■ 694 Bejjort of the Consulthg Evgineers on the Trials of 
In the case under consideration, the water was pumped in at 
83-6°, or 128-4° below 212'; hence 128*4 units of heat have to 
be added to 966*6, making 1095 units in all, and the quantity 
of water which would have been evaporated, had it been 
supplied at 212', would be increased in the proportion of 1095 
to 966-6, that is i^^^^^^^^f^^^^^ = 1630-8 lbs. Divid. 
ing this quantity by the 138-25 lbs. of coal used, we have, omit- 
tlfeig for the moment the jacket question, the evaporative power of 
the boiler represented by 11 • 79 lbs. of water from and at 212° 
per 1 lb. of coal. 
With respect to the jacket question, the indicated horse-power 
developed was 13-88, consequently the units of heat converted 
13-88 H.p. X 33,000 foot-lbs. 
into work per minute were = 772^ ~ 
593 • 3 units. The steam in the boiler and jackets was at 120 lbs. 
pressure per square inch, and therefore at 350' temperature above 
zero Fahr., and the number of units of heat per 1 lb. of steam 
condensed at the same temperature would be 870*9. The run 
lasted 263i^ minutes, hence the total quantity of steam condensed 
593 - 3 units X 263-5 minutes . 
in the lackets was = ^ = 1 < 9 - 0 lbs. 
870-9 units 
But this quantity must also be reduced to the standard tem- 
perature and pressure, and since it requires only 870-9 units to 
convert water at 350' into steam at 120 lbs. pressure, while it 
needs 966-6 units to evaporate from and at 212', it follows that 
179 - 5 lbs. must be reduced in the ratio of 870 - 9 to 966 • 6, which 
makes it 161-7 lbs. The utmost that the boiler evaporated, 
therefore, was 1630-8 lbs. + 161-7 lbs., or 1792-5 lbs. from 
and at 212° by the combustion of 138-25 lbs. of coal, being at 
the rate of 12-96 lbs. of water to 1 lb. of coal. 
Table III., on page 724, exhibits the results of the calcula- 
tions relating to ten out of the eleven engines tried. 
Efficiency of Boilers and Engines — Trials on the Brake. 
The brakes used were the same as those which werfe employed 
at Cardiff. They were very carefully adjusted, and the brake- 
straps were accurately balanced when in the position they 
would occupy while running. It was decided to apply at 
these trials a correction for the friction of the brakes them- 
selves and of their coupling shafts, a refinement which had 
never before been attempted. A rough approximation to the 
needed allowance was made before the trials by ascertaining 
what weight hung on the periphery of the brake-wheels would 
make them revolve slowly ; but after the trials were over. 
