' ON STANDARDS FOR USE IN ELECTRICAL MEASUREMENTS. 127 
' Wire VII. was a wire sent me by Mr. H. A. Taylor, and had to be 
_ drawn down before it could be measured ; another piece of the same wire 
drawn down on a different occasion gave the same value; this wire has 
the lowest resistance of any I have obtained; it has, too, the highest 
_ specific gravity. Mr. Taylor says of it ‘that it has a higher tempera- 
ture coefficient than that given by Matthiessen.’ 
VIIL. was a sample of wire obtained from Germany, and said to be 
electrolytically prepared; its high resistance is, I think, due to the 
presence of oxide, as I fused some of it in hydrogen, and when measured 
_ partially annealed it gave the value 1566 at 18° for the wire, 1 metre 
_ weighing 1 gramme. 
F IX., X., and XI. are wires of my own preparation. Pure copper was 
5 prepared electrolytically by Messrs. Sutton, of Norwich, and supplied 
me in thin sheet, and this was fused in a porcelain tube 18 centimetres 
in length and 1 centimetre in diameter; the tube was fitted up in a 
small furnace made of sheet iron, and lined with ganister; this was 
heated rapidly in a blast flame led in at the bottom. Some difficulty was 
_ experienced in obtaining the copper in a solid cylinder. In the early 
experiments hydrogen was passed into the tube while the copper was 
being fused, and was made to bubble through the molten copper; on 
breaking the tube the copper was found to be full of small holes; the 
copper had absorbed the hydrogen at the high temperature and given it 
off again on cooling; on another occasion the copper was fused down in 
hydrogen, and the tube was connected with a water-pump and exhausted 
and the copper allowed to cool in a vacuum; this gave a more continuous 
cylinder. It was found best to fuse the copper under borax, after pre- 
vious reduction ; a good cylinder of the metal was thus obtained. 
I was unfortunately not able to draw down the copper for myself; 
this was very kindly done for me by Messrs. Smith, of Halifax, and 
Messrs. Johnson & Matthey. The porcelain tubes had been prepared 
of such a size that the cylinder of copper could be drawn without 
further heating; the copper, therefore, was not fused after it left my 
hands. 
Two sheets of the electrolytically prepared copper were fused on 
different days, and one cylinder was sent to Messrs. Smith to be drawn, 
and the other to Messrs. Johnson & Matthey. 
Wires IX. were drawn by Messrs. Smith, wires X. by Messrs, Johnson 
& Matthey. 
Wire XI. was drawn by Messrs. Johnson & Matthey from a sample of 
copper which I prepared by electrolysis from a pure solution of copper 
‘sulphate ; the copper was deposited on a plate of copper, which had had 
its surface rubbed over with graphite; by this means the deposited copper 
was easily stripped off the plate; the other plate was of platinum. After 
@ time the solution was changed ; the deposition was very slow, as it was 
thought that there would be less likelihood of copper sulphate getting in 
between the layers of copper. The deposit was boiled with dilute sul- 
phuric acid and then in water, and was afterwards fused as above 
described. 
Wires IX. were measured as received; this accounts for the close 
agreement between the two determinations, Wires X. and XI. I had to 
draw down further to measure them on my bridge. 
Wires X. (2) and XI. were drawn down with great care and not so 
much as X. (1). 
