By Mr. Thomas Tredgold. 579 



If we employ brine for the same case ; 



theil > 2(m~50 )= 1Q6feet 



And, with oil, 



2(510— so) ~ 32 2 feet would answer the purpose. 

 When bright tinned iron, earthen-ware, &c. are employed for 

 pipes, much more surface is necessary. 



The advantage of using a fluid which bears a high tem- 

 perature without boiling is therefore considerable in reduc- 

 ing the quantity of surface required to produce a given effect; 

 oil requiring only one-third of the surface necessary for water ; 

 but oil is very inflammable, and sulphuric acid corrosive. 



17. It is known from experience that the heat which raises 

 the temperature of one cubic foot of water one degree will 

 heat 2850 cubic feet of air one degree; consequently, if A be 

 the quantity of air to be heated per minute to t degrees, and, 

 x be the difference of the temperature of water in the appa- 

 ratus, then 



£~ == wx ; or, 2 ^ 0x = w = the quantity of water in cubic 

 feet that must flow along the pipe per minute to supply the 

 heat ; and, having shown (Art. 11) how to calculate the velo- 

 city ; and the quantity being equal to the velocity per minute 

 multiplied 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 of fixing the 

 proper diameter. If any other liquor be used the number 

 2850 should be multiplied by the specific heat of that liquib ; 

 and then proceed as before. 



18. The least quantity of liquid the apparatus could 



