Fuel and Furnaces
The necessary annual supply of Fuel for heating purposes forms a considerable and very important item in garden expenditure. The bulk of tht used in old-fashioned flues was coal, either as supplies from the pit or mixed with cinders. Since the introduction and general adoption of heating by hot water, coke has become a substitute in most cases where it can be obtained. The use of coal in large boilers woulld soon choke the flues with soot, and this is one important objectio. Various gases are removed with the smoke in the manufacture of coal gas for burning, and the coke which remains contains about two-thirds of carbon, and forms the strongest heating combustible material available in quantity for horticultural purposes. The large pieces and those of medium size are of the best quality; the small, generally termed " breeze," being much inferior, and sold at a lower price. Combustion if first caused by heat, and it increases as the heat becomes more intense. A certain qualtity of Fuel consumed inside a Furnace, transmits the heat evolved by combustion to the boiler, &c., surrounding it, or, if allowed, a great part passes to the chinmey, where it is complely wasted. A draught caused by the opening of the damper and ash-pit door at the same time, is a means whereby much oxygen is admitted to the fire, and a passage opened fo the escape of the ascending heat. This is one of the principal things to avoid by using the damper, so that the greatest possible amount of heat may be utilisedm, with, at the same time, an economical use of Fuel in proportion.