ENGINE AT THE CITY SAW MILLS.
FURNACE AT THE CITY SAW MILLS.
[CHAP. IX.]
CONSTITUENTS OF COAL.—PROCESS OF COMBUSTION.—HEAT EVOLVED IN IT.—FORM AND STRUCTURE OF BOILER.—WAGGON BOILER.—FURNACE.—METHOD OF FEEDING IT.—COMBUSTION OF GAS IN FLUES.—CONSTRUCTION OF GRATE AND ASH-PIT.—MAGNITUDE OF HEATING SURFACE OF BOILER.—STEAM-SPACE AND WATER-SPACE IN BOILER.—POSITION OF FLUES.—METHOD OF FEEDING BOILER.—LEVEL GAUGES.—SELF-REGULATING FEEDERS.—STEAM-GAUGE.—BAROMETER-GAUGE.— INDICATOR.—COUNTER.—SAFETY-VALVE.—FUSIBLE PLUGS.—SELF-REGULATING DAMPER.—SELF-REGULATING FURNACE.—POWER AND DUTY OF ENGINES.—HORSE-POWER OF STEAM ENGINES.—EVAPORATION PROPORTIONAL TO HORSE-POWER.—SOURCES OF LOSS OF POWER.—ABSENCE OF GOOD PRACTICAL RULES FOR POWER.—COMMON RULES FOLLOWED BY ENGINE MAKERS.—DUTY DISTINGUISHED FROM POWER.—DUTY OF BOILERS.—PROPORTION OF STROKE TO DIAMETER OF CYLINDER.—DUTY OF ENGINES.—CORNISH SYSTEM OF INSPECTION.—ITS GOOD EFFECTS.—HISTORICAL DETAIL OF THE DUTY OF CORNISH ENGINES.
(145.)
(146.)
When carbon is heated to a temperature of about 700° in an atmosphere of pure oxygen, it will combine chemically with that gas, and the product will be the gas called carbonic acid. The volume of carbonic acid produced by this combination, will be exactly equal to that of the oxygen combined with the carbon, and therefore the weight of a given volume of the gas will be increased by the weight of carbon which enters the combination. It is found that two parts by weight of oxygen combined with three of carbon, form carbonic acid. The weight of the carbonic acid, therefore, produced in the combustion, will be greater than the weight of the oxygen, bulk for bulk, in the proportion of five to two, the volume being the same and the gases being [Pg253] compared at the same temperatures and under equal pressures. In this combination heat is evolved in very large quantities. This effect arises from the heat previously latent in the carbon and oxygen being rendered sensible in the process of combustion. The carbonic acid proceeding from the combustion is by such means raised to a very high temperature, and the carbon during the process acquires a heat so intense as to become luminous; no flame, however, is produced.