510 transactions of the american institute. 



American Institute, Polytechnic Association, ) 

 JVovemher 8, 1860. \ 



Mr. John Johnson in the chair. 



Mr. G. H. Babcock, in answer to some questions which were 

 put to him at the previous meeting in regard to the relative 

 economy of air and steam, submitted the following as the result 

 of his calculations : 



The combustion of one pound of coal will heat 60 lbs. of wa- 

 ter from 32 deg. to 212 deg.=180 deg. 



The specific heat of air being quarter that of water, one lb. of 

 coal will heat 240 lbs. of air 180 deg., or 84 lbs. 508 deg., which 

 is sufficient to double its pressure, the initial temperature being 

 60 deg. F. 



84 lbs. of air= 1,102 cubic feet at 15 lbs. pressure, or 110 cu- 

 bic feet at 150 lbs., one pound of coal will then produce 110 cu- 

 bic feet expansion of air, varying from 300 lbs., to 150 lbs. pres- 

 sure =208 lbs. average, 110 cubic feet = It, 280 square inches, 

 -fll feet. 



l7,280 + (208-150) + ll=ll,024,640 feet, lbs=the mechanical 

 effect of one pound of coal applied to heat air at 150 lbs. 



Deducting 50 per cent, loss in furnace — steam boilers average 

 about 35 per cent. — we have left 5,512,320 ft. pounds. 



Add 50 per cent, gain by use of economizer, and we have 

 8,268,480 ft. pounds. 



Allowing 50 per cent, of this to be lost in the engine by fric- 

 tion, lost space, &c., and we shall have a practical effect of 4,134,- 

 240 foot pounds from one pound of coal, which is equal to 48 

 pounds of coal per hour per horse power. 



Utmost capacity of the Cornish engine, 1.48 lbs. per hour per 

 horse power. 



Common duty of Cornish engine, 1.98 lbs. per hour per horse 

 power. 



Average duty of Cornish engine, 2.64 lbs. per hour per horse 

 power. 



Average duty best Marine engine, 4.4 lbs. per hour per horse 

 power. 



A high pressure air engine properly constructed, should, there- 

 fore, run for 25 per cent, of tliB fuel used in the best Cornish en- 

 gine, or 11 per cent, of that used in the best Marine engines. 



Mr. Seely. — Has the regenerator and economizer been left out 

 in any of these Wilcox engines ? 



