Let x be percentage of copper, then 100 — x is percentage of "ferromanganese."
| Values of x. | 100 | 99.26 | 91 .88 | 86.98 | 80.4 | 70.65 |
| Specific resistance with respect to copper (? pure) | 1 | 1.19 | 11.28 | 20.4 | 27.5 | 45.1 |
| Temperature coefficient per degree x 106 (hard) | 3202 | 2167 | 138 | 16 | 22 | -24 |
| Ditto (soft) | 184 | 80 | 66 | 21 |
If nickel is added, alloys of much the same character are obtained, some with negative temperature coefficients — for instance, one containing 52.51 per cent copper, 31.27 per cent ferromanganese, and 16.22 nickel.
A detailed account of several alloys will be found in a paper by Griffiths (Phil. Trans. 1894, p. 390), but as the constants were determined to a higher order of accuracy than the composition of the material — or, at all events, to a higher degree of accuracy than that to which the materials can be reproduced — there is no advantage in quoting them here.
[ELECTROPLATING AND ALLIED ARTS]
This is an art which is usually deemed worthy of a treatise to itself, but for ordinary laboratory purposes it is a very simple matter — so simple, indeed, that the multiplicity of receipts as given in treatises are rather a source of embarrassment than otherwise.
The fundamental principles of the art are:-
(1) Dirty work cannot be electroplated.