578 Application of Hot Water in Heating Hot-houses. 



15. Now the heat given off by the surfaces of the apparatus 

 depends on the kind of materials they consist of, and their 

 temperatures. The following Table shows the boiling point 

 and temperature of the heating surface for different liquids 

 when confined by iron or glass ; also their specific heat, or that 

 quantity of heat they can convey when that conveyed by an 

 equal volume of water is unity. 



Water 

 Sea Water 

 Brine 



Water 48, Alum 52 

 ■ 55, Sulphate c 



Petroleum 

 Linseed Oil . 

 Sulphuric Acid 



16. If the cubic feet of air to be heated per minute be 

 multiplied by the number of degrees it is to be warmed, and 

 the result be divided by twice the difference between the 

 temperature of the house, and that of the surface of the pipes, 

 the result will be the feet of surface of iron pipe, &c. required. 

 Thus, if 1000 cubic feet per minute are to be warmed, and the 

 extreme case is supposed 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 190° when 

 the water boils,* but only 180° in the average state, therefore, 

 ol?^ X 3 ^ = = 116 feet of surface. 



* The mean and extreme temperatures for the neighbourhood of London may 

 be obtained from the observations of Mr. Daniell, in his Meteorological Essays. 



