ON STEAM-BOILER EXPLOSIONS. 687 
other steam at a still lower temperature and pressure; and so on, till the 
temperature is reduced to 212° F., and the pressure to0. Then there remains 
in the boiler a portion of water at the boiling-point, the other portion having 
gone off in the shape of steam of continually diminishing pressure. From 
this it is evident that the destructive energy of the steam, when a certain 
pressure is shown by the steam-gauge, is proportional to the quantity of 
water in the boiler. 
I have long desired to possess myself of some theory and experiments 
which would enable me to form a numerical estimate of the proportion 
between the quantity of water at a given temperature and its destructive 
power. Several years ago I corresponded on this subject with my friend 
Professor W. H. Miller, of Cambridge ; but it appeared difficult then to find 
sufficient materials for a certain conclusion. In the present year I again 
requested him to take up the subject; and I received from him a complete 
theory on the generation of steam in the way which I have described, with 
references to the latest trustworthy experiments bearing on the subject. I 
also received from him references to the experiments of the French General 
Didion, illustrating the power of gunpowder in cannons. About the same 
time, by the kindness of Messrs. Ransomes and Sims, of Ipswich, experiments 
had been made, at my request, by their able engineering superintendent, George 
A. Biddell, Esq., on the quantity of water which does actually escape in steam 
from a boiler in which the pressure has been raised to 60 lbs. per square inch. 
The result of this experiment agreed well with Professor Miller’s theory, 
suggesting only a small correction, which Professor Miller refers, and, I 
doubt not, justly, to the iron of the boiler. From these I have been able to 
obtain a result which I believe to be worthy of every confidence. 
I will first state, as the immediate result of Mr. Biddell’s experiments, 
that when there were, in the boiler of a small locomotive, 22 cubic feet of 
water at the pressure of 60 lbs. per square inch, and the fire was raked out, and 
the steam was allowed gently to escape with perfect security against priming, 
the quantity of water which passed off before the pressure was reduced to 0 
was 2? cubic feet, or one-eighth of the whole. 
In regard to the use made of Professor Miller’s theory, Professor Miller 
had succeeded in obtaining a numerical expression for the pressure of the 
steam at twelve different measures of the volume occupied by water and steam, 
which expression I have succeeded in integrating accurately; and I have 
thus obtained an accurate numerical expression for the destructive energy 
of the steam. In regard to the use of General Didion’s experiments, these 
experiments give the velocity of the ball, in cannon of different sizes, pro- 
duced by different charges of powder. I have found, by trial with the formula 
Wu 
29 x weight of powder 
energy per kilogramme of powder, and have adopted it in the comparison. 
The result is as follows :— 
The destructive energy of one cubic foot of water, at 60 lbs. pressure per 
, Which of these experiments exhibits the greatest 
“square inch, is equal to the destructive energy of two English pounds of 
gunpowder in General Didion’s cannon-experiments. 
General Didion’s experiments were made, as I understand, with smooth- 
bored cannon. It cannot be doubted that much energy is lost in the windage, 
some also from the circumstance that the propelling power ceases at the 
muzzle of the gun before all the energy is expended, and some from the 
coolness of the metal. If we suppose that, from all causes, one-half of the 
energy was lost, then we have this simple result :— 
