ON STANDARDS FOR USE IN ELECTRICAL MEASDKEMENTS. 141 



Table III. — German-silver. 



The above table shows clearly that annealing a wire after v^inding 

 has a very good effect on the constancy of the resistance. 



Quite analogous results were obtained with other alloys containing 

 zinc, e.g., nickelin, which has been much used for standards in Germany. 

 The less the percentage of zinc, the less became the above-mentioned 

 variations of resistance. 



As these zinc-containing alloys showed themselves so unreliable, we 

 extended our investigations to other alloys. 



A few years ago the firm of Siemens & Halske in Berlin made use of 

 an alloy on account of its comparatively low tempei-ature-coeflficient (0-02 

 per cent, per 1° C), called patent-nickel. This was tested in the 

 Keichsanstalt in the same way as the other alloys. It contains about 

 25 per cent, of nickel and 75 per cent, of copper. The experiments 

 gave the following results : — 



1. The variations of resistance by winding are considerably less for 

 this material than with alloys containing an appreciable amount of zinc. 



2. Heating produces a decrease of resistance ; this decrease is some- 

 times greater than the increase by winding, because the hardening 

 produced by drawing the wire is also diminished. There is, however, 

 not the slightest evidence for a change of molecular structure. 



Materials with such properties are evidently much more appropriate 

 for the construction of standard resistances. It was, indeed, found, by 

 comparison with mercury resistances, that coils of ' patent-nickel,' which 

 had been, as we call it, artificially aged by heating at about 140° C, have 

 I'emained constant for two years within a few thousandths per cent. In 

 the following table, for instance, ai'e stated the differences of two patent- 

 nickel standards of 1 ohm (No. 22 and No. 23), as observed at different 

 times : — 



