190 
DBS. A. MATTHIESSEN AND C. VOGT ON THE INFLUENCE OF 
The values in Table XIX. indicate that the law will probably hold good for most of 
the three metal alloys. 
There is, however, one of the three metal alloys which we cannot pass over unnoticed, 
namely, that of copper-nickel-zinc or argentan (german silver). This alloy has long 
been used, on account of the small effect which temperature has on its conducting-power, 
for making resistance coils, &c. It is a somewhat curious fact, that the conducting- 
power of this commercial alloy decreases less between 0° and 100° than almost any other 
alloy yet known, for in the course of this investigation we have only found the following 
which show a smaller percentage decrement in their conducting-power than argentan. 
The conducting-power of the platinum-silver alloy, containing 19-65 volumes per cent, 
platinum, decreases between 0° and 100° 3T0 per cent. 
The conducting-power of the palladium-silver alloy, containing 23-38 volumes per cent, 
palladium, decreases between 0° and 100° 3 "40 per cent. 
The conducting-power of the iron-gold alloy, containing 10-96 volumes per cent, iron, 
decreases between 0° and 100° 3-84 per cent. 
The conducting-power of the argentan decreases between 0° and 100° 4-39 per cent. 
III. On a Method by which the Conducting-power of a Pure Metal may be deduced from 
that of the Impure one. 
This part of our subject is an important deduction from the law 
Po . Pc : : > M00 o : x 100 ° ; (1) 
for if we consider the two last terms of the proportion, and bear in mind that a small 
amount of another metal has very little or no effect on x' 100O , when it represents the con- 
ducting-power of an alloy containing a very small percentage of the one metal, whereas 
it has a very considerable one on X 100 o, we may write the proportion 
P : P' : : M 100 ° : M' 100 ., (5) 
where P and P' represent the observed and calculated percentage decrements in the con- 
ducting-power of the impure and pure metals between 0° and 100°, and M 100 ° and M' 100 c 
their conducting-powers at 100°. P' is for most metals 29-307, or we may express it 
as follows : — 
The percentage decrement in the conducting-power of an impure metal between 0° C. 
and 100° C., is to that of the pure one between 0° C. and 100° C. as the conducting-power 
of the impure metal at 100° C. is to that of the pure one at 100° C. 
From the results given in Tables XII. and XIII., we have chosen the following alloys 
to show that a small amount of foreign metal has no influence on the value X' 100 o, which 
may therefore be looked upon as equal to M' 100 .. 
