238 



HEATING AS APPLIED IN HORTICULTURE. 



integrating that which had formed pre- 

 viously to its application. And we 

 should be wanting in justice to the in- 

 genious inventor, were we not to state 

 that the invention has been tried for 

 nearly twelve months upon the boilers 

 of the engines printing the Times, work- 

 ing on an average of seventeen hours per 

 diem throughout the year. Not only 

 have the boilers been kept perfectly free 

 from deposit, but an incrustation which 

 had formed previously to the application 

 of the invention has been entirely re- 

 moved. We can further state, that nei- 

 ther the boilers nor any part of the ma- 

 chinery has been in any, even in the 

 slightest degree, acted upon or injured by 

 the action of the remedy in question. 



Pure water is usually employed where- 

 with to charge the boiler and pipes; 

 there are, however, other liquids that may, 



under certain circumstances, be employed, 

 as for example, where a very high tem- 

 perature is required. The advantage of 

 using fluids which will bear a high tem- 

 perature without boiling, consists in re- 

 ducing the quantity of surface necessary 

 to produce a given effect. Thus oil re- 

 quires only one-third of the surface neces- 

 sary for water, and sulphuric acid some- 

 what less. Oil is, however, dangerous, on 

 account of its inflammability; and sul- 

 phuric acid objectionable, as it is so very 

 corrosive. 



The following table, drawn up by 

 Tredgold, shows the boiling point and 

 temperature of the heating surface of 

 different liquids, when confined by iron or 

 glass ; also their specific heat, or that 

 quantity of heat they can convey, that 

 conveyed by an equal volume of water 

 being taken as 1 : — 



Kind of Liquid. 



Specific Heat. 



Boiling 

 Point. 



Greatest 

 Temperature 

 of Surface. 



Average 

 Temperature. 



Water, 



1° 



212o 



190° 



180° 



Sea Water, 





214 



192 



182 



Brine, 





226 



205 



192 



Water 48, alum 52, 





220 



200 



188 



Water 55, sulphate of lime 45, . 





220 



200 



188 



Petroleum, 



.415 



316 



285 



245 



Linseed oil, .... 



.496 



600 



540 



510 



Sulphuric acid, .... 



.35 



605 



544 



514 



Excellent rules have been laid down by 

 both Tredgold and Hood to find out the 

 quantity of pipe necessary to heat a given 

 cubic amount of air. " If the cubic con- 

 tent of air to be heated per minute," says 

 the first of these authorities, "be multiplied 

 by the number of degrees it is to be 

 warmed, and the result be divided by 

 twice the difference between the tempera- 

 ture of the house and that of the surface 

 of the pipes, the result will be the feet of 

 surface of iron pipe required. Thus, if 

 1000 cubic feet per minute are to be 

 warmed, and the extreme case is sup- 

 posed to be that when the external air 

 is 20°, the house should be 50° ; and 

 therefore the air is to be warmed 30° ; — 

 and with water the surface will be 1 90° 

 when the water boils, but only 180° in 

 the average state : therefore 



1000 x 30 



30000 

 260 



116 feet of surface. 



2(180 — 50) 

 If we employ brine for the same case, 

 1000 x 30 



then 



And with oil, 



2(192 — 50) 



1000 x 30 



= 106 feet. 



= 324 feet 



2(510 — 50) 

 would answer the purpose." 



" When bright-tinned iron, earthen- 

 ware, &c, are employed for pipes, much 

 more surface is necessary." 



" It is known from experience that the 

 heat which raises the temperature of 1 

 cubic foot of water 1°, will heat 2850 

 cubic feet of air 1° ; consequently if A be 

 the quantity of air to be heated per 

 minute to t degrees, and x be the differ- 

 ence of the temperature of water in the 

 apparatus, then 



