320 
MINUTES OF PROCEEDINGS OF 
ON 
A CURIOUS INSTANCE OF ELECTROLYTIC ACTION. 
BY F. A. ABEL, F.E.S. 
[COMMUNICATED BY THE SECRETARY, R.A.I.] 
The inspection of a number of the lead-coated projectiles, employed with 
the Armstrong guns, has recently brought to light some curious and quite 
unexpected instances of the establishment of voltaic action within the coatings 
of certain of these projectiles, and in positions where the existence of an 
exciting cause was not at all anticipated. 
It has been customary to attach the coating of soft-metal (which is an alloy 
of lead with a small proportion of tin or antimony) to the body of the cast- 
iron projectiles, by two different methods. The one consists in providing 
the iron surfaces with a number of grooves formed at somewhat acute angles 
with the surface; the soft metal with which these become filled when it is 
cast over the shot or shell, serves to attach the coating firmly to the body. 
The other method consists in first alloying and coating the surface of iron 
with zinc (by the so-called galvanizing process), and then immediately cover¬ 
ing it with the soft metal. The covering of zinc fixed, in this instance, upon 
the iron, becomes the medium by which the coating of lead-alloy is attached 
to the body of the projectile. By the latter method, therefore, a perfect 
juncture is accomplished between the two parts, while, by that first-named, 
they may be said to be fitted together accurately, or riveted together. 
The different manner in which the iron and the lead-alloy are affected by 
considerable changes of temperature has led, in a few instances, of a very 
special character, to a distortion of the coatings which have been attached by 
the mechanical method (i.e. by means of grooves) in consequence of their 
partial separation from the body of the projectiles. The alterations in form 
presented by some shells of this class, which have been exposed for a time to 
the effects of considerable changes of temperature, differ, however, altogether 
from those exhibited by a small proportion, among a number inspected, of 
shells, the lead-coatings of which were attached by means of zinc. On 
various parts of these shells, the soft metal was found to have become raised 
in the form of blisters, varying in size from J inch to 1 inch in diameter. 
A large (110-pr.) shell, which had been preserved officially, as a standard 
pattern, since November, 1861 (having been kept in a glass case), exhibited, 
upon its coated surface, in addition to numerous smaller blisters, one 
measuring IT inch in diameter, and projecting J inch beyond the surface of 
the shell (see fig). These projections, or blisters, were not confined to any par¬ 
ticular position upon the different shells ; neither had those projectiles, which 
exhibited them, been exposed to any considerable changes of temperature. 
The only inference deducible from the appearance of these projectiles was, 
that the blisters had been produced in consequence of the generation of gas at 
those parts of the shells between the iron surface and the coating of soft 
metal, which gas had gradually accumulated to such an extent as to be placed 
under very considerable pressure, and, consequently, to exert, eventually, an 
amount of force sufficiently great to tear asunder the two surfaces of metal 
which had been joined by means of the zinc, and to raise up and expand the 
