THE EOYAL ARTILLERY INSTITUTION. 
321 
comparatively plastic al¬ 
loy of lead. This influ¬ 
ence was fully borne out 
by the following results 
of examination of the 
blisters. 
When these were punc¬ 
tured, under water, a 
quantity of gas, exist¬ 
ing evidently under con¬ 
siderable pressure, made 
its escape. The gas was 
separately collected from 
blisters upon different 
shells, and was found, 
in all instances, to con¬ 
sist of pure hydrogen. 
The entire volume of 
gas, enclosed in the large 
blister Specially referred 
to above, was carefully 
collected, and its volume 
was determined. The 
capacity of the blister 
was afterwards measured, 
and the results furnished 
by these determinations showed that the hydrogen existed at the period of 
examination, under a pressure very slightly exceeding ten atmospheres. 
By carefully cutting through the metal surrounding the blisters, several, 
which had been otherwise operated upon, were removed from the shells, 
the internal surfaces remaining untouched. On a close inspection of these 
surfaces, they were all found to resemble each other closely, those of the 
blisters as well as those of the iron body of the shell, immediately beneath 
them. They presented a frosted metallic appearance, small dark patches or 
spots, indicative of corrosion, being visible here and there. Those of the 
blisters and of the iron beneath were alike coated with zinc, and their pe¬ 
culiar appearance, just referred to, was to be ascribed to the existence, upon 
them, of numerous small projections, such as are observed upon the surfaces 
laid bare when a piece of metal is fractured by a tensile strain. 
It is evident, from the foregoing details, that the projections, or blisters, 
which have been described, had been produced by the gradual disengagement 
of hydrogen between the body of the projectile and the coating of lead-alloy, 
whereby the two descriptions of metal, joined together thoroughly in the first 
instance (except probably at a few minute points) through the medium of 
zinc, had been torn asunder, and the thin intermediate zinc coating itself 
divided, the gas gradually creating further space for itself by expanding the 
envelope of soft metal which confined it. 
That these results must have been due to the electrolytic decomposition of 
some hydrogen-compound, which had become enclosed between the metals, 
is self-evident; an examination into the process of manufactures of these 
projectiles, aided by a few simple experimental data, appears to leave no doubt 
regarding the primary cause of this disengagement of gas. 
The operations included in the system of coating the iron projectiles by 
