ON THE ALLOYS OF COPPER AND ZINC. 91 
ing it into cold water, while alloys containing either more or less than 60 per cent 
of copper are liable to assume different structures, according as they are cooled 
with greater or less rapidity. Two ingots are therefore sometimes cast, on each 
trial of the alloy, one of which is cooled in water and the other in air, for uc. 
This double test is, however, deemed superfluous by skilful workmen. 
I may remark, in this connection, that I have repeatedly obtained crystals, by the 
method of partial cooling, from portions of melted yellow-metal taken from the founder's 
pots at the moment it had afforded them a satisfactory test. These crystals are in no 
wise different from those obtained by myself from alloys of almost identical composition. 
Although, as has been stated, the tendency to form fibres seems to have ceased 
at the alloy containing 60 per cent of copper, I cannot but think that the limit 
of its influence is less clearly defined than the “test” of yellow-metal founders would 
seem to indicate. In the circumstances under which this test is applied, it is doubtless 
true that no fibres are formed; but it is a matter of experience with manufacturers of 
yellow-metal, that the texture of the large ingots from which the sheets of sheathing 
are rolled is no longer so homogeneous as that of the small test ingot; they affirm 
also that this texture may vary greatly, according to the conditions in which the 
ingot is allowed to cool It is evident, therefore, that during the processes of hot 
and cold rolling, and of annealing, to which the alloy is subsequently subjected, its 
texture may undergo various changes; while it is certain that the comparative dura- 
bility of the sheathing, when exposed to the action of sea-water, must in great measure 
depend upon its relative compactness. If it be open and porous, as would be the 
case if a trace of the fibrous structure were present, it is clear that the sheathing 
would soon be destroyed; — not only because the salt water would come in contact 
with its interior portions, but also since the individual crystalline fibres of the 
alloy would doubtless resist its action more completely than the amorphous matter 
attached to them or contained in their interstices; from this a galvanic action 
would be produced, which could not fail to promote the corrosion of the alloy. 
One of the most common complaints against yellow-metal arises from a tendency 
which some specimens of it exhibit to become so friable, after an exposure of 
longer or shorter duration to sea-water, that the sheets may readily be broken 
in pieces, sometimes even between the fingers. Attention has recently been called to 
this subject by Bobierre,* who would refer such cases more particularly to chemical 
* Theses présentées à la Faculté des Sciences de Paris. 
Thèse de Physique: Des Phénomènes électro-chimiques qui caractérisent l'Altération, à la Mer, des 
Alliages employés pour doubler les Navires. Nantes: Imp. Busseuil. 1858. p. 61. 
