge, means being taken to prevent undue escape of gases. The moisture having evaporated, the material may then be raked forward onto the fire-bars, where combustion takes place. (b) To avoid nuisance, the resulting gases must be inodorous, which requires a temperature of about 2000°F. This is obtained by passing the products of combustion over the hottest portion of the fire, prior to their passage into the main flue. (c) Removal of the fine dust and particles in suspension in the flue gases by means of spiral chambers at the base of chimney. (d) Provision of forced draught. A well-designed plant should show little, if any, suspended matter in the gases on emission from the chimney. Formerly no use was made of the heat generated, but modern installations now invariably have steam-raising plant incorporated in the design. This power is commonly used to generate electricity. Some portion may be utilized in crushing and screening the clinker, which is frequently used in making slab-paving, or ground fine and used as a substitute for sand in mortar. The following data may be found of service: (a) 60 per cent of the average refuse is combustible. (b) The calorific value may be taken as being one-seventh that of good steam-coal. (c) 100 electrical units may be obtained from each ton of refuse consumed. (d) With forced draught, as much as 100 lb. of refuse has been burnt per square foot of grate area per hour. (e) 250 tons of refuse per annum per 1000 of population may be estimated for.—Bibliography: W. H. Maxwell, Removal and Disposal of Town Refuse; Kempe, Engineer's Year Book.
Destutt de Tracy, Antoine Louis Claude, French philosophical writer, born in 1754 of a family of Scottish extraction, died in 1836. As a philosopher he belonged to the Sensationalist school, and considered all our knowledge to be derived originally from sensation. He has been called the logician and metaphysician of the school of Condillac. Among his chief works are: Idéologie (1801), Logique (1805), and Traité de la Volonté (1815).
Deter´minant, a mathematical expression which appears in the solution of a system of equations of the first degree.
The solution of the equations
a1x + b1y = c1,
a2x + b2y = c2,
is given by
x(a1b2 - a2b1) = c1b2 - c2b1,
y(a1b2 - a2b1) = a1c2 - a2c1.