ON THE ALLOYS OF COPPER AND ZINC. 45 
The contents of the capsule are now treated with dilute chlorhydric acid, in which 
the subsalt is readily soluble, washed with water, and added to the original copper, 
the washing of which is to be continued till the last traces of acid are removed. 
The copper, having been transferred to a porcelain boat,.was dried at 100? C., 
ignited in a current of hydrogen gas, and subsequently weighed. 
The iron used in these assays was that known as the “best Russia sheet" In 
order to obtain the best possible pieces, I have followed the custom of copper assayers 
in allowing a sheet-iron worker to cut up a number of pounds of Russia sheet into 
bits of about two and a half by three and a half inches, this size having been found 
well adapted to the work at hand, smaller pieces being unequally corroded; from 
this supply only those pieces which presented a perfectly smooth and even sur- 
face were selected for use. Those pieces which are at all corrugated or uneven 
ought to be rejected, for such are acted on unequally by the acid, and copper 
would be lost in the cavities thus formed. 
Since the sharp angles of these rectangular bits of iron are liable to be corroded 
very much by the acid, in which case particles of iron might drop off and con- 
taminate the copper, it is best to remove them by means of a rasp, and to make 
the corners round and smooth. 
The glazed coating which occurs upon the surface of Russian sheet-iron, and 
which, according to Wells,* consists of silicate of iron, is readily removed by di- 
gestion in moderately dilute chlorhydric acid, in which it soon falls off in flakes. 
After washing with water, the bits of iron are dried and preserved for use. 
In conducting the assay it is of importance that the solution should be dilute, 
since the precipitation of the copper in this case goes on more regularly, and is 
sooner completed; it should be warm, not only that the copper may be precipitated 
more rapidly, but in order to avoid the formation of a basic iron salt, which is 
very liable to contaminate the copper when it is precipitated in the cold. This 
basic salt frequently forms during the precipitation, even in warm solutions, if they 
are not sufficiently acidulated. If a solution be at the same time somewhat con- 
centrated, and not sufficiently acid, it often happens that a portion of the copper 
becomes so firmly attached to the iron that it cannot be rubbed off. This accident 
will rarely occur, however, to any one accustomed to the assay. 
It is remarkable that no one who has written upon this process has, so far as 
I can ascertain, appreciated the necessity of igniting the dry copper in a current 
* Proceedings of Boston Society of Natural History, IV. 296. 
