108 Dr. Matthiessen on an Alloy which may be used 
clude the use of them as standards, and make it desirable that, 
instead of comparing, as heretofore, the conducting powers of 
metals, alloys, &c. with that of silver, copper, or, as has lately 
been proposed, with mercury*, they should in future be com- 
pared with an alloy having the properties mentioned above. 
The alloy best adapted for a standard of resistance for 
galvanic currents, is that composed of 
2 parts by weight of gold +, 
chau i 4) silvers 
for on looking at the curve which expresses the conducting 
powers of the gold-silver alloys{, we find part of it almost at a 
straight line ; that is to say, to the alloy containing 50 volumes 
per cent. of gold (which is the middle point of the straight line) 
one or two per cent. more or less gold may be added without 
altering its conducting power to any great extent. 
In order to test the first condition, I have had the alloys 
made in different parts of the world; and my best thanks are 
due to those gentlemen who kindly undertook the making and 
procuring of them. The following order was given :— 
Take 6 grammes proof, or purest gold, and 3 grammes 
proof, or purest silver; fuse and cast three times§, and then 
draw into wire of about 0°5 millim. diameter. The wire to be 
hard-drawn. 
The alloys experimented with were :— 
No. 1. Made of pure gold and silver by Mr. R. Smith, in Prof, 
Percy’s laboratory. Drawn by Messrs. Watts and Son, of Karby 
Street. These wires were annealed in a red-hot crucible. 
No. 2. Made and drawn in Brussels. Procured for me by my 
friend Mr. G. C. Foster, through the kindness of Prof. Stas. 
Annealed on wire-gauze over a four Bunsen burner. 
No. 8. Made and drawn in New York. Procured through my 
friend Mr. C. M. Warren. Annealed in the same way as No. 2. 
No. 4. Made and drawn in Paris. Procured through Mr. 8, 
Reuter. This wire came to hand already annealed ; therefore no 
determinations of the hard-drawn wire could be made. 
* Siemens, Phil. Mag. (Jan. 1861); Schroder von der Kolk, Poge. Ann. 
vol. ex. p. 452. It should be borne in mind that the use of this metal as 
a standard is open to the following grave objection: viz. that the copper 
wires cr plates dippmg in the mercury will after a time make it im- 
pure ; and as traces of foreign metals (0°1 er 0'2 per cent.) cause a decre- 
ment inthe conducting power of pure mercury (not as stated by Siemens, 
an increment), it would become necessary often to change it, thereby 
requiring a large supply of chemically pure metal. 
+ Corresponding nearly to equal volumes of gold and silver. 
+ Phil. Trans. 1860. 
§ It would have been better to have added, fuse with a little berax and 
dalipelre, 
