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COPPER AND IRON IN SALT WATER. 195. 
One can hardly form an idea of the slight space which it is sufficient to give to 
the zine and to the iron in order to produce on the metals which they are pro- 
tecting the effects we have just mentioned; thus the quantity of metal needed 
to protect the iron of an armed vessel becomes insignificant. 
The protecting alloys of zine and copper, of zine and lead, &c., act, in pro- 
* portion to the more oxidable metal which enters into their composition, with 
certain conditions of hardness, to which regard is to be paid. With an alloy 
of copper and zinc, the protecting power diminishes, according as this last metal 
is oxidized and carried off, when there remains finally nothing but a copper 
sponge, which is soon changed into oxychloride; the greater the hardness of 
the alloy the slower the production of the effects here mentioned. 
The experiments of which the principal results have been stated had to be 
repeated in the open sea. The minister of marine, fully appreciating their im- 
portance, was kind enough to put at my disposal in the harbor of 'Toulon all 
the necessary means for making these experiments. I cannot sufficiently thank 
him, as well as M. Dupuy de Léme, the latter particularly, on account of the 
useful information which he so kindly furnished me in respect to what con- 
cerns the applications of my experiments. I also thank MM. the naval engi- 
neers for their co-operation, and M. de Mouy, sub-engineer, who, having followed 
my experiments with attention, will be able to repeat them. The experiments 
have been made on a large scale and have not left any doubt as to the accuracy 
of the results obtained in the laboratory, and have enabled me moreover to 
make new observations, which are of interest in applying the experiments. I must 
mention here some observations which ought to be taken into consideration. 
Whenever the iron plating is covered with several coats of red lead, it is 
preserved as long as the paint lasts; but as soon as it is partially removed, 
either by friction or by the dissolving action of the sea, which is slow, the 
metal begins to be attacked at different places; those parts which have lost paint 
are negatived relatively to those which preserve less of it, or none at all; so that 
these last suffer more than the others. rom the above causes spring those local 
changes seattered occasionally over the surface of the plating, which will be easily 
avoided by the employment of protectors, disposed according to principles here 
laid down—protectors which will not come into use until the paint is carried off. 
The copper sheathing of the bottom which is not painted, being in the same 
condition as that of the old vessels, will be exposed to the same disadvantages, 
unless it be protected not only with a view to its preservation, but still more 
for preventing deposits of earths and other matters, which seem to favor deposits 
of shells, mollusks, and marine plants, which it is said do not occur as long as 
the surface continues bright. 
All the parts constituting the sheathing and the armor have been so well ad- 
justed by M. Dupuy de Lome, that it will be quite easy without disturbing 
anything to apply the protectors in such a manner as to clean the former or 
change them as need be. 
It will even be possible, when the vessel is on the point of leaving the basin 
to enter the harbor, with the aid of apparatus I constructed for this purpose, to 
see if all metallic parts are completely protected, or in case they are not, to 
discover the amount of change. ; 
Such are the general results arrived at during the long investigations con- 
ducted either in the laboratory or in sea water upon the means to be used for 
preserving the metals employed for the plating and sheathing of iron-clads, and 
for preventing deposits of shells and other marine bodies. . 
It is quite impossible for me in this extract to enter into details concerning 
the measures to be taken for the preservation of metals, an account of which 
is given in this memoir; it is sufficient for me to say, that the general principles 
appear to be well established, and that the only questions still waiting their 
solution are those which relate to the application of these principles in detail. 
