144 



HEATING AS APPLIED IN HORTICULTURE. 



That an immense economy of heat may 

 be effected by introducing cold air into a 

 chamber round the sides and over the 

 top of every hothouse furnace, is obvious, 

 as this air will become heated without any 

 extra expenditure of fuel, and may be 

 conveyed to a considerable distance if 

 required. This we have frequently ex- 

 emplified, and very recently upon rather 

 an extensive scale in heating St Mary's 

 Chapel in Dalkeith Park. This beautiful 

 edifice is heated with hot water, and a 

 smoke- consuming furnace placed in a 

 chamber under the vestry. Over the 

 boiler and furnace is formed an air- 

 chamber of fire-bricks, 6 feet by 4, and 

 18 inches high, which is supplied with air 

 by two ventilators, opening into the cellar 

 in which the furnace is placed : as the 

 air becomes heated, it is forced forward 

 into the drains or chambers under the 

 floor in which the hot-water pipes are 

 placed, by the pressure of the cold air 

 from without. This not only throws a 

 constant current of heat into the build- 

 ing, but at the same time equalises the 

 distribution of it, so that it is as warm at 

 one part as at another. Nor is this the 

 only advantage of admitting a supply of 

 air moderately heated in a brick cham- 

 ber. The effects produced on the animal 

 economy by inhaling air which has passed 

 over heated metallic surfaces, such as hot- 

 water pipes, and more especially hot-air 

 stoves or tubes, are sufficiently known. 

 The small particles of animal and vege- 

 table matter which the air always holds 

 in suspension become decomposed, and 

 resolved into their various elementary 

 gases, according to the intensity of heat 

 they are subjected to ; and the hygrome- 

 tric water of the atmosphere is almost 

 entirely decomposed, the oxygen entering 

 into combination with the iron, and the 

 hydrogen mixing with the air. The salu- 

 brity of the air is greatly changed by 

 these operations, and it becomes highly 

 deleterious to animal life. But heat 

 generated in a brick-built chamber, and 

 not brought to too high a temperature, 

 as in the above case, is by no means of so 

 deleterious a character, because the hygro- 

 metric water of the atmosphere is not 

 decomposed, as would be the case if the 

 air was heated to a high temperature in 

 a metallic chamber, or made to pass over 

 a metallic surface such as the top of a 



boiler, the bricks having no affinity for 

 oxygen such as that possessed by heated 

 metal. The top of the boiler in the case 

 above referred to is covered with 2-inch 

 fire-tiles, and, to render the heated air as 

 little hurtful as possible, a shallow vessel 

 of water is placed in the hot-air chamber, 

 which can be supplied through the venti- 

 lators. 



Hood, in his excellent treatise on heat- 

 ing, very properly remarks : "As the power 

 of iron to decompose water increases with 

 the temperature of the iron, the limit to 

 which the temperature of any metallic 

 surface ought to be raised, which is used 

 for radiating heat for the warming of 

 buildings, should not much, if at all, ex- 

 ceed 212°, if the preservation of health is 

 a matter of moment. The importance of 

 this rule cannot be too strongly insisted 

 on. It ought to be the fundamental 

 principle of every plan, for upon it de- 

 pends the wholesomeness of every system 

 of artificial heat." 



As the heat in hot-water pipes rarely 

 exceeds 180° or 200°, the decomposition 

 of water by that heat is immaterial com- 

 pared to that produced by steam, which 

 is seldom under from 220° to 230°, and 

 infinitely less than that by heated air, 

 which frequently has to pass over metal- 

 lic bodies red hot, as is often the case 

 where hot-air stoves are employed. 



Heating by hot water is undoubtedly 

 the most wholesome form yet adopted, 

 and, in its various modifications, it may 

 be applied to all kinds of structures. 

 The temperature it produces is uniform 

 and moderate, when compared with hot- 

 air stoves, flues, or steam. There are a 

 few cases, however, which should be 

 noticed, where heating by hot water would 

 be attended with more expense than is 

 necessary; and these are, small green- 

 houses and nurserymen's plant-houses, 

 where only half hardy plants are kept, and 

 where a well-constructed flue can be in- 

 troduced without occupying useful space. 

 These only require heat sufficient to ex- 

 clude frost, and they might be heated by 

 an Arnott's, White's, or other stove, placed 

 outside the building. In ordinary winters 

 it might not be necessary to use the stove 

 above a dozen times ; and, as frost in gene- 

 ral sets in pretty suddenly, these houses 

 would, by such means, be heated in less 

 time than by a hot-water boiler and pipe. 



