144 ; REPORT—1862. 
ferently? This point will be fully discussed in another Report which will be 
laid before your Committee, and in which it will be shown where the hard- 
drawn wires become partially annealed, and annealed wires partially hard- 
drawn, by age. 
It is a curious fact that a change in the molecular arrangement of the 
particles of wire of some metals which may be considered homogeneous has 
very little effect on its clectric conducting power. Thus pure cadmium*, 
which when cold is exceedingly ductile, becomes quite brittle and crystal- 
line at about 80°, and returns again to its ductile condition on cooling, shows 
no marked change in its conducting power at that temperature ; in fact, it 
behaves asif no such change had taken place. Again, when iron wire is heated 
in a current of ammonia it becomes perfectly brittle and crystalline, without 
altering its conducting power to any marked extent. 
That a wire which changes its molecular condition in becoming crystalline 
does not necessarily materially alter in its conducting power, is an important 
as well as a very interesting point, and has also been proved in the case 
of German silver. 
3. On the effect of annealing on the conducting power.—When hard-drawn 
wires of silver, copper, gold, &e., are heated to redness and cooled slowly, 
they become much softer, and on testing their conducting powers they will 
be found to have increased thus :— 
Silver. Copper. Gold. According to 
Taking the hard-drawn 
WATE) 2). Sidr Her! 100-0 100-0 100-0 
The annealed will be.. 107-0 102-6 101-6 Beequerely. 
iid cee itr aot 1090 1023 1020 | a 
von Boset. 
Ditto wed saaidatsliia. « 110-0 106-0 —  fS&emens$§. 
Now there is a certain difficulty in drawing a wire which is hard-drawn ; 
and if annealed wires be used for the reproduction of standards, the molecular 
condition, or perhaps the process of annealing, has an influence on the incre- 
ment of the conducting power. Thus, according to Siemens|', the difference 
in the conducting power between hard-drawn and annealed silver varies be- 
tween 12:6 and 8 per cent., and that of copper between 6 and —0°5 per cent. ; 
according to Matthiessen and von Bose@, that of silver varies between 10 
and 6 per cent., and that of copper between 2-6 and 2 per cent. 
Again, the annealed wires of pure metals are so soft that they would easily 
get damaged in covering them with silk or winding them on the bobbins, so 
that in using them the utmost care would have to be employed in order to 
prevent their getting injured. 
4. On the influence of temperature on the electric conducting power.—It has 
been shown that the conducting power of most pure metals decreases, 
between 0° and 100°, 29-3 per cent.: pure iron has been found to form an 
exception to this law, its conducting power decreasing between those tempera- 
tures 38:2 per cent. If pure metals be therefore used as standards, very 
accurate thermometers are necessary, as an error of 0-1° in comparing 
two standards would cause an error in the resistance of about 0-04 per cent. 
Now there is great difficulty in obtaining normal thermometers; and we must 
* Phil. Trans. 1862, pt. 1. 
t Ann. de Chim. et de Phys. 1846, t. xvii. p. 242, {+ Phil. Trans. 1862, pt. 1. 
§ Phil. Mag. Jan. 1861. || Phil. Mag. Jan, 1861. 
*| Matthiessen and Vogt’s unpublished researches. 
