712 Report of the Consulting Engineers on the Trials of 
per square foot ; and the corresponding heat-units are found by 
dividing bj Joule's equivalent, 772 ; therefore 
.T, , , , , , 19,471 c. ft. X 2117 lbs. „^ , . 
the heat absorbed = — = 53,394 units. 
No. G. — Heat lost in heating excess of air admitted to the fur- 
nace, and in the displacing of the atmosphere thereby. Mr. Stead's 
analyses show that 23 '45 lbs. of air per pound of coal wereactually 
passed in, being an excess of 12 '07 lbs. The air that passed in 
while the wood was burning was not measured, but as the grate 
was very bare most of the time, it is probable that at least three 
times the proper quantity found its way through the furnace ; 
this would make 12 lbs. excess, so the total weight of excess air 
would be 
10-92 lbs. X 12 lbs. + 193 lbs. X 12-07 = 2460-5 lbs., 
volume at 70- 2460-5 lbs. X 12-387 c. ft. X 530° ^3^^333 ^ ^^^ 
volume at 385== 2460- 5 lbs, x 12 -387 c. ft. x 84 5 ^ ^ 
492 
the volume therefore had expanded by 19,513 c. ft., and the 
heat expended in pushing aside the air must have been 
19,513 c. ft. X 2117 lbs. .orna 
= — ^p:^ = 53,509 units. 
This air was also heated from 70" to 385° or 315°, therefore the 
heat expended in this manner would be 
= 2460-5 lbs. X 315° x -169 = 130,980 units, 
making the total loss of heat by the excess of air admitted 
amount to 184,489 units. We have divided the heat expended 
in this case into two items, namely that converted into the 
work of pushing aside the atmosphere and that actually required 
to heat the air ; but the total heat expended may be ^arrived at 
directly by multiplying the weight ot air heated by the number 
of degrees to which the temperature had been raised, and by 
the so-called specific heat of air at constant pressure, which is 
•238. According to this method the heat expended 
= 2460-5 lb. X 315° X '238 = 184,460 units, 
which agrees very closely with the former calculations. 
No. 7. — The most important work done by the heat generated 
in the furnace was the conversion of the water in the boiler into 
steam at 95 lbs. pressure above atmosphere, This we find 
