BOILERS AND PIPES. 



239 



At At 

 -2850 = WX; ° r > 2850i = W== 

 the quantity of water in cubic feet that 

 must flow along the pipe per minute to 

 supply the heat ; and the quantity being 

 equal to the velocity per minute multi- 

 plied by the area of the pipe, the means 

 of knowing whether the pipes be capable 

 of allowing the proper quantity to flow 

 along or not becomes easy ; as well as 

 fixing the proper diameter. If any other 

 liquid be used, the number 2850 should 

 be multiplied by the specific heat of that 

 liquid ; and then proceed as before. 



" The least quantity of liquid the appa- 

 ratus could contain is double the quan- 

 tity cooled during the time of making 

 one circuit in the pipes, which is found 

 by dividing the quantity w, as found 

 above by the number of circuits, or parts of 

 a "circuit, made in a minute, and com- 

 paring the velocity with the length of 

 the pipes. Whatever the quantity is 

 in excess above this is to be considered a 

 reserve of hot fluid to afford heat after 

 the fire is out ; and the fire must be so 

 much earlier lighted as to heat this 

 excess of water, as it must be hot before 

 the surface can afford its effective supply 

 of heat." Small boilers, it appears from 

 the above reasoning, are better for green- 

 houses, and such structures as require to 

 be speedily heated, than large ones ; and 

 moderately large boilers may be the best 

 for pine and other stoves, where a con- 

 stant and high temperature is required — 

 as the larger quantity of water, when 

 once heated, retains its heat longer, and 

 at a comparatively small addition of fuel. 

 It is entirely owing to the excess of fluid 

 that hot water has this advantage over 

 steam heat ; and the knowledge we now 

 have of the heat which water contains, in 

 proportion to its temperature, enables us 

 to calculate the time the cooling of the 

 fluid will maintain the heat of a house. 



Hood, who is excellent authority upon 

 heating, has made the following calcu- 

 lation as to the quantity of pipe required 

 to heat a given space, founding his esti- 

 mate upon computation of the specific 

 heat of gases compared with water. 

 Every substance, it is well known, has its 

 peculiar specific heat. " Now, 1 cubic 

 foot of water, by losing 1° of its heat, 

 will raise the temperature of 2990 cubic 

 feet of dry air the like extent of 1° ; and 



by losing 10° of its heat, it will raise the 

 temperature of 2990 cubic feet of air 10°, 

 or 29,900 cubic feet 1°, and so on." He 

 calculates the quantity of heat lost by 

 radiation, and imperfect fitting of doors 

 and sashes, but makes no allowance for 

 the supposed loss of heat by the laps of 

 the glass in houses, such as plant and 

 pine stoves, where a great degree of 

 humidity is maintained, as the condensed 

 steam running down the inside of the 

 roof fills the spaces between the laps, and 

 prevents the escape of the heated air. 

 The calculation in the quotation above 

 refers only to dry air, such as that of 

 rooms and airy plant-houses, where only 

 a limited quantity of water is employed ; 

 but in such as are much saturated with 

 moisture, the case is somewhat different. 

 Taking the temperature of the latter at 

 60°, the same amount of heat that would 

 have heated 2990 cubic feet of dry air 

 will only raise the temperature of 2967 

 cubic feet of saturated air to the same 

 degree ; because the latter number of 

 feet of saturated air will contain 67 cubic 

 inches of water, which will absorb as 

 much heat before being converted into 

 vapour as would raise the temperature 

 of 115.922 cubic feet of air 1°. This 

 Mr Hood estimates to be equal to the 

 entire heat that 46 feet of 4-inch pipe 

 will give off in ten minutes, when 

 its temperature is 140 degrees above 

 that of the air. " The glass will, how- 

 ever, cool much less of this saturated air, 

 than of dry air, for the mixture of air 

 and vapour has greater specific heat than 

 dry air." In conservatories and forcing- 

 houses, the quantity of air to be warmed 

 per minute must be 1| cubic feet for each 

 square foot of glass which the building- 

 contains. The quantity of air to be 

 heated being ascertained, the requisite 

 length of pipe may be found by the fol- 

 lowing rule : — 



"Multiply 125 by the difference be- 

 tween the temperature at which the 

 [house or] room is proposed to be kept 

 when at its maximum, and the tempera- 

 ture of the external air, and divide this 

 product by the difference between the tem- 

 perature of the pipes, and the proposed 

 temperature of the room [or house] : then, 

 the quotient thus obtained, when multi- 

 plied by the number of cubic feet of air 

 to be warmed per minute, and this pro- 



