14 REPORT—1843. 
large engineering structures, iron bridges, viaducts, &c., in place of the perish- 
able “best white lead” paint usually prescribed by the engineer’s specification. 
329. Since the publication of the previous Reports much attention has 
been excited by the new method of zinking patented by Messrs. Elkington 
and M. Ruolz, as connected with their gilding processes, for which they have 
since received the prize of the French Acadenty. For a complete account 
of their highly important improvements, not merely in gilding or silvering, 
but generally in the means of covering any one metal almost with any other, 
reference must be had to the elaborate report presented to the Institute on 
this subject by M. Dumas. These methods consist partly in the use of cer- 
tain complex metallic solutions varying with the metals engaged, principally 
double chlorides and cyanurets, and partly in using these in connexion with 
the voltaic battery. By these beautiful and economical processes, gold, silver, 
platina, copper; tin, cobalt, nickel and zinc may be precipitated upon the sur- 
face of various metals, and amongst them upon cast iron, wrought iron or 
steel at common temperatures. ' 
The coating formed is very thin and perfectly incapable of giving any 
permanent protection to iron immersed in water or exposed to abrasion, but 
I have no doubt of its capability of preserving completely iron in any of its 
states, in moderately dry air, and to a great extent also when exposed freely 
to the weather. The method possesses the important advantages of being 
applicable to very minute or highly wrought articles in iron, to which zine 
could not be applied in a liquid form by heat without destroying their beauty, 
or rendering them brittle by alloying with the iron all through, and also to 
articles so large and unwieldy that no operation involving a high temperature 
or change of place could conveniently be performed on them. Thus statues 
cast in iron may, by Elkington and Ruolz’s processes, be covered with zine 
standing on their pedestals, and the coating even periodically renewed, there 
being no difficulty in forming around them a stanch vessel to contain the 
required solution. For every work in iron applied to architectural construc- 
tion, and only exposed to atmospheric moisture and not liable to abrasion, 
this method is most suitable} as for cast-iron balustrades or cornices, inter- 
nal cramps and ties in walls, wire for ropes or for suspension-bridges, light- 
ning conductors, iron wire-gauze, &c. But I am corivinced, from the results 
given in this and the preceding Report, that no mere covering of zine alone, 
however laid on, will be completely effective in water, and hence many of the 
applications, to cannon shot for instance, proposed by the report of M. Dumas, 
are such as the invention of Elkington and Ruolz will not answer. It is 
scarcely necessary to repeat, that none of the other known metals, except 
zine, capable of being applied by these methods, are admissible where the 
coated surface is liable to abrasion. Zinc and certain of its alloys protect, 
on two grounds, as a sheathing, liable to be more or less destroyed, and vol- 
taically in proportion to the electric energy deyeloped, and whether the in- 
tegrity of the covering metal be broken or not; but metals electro-negative 
to iron stand in a different predicament. 
Of Iron Ships. 
330. The durability of iron ships has become one of the most important 
questions involved in the present inquiry, from the rapid extension which 
this novel branch of naval architecture has received, and is still receiving. 
Amongst other considerations as to their fitness for distant voyages and their 
economic adoption, is that of their durability in respect to corrosion as com- 
pared with timber-built vessels, their relative liability to “ fouling,” and what 
are the means we possess of preventing or retarding both. If the former, 


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