126 REPORT—1890. 
ductivities, with the view of comparing them with Matthiessen’s 
standard. Application was therefore made to several firms for high- 
conductivity copper wires. My thanks are due to those who sent 
samples. 
A table of results for all the specimens tested is given, and it shows 
the variation in resistance of high-conductivity wires. 
TV. and IV!’ are the same copper, but IV. is hard drawn, IV.’ is 
annealed ; they were measured just as they were sent from the manu- 
facturers; the same is true of V. and V.’, VI. and VL.’ 
Tt will be noticed that VI. and VI.’, which are of considerably less 
resistance than the other wires, are of higher specific gravity: the firm 
that sent them thus wrote of them: ‘It is only occasionally we come 
across copper as high as this or high enough to be called the highest (in 
conductivity) we can produce. ‘This copper has been produced electro- 
lytically by our ordinary process.’ How this copper was treated after 
electro-deposition I do not know. T am inclined to think from my own 
experience that this difference in density is due rather to the condition of 
the copper than to its relative purity. Matthiessen found that very 
small quantities of impurities reduced the conductivity 20 or 30 per cent., 
and a sufficient amount of impurities to cause this decrease in density 
from 8°94 to 8°90 must make a larger increase in the resistance of the 
copper. 
Phe temperature coefficient is stated to be different for various 
specimens of metal, according to their purity. Matthiessen himself seems 
to have been of this opinion; but the mere difference in density of the 
metal might be expected to affect the alteration of conductivity with the 
same change in temperature. I have not been able to find any experi- 
ments bearing on this question. It is quite easy to obtain samples of 
wire of different density by varying the process of drawing, and the 
temperature coefficients of such wires might be found to be different. 
Comparing V. and V.’ with VI. and VI.’ it is seen that with this in- 
crease of density there is a distinct diminution in the effect of annealing. 
Iv. — IV.’ oosir | 
V.— V2! = ‘00577 
VI. — VI.’ = -004 
T thought it might be possible that VI.’ was not completely annealed, 
so, for a direct comparison, two specimens of VI., which had been 
measured hard drawn on July 10 and 14, 1890, were annealed; for this 
purpose a flat copper vessel was made of about 2 cm. height and 18 in 
diameter, with a closely fitting lid; the wire was packed in this between 
sheet asbestos, which had been previously heated ; the vessel was filled up 
with lampblack, and heated over a big bunsen burner and gradually 
cooled; the process generally took about twenty-four hours ; the wire 
was found not to be oxidised after the process was over. 
Wire Hard-drawn Annealed Difference 
I. 1549 1510 00389 
II. 1548 1509 ‘0039 
The difference Matthiessen obtained was ‘0038. 
The above method of annealing was found very effective. Silver 
wires, which on annealing decrease 10 per cent. in resistance, gave the 
same value after a second annealing as they did on the first occasion. 
A 
