22 MR. JOHN GRAHAM ON CONSUMPTION 
end to end, (a construction of boiler which greatly recom- 
mends itself for strength, durability, compactness, and 
simplicity of form,) working with an excellent draught, and 
under a pressure of 57 lbs. on the inch, I received a con- 
firmation of the importance of disturbing causes. Both 
boilers were reported to me to be precisely the same, but 
that one yielded from the same weight of coals in the 
same time about one-third less steam than the other. 
However, it turned out that there were two slight differ- 
ences. 
The duration of the experiments, the quantity of coals 
consumed, and the draught, were the same for each boiler. 
No. 1. 7ft. diameter, 34ft. long, plates 3S of an inch thick. 
No. 2. Do. do. do. 
No. 1. Surface of fire-bars, 2ft. 8in. by 5ft. 6in. = 14.6 sq. ft. 
No. 2. Do. 3ft. by 6ft. = 18.0 sq. ft. 
No. 1. Evaporated 6.36 lbs. of water per pound of coal. 
No. 2. Do: 8.00 Ibs. do. do. 
No. 1 was then opened and found to be dirty and slightly 
scaled, No. 2 being clean. On No. 1 being thoroughly 
cleaned and again experimented upon a higher result was 
obtained, thus: 
No. 1 evaporated 7.39 lbs. of water per pound of coal. 
I could discover no other disturbing cause to account 
for the small yield from No. 1 beyond the comparative 
smallness of its fire-places, and accompaniment of dirt and 
slight scale. The evaporation is computed from water at 
the boil. 
VIL. Series of Experiments. 
The boiler next experimented with was of the form as 
shown in the drawing usually called James Watt’s “ wag- 
gon-shaped boiler.” It was 26 feet 6 inches long by 6 feet 
6 inches in diameter. 
Fire-place 5 feet 6 inches by 6 feet, equal to 33 square 
feet of fire surface. 
