Portable Agricultural Steam Engines at Newcastle. 713 
from Table III. page 724, was equivalent to the evaporation of 
2162 '5 lbs. of water from and at 212°, hence the heat absorbed 
= 2162-5 lbs. X 966-6 units = 2,090,300. 
No. 8. — The heat lost by radiation and convection from the 
engine during the 263 minutes which the run lasted, to which 
must be added 3 minutes occupied in drawing the fire after the 
preliminary run, and relighting it, so that the total time of 
cooling must be taken as 266 minutes, or 4*433 hours. 
From Table VIII. page 728, we find that the rate of cooling 
was 43,688 units per hour, hence the total loss was 43,688 u. X 
4*433 h. = 193,670 units. The smoke-box of the boiler was un- 
lagged, and during the run was very much hotter than while the 
engine was cooling, and would have a correspondingly increased 
influence on the temperature of the products of combustion, which 
were measured in the upper part of the smoke-box. Sup- 
posing the difference of temperature between the air and the 
surface of the iron to have averaged 315°, and taking the tem- 
perature of the air at 70', the quantity of heat emitted by radia- 
tion and convection, calculated by the formula of Dulong and 
Petit, would amount to 1096 units per square foot per hour. 
The area exposed was about 16 square feet, hence the total 
loss would be 16 squ. ft. x 1096 u. x 4-433 h. = 77,737 u., 
which, added to the quantity already ascertained, makes the loss 
come to 271,307 units. 
Xo. 9. Lastly, the heat lost in ashes, and in the unconsumed 
;uel left on the grate at the end of the trial. 
The weight of ash left by the wood ana coal should, accord' 
ing to the analysis, have been : — 
Firewood, 10-92 lb. x -OlGo = -18 lb. 
Coal, 193 lb. X -0317 = .. .. .. 6-12,, 
^ C-30 „ 
The actual amount of ash weighed back was 10 lb., so that 
5-7 of unconsumed matter at a red-heat remained. This was 
irobably in the form of carbon, as the more volatile portions 
lad most likely been driven off. Assume SOO'' as the average 
emperature of the ash, the heat remaining would be — 
\ 10 lbs. X 430° X -238 = 102 units. 
3-70 lbs. X 14,544 u.= 53,813 „ 
53,915 „ 
Collecting all these figures, we arrange them in the form of 
he following balance-sheet : — 
