EXTRACT OF A MEMOIR 
ON THE 
PRESERVATION OF COPPER AND IRON IN SALT WATER, 
BY M. BECQUEREL. 
BUREAU OF NAVIGATION, Navy DEPARTMENT, 
8 Washington, Aprtl 20, 1865. 
Dear Sir: The protection of the bottoms of iron vessels from corrosion by sea water, and 
from fouling with animal and vegetable matter, is one of the subjects referred by this Depart- 
ment to the National Academy of Sciences for examination and report. I need not enlarge 
upon its paramount importance. A memoir by M Becquerel, on this subject, in the first 
number of the fifty-ninth volume of the Comptes Rendus, has recently attracted my notice, 
and I think the publication of it in English may be serviceable by calling the attention of 
' professed chemists and other systematic experimentalists to the strictly scientific treatment 
of the question. 
I have the pleasure, therefore, to send you the accompanying translation, which I should 
be happy to see preserved and widely circulated in the pages of your valuable reports. 
I have the honor to be, very respectfully, your obedient servant, 
C. H. DAVIS, 
Rear-Admiral, and Chief of Bureau of Navigation. 
Prof. JoSeEPpH Henry, LL. D., 
Secretary Smithsonian Institution, Washington, D. C. 
Tue preservation of metals at sea, especially of copper and iron, has in our 
time become a vital question on account of the transformation of the navies of 
all nations; a transformation suited to bring about a change in their mutual 
.relations. Since this question falls within the province of the physico-chemical 
sciences, I have considered it my duty to give it particular attention, with 
the hope of adding by my own eflorts some new data in aid of its solution to 
those which we already possess. 
This question presents great difficulties, proceeding from numerous causes 
which contribute to the alteration of metals. All these causes, whether me- 
chanical, physical, or chemical, exercise an influence over chemical action, and 
consequently over the production of electricity, which gives rise to isolated 
voltaic couples. They can only be effectually controlled by the closest investi- 
gation and by contending, so to speak, with each of them singly. 
Finding it impossible to communicate the whole of my labors to the Academy, 
I shall confine myself to laying before it a concise abstract of the principal results 
of my investigations, in order that it may get an idea of their whole scope; but, 
before doing so, I will cite those results which have already been obtained on the 
same subject, and thus make the Academy acquainted with my point of departure. 
In a lecture delivered January 22, 1824, before the Royal Society, ( Annales 
de Chime et de Physique, t. xxvi, p. 24,) Davy informed his audience that 
the rapid change in the copper-sheathing of vessels-of-war, and its unequal 
durability, had excited the particular attention of the lords of the admiralty, 
who employed him to investigate the means of preserving the sheathing; and 
that he immediately undertook a series of researches which led him to the dis- 
covery of an important principle, according to which a metal which is electro- 
positive in salt water, being converted into an electro-negative, is preserved 
from all alteration, at least within certain limits. 
