. ON THE ALLOYS OF COPPER AND ZINC. ^29 
blue-violet color. Indeed, it would appear as if, by properly regulating the process 
of cooling, a series of colors as varied as those assumed by steel, according to the 
different degrees of heat at which it is tempered, might be obtained. Alloys con- 
taining about 45 per cent of copper exhibit a dull gray coloration on fracture, 
which, combined with their other physical properties, often causes them, when un- 
polished, to resemble, as was remarked by Karsten,* metallic sulphides far more 
.than metals. 
Although the iridescence which I have described is perhaps seen to best ad- 
vantage in the alloy from equal parts of copper and zinc, and may perhaps be 
produced most readily upon it and the neighboring alloys of a fibrous texture, 
it is by no means confined to these. I have noticed beautiful yellow coatings upon 
alloys containing 60, 53, and particularly on the one of 90.77 per cent of copper. It 
may probably occur upon any of the yellow alloys, and is doubtless produced at will 
upon some of them by manufacturers of ornamental brass castings. 
In this connection, it may be mentioned that the color of the oxidized surface of 
the thin sheets of alloy obtained by pouring upon stone varies from a grayish black, 
tinged with blue, in the specimens containing about 90 per cent of copper, to a dirty 
dark yellowish-green, as in the alloy of 65 per cent of copper; and from a dull lead 
color (alloy of 38.5 per cent of copper) nearly to white, in the alloys rich in zinc.t 
Marked changes, not only of color, but also in other of the physical properties of 
some of these alloys, may be produced by varying the conditions in which they pass 
from the liquid to the solid state. These changes are very peculiar, and are evidently 
. of great importance, not only in their practical bearing, but also from affording 
another instance of the phenomena of “tempering,” which may possibly be of con- 
sequence in the study of this most difficult subject. 
In preparing the white alloys containing less than 45 per cent of zinc, I have 
* Loc. cit., S. 396. 
f Observations upon the color of the alloys of copper and zinc which accord very nearly with my own 
are those of Guettier (Dingler's Polytech. J., CXIV. 204, (from the Moniteur Industriel, 1848), and of Lewis 
(Chemical Works of C. Naumann, Abridged and Methodized, with Additions, by W. Lewis, (London, 1759,) 
p. 65), who long ago wrote: “The proportion of Calamine and the increase which the Copper receives 
from it are different in different works: hence the deeper or paler colour of Brass. I have observed in a 
large set of experiments on this subject that a little of the Calamine, that is, of the Zinc contained in Calamine, 
dilutes the colour of the Copper and renders it pale; that when the Copper has imbibed about one twelfth ` 
its own weight, the colour inclines to yellow; that the yellowness increases more and more till the proportion 
comes almost to one half; that on further augmenting the Calamine, the Brass becomes paler and paler, and 
at last white." 
