ON THE ALLOYS OF COPPER AND ZINC. 41 
found that satisfactory tests cannot be obtained, the copper is immediately rejected 
by the founders, and applied to some other use. No similar means of controlling 
the purity of the brass in question are known. 
It does not appear—at all events it has never been proved — that any serious 
injury results in practice from the use of the most varied kinds of copper, so 
long as they afford the desired homogeneous alloy containing 40 per cent of zinc. 
I do not wish to deny that hurtful impurities may at times occur in yellow-metal, 
in spite of the test to which I have so frequently alluded. Most probably the 
very rare cases in which this alloy wears out irregularly, portions of the sheet 
being much corroded, while other parts are scarcely at all acted upon and have 
preserved their original color and malleability, may be referred to the irregular 
diffusion of such impurities throughout the mass of alloy of which the sheet 
was formed;* but their influence must be regarded as being of very slight im- 
portance in comparison with the changes of structure which have already been dis- 
cussed. 
The following is a list of the alloys which I have prepared. Crystals were 
obtained from all of them, with the exception perhaps of one or two of those lowest 
in the series, where the tendency to assume a pasty state during solidification renders 
the crystallization obscure. | 
The amount of copper contained in both the crystals and the portion of fluid 
alloy poured off from above them was determined directly by assay in each instance. 
The copper used in the preparation of the alloys was a very pure article from 
Lake Superior; it contained only a certain amount of suboxide of copper and 
traces of silver. : 
The zinc was from La Vieille Montaigne, containing as its principal impu- 
rity a small amount of lead. -Both metals were granulated for convenience 
in weighing. The lead and other impurities have been neglected in stating my 
results. 
-* Tt is not impossible that the small amount of silver which, as is well known, is precipitated from 
sea-water upon the metallic sheathing of ships, can accumulate to such an extent in yellow-metal which 
has been repeatedly used and remelted, that the durability of the latter may be seriously impaired thereby. 
It is, however, equally probable, and perhaps more so, that the greater part of this silver is eliminated 
in the preparation of the alloy, when the old metal is fused with zinc. 
VOL. VIII. 6 
