302 +2.520 5 feet 60 inches and 2.5 × 2 906.25 = 181.25 inches, or 15 feet 1 inch radius. 79. Coals in quality vary considerably for the economic production of steam; thus, 1 lb. of the best Welsh is capable of evaporating 9.49lbs. of water; 1 lb. of the best Newcastle, 9.01 lbs. ; and Derbyshire, only 6.77 lbs.: the average capacity in steam-vessels for stowage of fuel, is from 45 to 48 cubic feet per ton. Now, supposing by measurement there be found remaining in the boxes 168 tons, and the average consumption 221 cwt. per hour-how many hours' steaming may there be expected from that quantity, at an equal ratio of expenditure? and how many tons of Newcastle coals must be supplied, by which to produce equal amounts of effect? Scotch and Welsh coals, in a state for fuel, re quire per ton about 44 cubic feet capacity for stowage; and Newcastle coal, in a similar state, 46 cubic feet. 80. What is meant generally by the term combustion? Combustion, under ordinary circumstances, means, chemical union of combustible matter with oxygen at a sufficiently elevated temperature for the generation of heat. Ignition, spontaneously or mechanically, is the source through which increased temperature is incited, and oxygen is the matter by which combustion is supported. Any combustible substance employed commonly for the purpose of creating and maintaining heat, is termed fuel; but coal, of which there are many varieties, is the principal substance as fuel used in this country, the following of which are the mean of compositions per cent. from different localities. Specific Amount per cent. of gravity. Carbon. Hydrog. Nitrog. Sulph. Oxygen. Ash. 1.279 80.40 5.29 6.04 1.34 7.67 4.05 8 pounds of fresh water, evaporated from 212° Fah. by 1 pound of coal, is the average quantity. 81. What are the effects of heat upon liquid substances generally? 1. Liquefaction,-as the conversion of ice to water. 2. Expansion,-as the increased bulk of water from 39° to 212° Fah. 3. Vaporization, as the change of water to steam by excess of caloric after 212°; or any other boiling-point to which it may be exposed by constrained pressure. 82. What are the effects of cold upon liquid substances generally? 1. Liquefaction, as the condensation of steam through abstraction of heat by cold water. 2. Contraction, as the reduction of steam as a vapour to water as a liquid. 3. Solidification, as the change which water undergoes by reduction of temperature-namely, from a liquid to ice in a solid state. But water from a liquid to that of a solid state is an exception to effects produced upon bodies generally; for at 39° Fah. water is at its greatest degree of density, or 1.00000; whereas, at 32°, or point of freezing, its bulk is increased to 1.00012. 83. Are vapours, liquids, and solids expanded regularly by regular increments of heat? Atmospheric air, gases, and vapours generally, expand regularly with every increase of temperature, or are similarly augmented in elastic force, if enlargement of bulk be prevented. Hence, whatever amount of expansion will arise by an increased temperature of 12°, half as much will arise from an increase of 6°, twice as much from 24°, &c.; but neither liquids nor solids follow this law. Thus, when water is at 40° Fah. its density equals 1.00000 Glass rod in linear dimensions expands from unity or 1.000000: 32 to 212° Fah. 1.000861 212.. 392 66 1.000918 And the length of the following metals at 62° Fah. being 1.000000: Iron, cast at 2120 Fah. 1.000893-at 662° 1.003943, fusing-point 1.016389. 84. For practical or engineering purposes, how are metals ranged in regard to their power of conducting heat? In the following order and ratio: 85. For practical purposes, as that of retaining heat in pipes, &c., what are the worst conductors? Stones, bricks, earthenware, glass, lint, sheep's wool, raw silk, and fur, are successively lower than each other in conducting powers. |