BOILERS AND PIPES. 



241 



There are other rules laid down for 

 calculating the length of pipe required 

 for heating any extent of hothouses ; but 

 although, perhaps, sufficiently correct for 

 ordinary purposes, they are far less scien- 

 tific than those already noticed. Thus, 

 for example, for a hothouse to be heated 

 to about 60°, divide the cubic contents of 

 the space to be heated by 30; when 70° 

 to 75° of heat is required, divide by 20; 

 and when 75° to 80°, by 18— the quotient 

 will give the length of 4-inch pipe re- 

 quired. If 3-inch pipes are used, add 

 one-third ; if 2-inch pipes, double the 

 length of the 4-inch pipe. 



The foregoing calculations, &c, have 

 been made, presuming the buildings are 

 of the ordinary construction, and neither 

 buried underground nor subject to exces- 

 sive damp. If buried much under the sur- 

 face, unless great precautions have been 

 taken to keep the walls dry, much heat will 

 be lost by abstraction ; and, if the walls are 

 damp, a great deal of the heat is lost in 

 evaporating the moisture ; for it has 

 been ascertained that it will take as much 

 heat to vaporise one gallon of water from 

 the walls of a building as would raise the 

 temperature of 47,840 cubic feet of air 

 1°. Pits and hothouses, which may be 

 seldom heated, and then, perhaps, only 

 in the time of frost or wet weather, 

 will take a much longer time to heat 

 than those that are constantly in opera- 

 tion. 



The following calculations have been 

 made by Mr Forsyth as to the propor- 

 tions the surface of pipe should bear to 

 the cubic contents of air to be heated. 

 He says, "I consider 1 square foot of 

 pipe" to 10 cubic feet of air to be heated 

 "necessary for pines; 1 foot in 12 for 

 grapes; 1 foot in 15 for peaches; and 

 1 foot in 24 to keep the frost from green- 

 house plants, when the thermometer in 

 the open air falls to zero." 



The following are the calculations of 

 Mr Scott, the intelligent superintendent 

 of the gardens at Leigh Park, Hants, re- 

 garding the proportion of hot-water piping 

 to heat certain capacities : " In stoves of 

 considerable dimensions, containing from 

 50,000 to 60,000 cubic feet of air, having 

 a surface of glass (including rafters and 

 sash bars) in the proportion of 1 square 

 foot of glass to 10 cubic feet of air, the 

 proportion of 1 foot of 4-inch pipe to 5.33 



VOL. I. 



feet of glass will be ample heating surface 

 to maintain a minimum temperature of 

 60° during severe weather. But in a 

 house containing from 10,000 to 15,000 

 cubic feet of air, with a surface of glass 

 in the proportion of 1 foot of glass to 

 6.75 feet of air, the proportion of 1 foot 

 of pipe to 3 feet of glass will be required 

 to maintain a minimum temperature of 

 60° or 65°, provided covering be not used. 

 In vineries and peach-houses the quan- 

 tity of heating surface required will 

 very much depend on circumstances, as 

 whether they are detached or connected 

 in a range, also whether the crop is 

 wanted early or late ; but 1 foot of pipe 

 to 4 feet of glass will be a fair average for 

 vineries, and 1 foot of pipe to 5 feet of 

 glass for peach-houses. Conservatories 

 and greenhouses, according to size and 

 other circumstances, will require 1 foot 

 of 4-inch pipe to 5 or 6 feet of glass. 

 If flues be preferred, I should consider 

 1 foot of an ordinary flue equal to 2 feet 

 of a 4-inch pipe. In pits or small forcing- 

 houses, where covering can be easily 

 applied at night, the proportion of 1 foot 

 of pipe to 4 or 5 feet of glass will main- 

 tain a minimum temperature of 60°." — 

 Journal of Horticultural Society. 



Pipes used for hothouse purposes should 

 be made of what is called hard cast-iron, 

 as it resists oxidation nearly three times 

 as long as soft or common cast-iron, and 

 fully as long as wrought iron does. The 

 latter is seldom or never used for pipes, 

 but for boilers it frequently is. Galvan- 

 ised hard cast-iron pipes would be a great 

 improvement. 



To prevent oxidation is a most impor- 

 tant matter, as it not only in time destroys 

 the pipes, but it prevents the radiation of 

 heat from them. Many experiments 

 have been tried with a view to this, but 

 with no very satisfactory result. It is 

 probably the best way to keep the sur- 

 face of the pipes always clean by a free 

 use of pumice stone. To paint pipes 

 with lead paint, although it is often done, 

 appears to be injurious, as it prevents the 

 free radiation of heat; and Hood conjec- 

 tures this to arise " from the total change 

 of state which the lead undergoes by its 

 chemical combination with the carbonic 

 acid in the process of making it into white 

 lead. Practically," he continues, "it is 

 found to have an injurious tendencv on 



2 H 



