322 
MINUTES OF PROCEEDINGS OF 
the aid of the so-called galvanizing process; are as follow :—The cast-iron 
projectile, after having been turned, so as to present a perfectly clean metallic 
surface, is heated in an oven until its temperature approaches the fusing 
point of zinc; it is then plunged into a solution of sal-ammoniac, almost 
immediately withdrawn, and immersed in a bath of melted zinc, where it re¬ 
mains for about two minutes, when it is transferred to a bath of the lead-alloy 
with which it is to be coated. After remaining in this bath also for a period 
of two minutes, it is withdrawn and placed in a mould. The projectile thus 
treated has become uniformly covered with a thin coating of soft metal, the 
thickness of which is afterwards increased, by pouring a further quantity of 
the alloy round the coated projectile, directly it has been placed in the mould. 
When the heated projectile is passed from the chloride of ammonium 
solution to the bath of zinc, portions of the salt remain adhering to the iron, 
upon its immersion in the zinc, and there is no doubt that a small proportion 
of water may also, occasionally, be carried along with it, so as to be brought 
together with it into contact with the melted metal. A small proportion of 
chloride of zinc is always formed at this stage of the process, by decomposi¬ 
tion of the chloride of ammonium, in consequence of the high temperature 
at which particles of this salt are brought into contact with the zinc, and with 
oxide of zinc, small portions of which may accidently attach themselves, at the 
moment of immersion, to any slight inequalities on the surface of the iron. 
The remarkable tendency of chloride of zinc to absorb and retain water, even at 
very high temperatures (the latter being only gradually expelled from it, even 
at the temperature of melted zinc), renders it easily conceivable that, at the 
time of production of the zinc-salt, any water accidentally present, besides 
that which results from the decomposition of the'ammonium-salt by oxide of 
zinc, will at once be absorbed by it; there is no doubt, therefore, that any 
particles of chloride of zinc accidentally enclosed by the zinc-coating formed 
upon the iron surface, will still retain some water at the expiration of the 
brief period during which they continue exposed to the high temperature of 
the zinc-bath. Afterwards, when the coating of zinc becomes, in its turn, 
speedily enveloped in that of the lead-alloy, the temperature of the projectile 
gradually diminishing up to the termination of the process, the escape, or 
decomposition, of the water, through the agency of heat, is speedily arrested. 
Thus it is that portions of water become accidentally enclosed between the 
iron body and the zinc-coating of compound projectiles prepared by this 
system; and it is this enclosed water which afterwards suffers gradual decom¬ 
position through electrolytic agency; the accumulation of the liberated 
hydrogen giving rise, eventually, to the projections or blisters in the coating 
of soft metal. 
The surfaces laid bare by carefully cutting open many of these blisters, in¬ 
variably furnished proof that chloride of zinc had been enclosed at those places, 
and that a basic chloride had been formed. Water removed from them a mere 
trace of chlorine, but, by a brief treatment with dilute acetic acid, abundant 
evidence was obtained of the existence of a chloride within the blisters. 
It should be observed that these accidental distortions of the lead-coating 
on Armstrong projectiles which have been prepared by means of the gal¬ 
vanizing process, appear not to be of frequent occurrence, and that they do not 
interfere with the efficiency of such projectiles, because, even in the most 
striking instances, they constitute only a very small proportion of the coating 
of soft metal, which is, in all other parts, inseparably joined to the iron; 
and also, because the coating may, in places where it has been raised in 
blisters, be restored to its original dimensions by simple mechanical means. 
