1894.] Specific Resistance of Pure Electrolytic Copper. 71 



tank from ordinary sulphate of copper solution prepared from pure 

 crystallised sulphate of copper, pure sulphuric acid, and distilled 

 water. The anode was a large plate of ordinary commercial electro- 

 lytic copper, and the cathode was a large polished plate of rolled 

 copper. Before placing the cathode in the bath it was silvered by 

 rubbing it over with a solution of cyanide of silver in potassium 

 cyanide. This coating of silver was converted into iodide of silver 

 by means of a solution of iodine in potassium iodide. As is well 

 known, this treatment renders the stripping of the deposit from the 

 cathode an easy matter. On this cathode copper was deposited to a 

 thickness of 2'5 mm., and then the deposit was stripped off. Several 

 deposits were made and tested roughly, as stated in the beginning of 

 this paper. The best of them was one marked " A." 



Preparation of the Wire. A strip was cut from the deposited sheet 

 of copper, filed round, and then drawn through sapphire dies to a 

 diameter of approximately 0'02 in. 



These determinations were made by means of the hydrostatic 

 balance principle. A re-determination of the specific gravity of the 

 copper I in the above table was made by means of a picnometer. 



Picnometer + distilled H 2 at 15 C. = 91-2878 grams. 



+ specimen + = 123'3562 



Specimen = 36'1012 



. ' . weight of displaced H 2 = 4'0328 ,. 



Specific gravity 8'9519. 



As is seen from the above numbers, the specific gravity of copper 

 when it is pure varies very little with hardness and other conditions, 

 the variations when at a maximum only amounting to 0'0004 of the 

 Avhole. The mean of the above results may, therefore, be taken as 

 the specific gravity of this copper at 15 C. The mean is 



8'9oll = the specific gravity. 



This value is not the one required for the calculation of the dimen- 

 sion of wires ; what is required is the density or absolute weight of 

 an ideal cubic centimetre of the metal at 15 C. The weight of 

 1 c.c. of water at 15 C. is, according to Kohlrausch, ' Praktische 

 Physik,' 



0-99915 gram. 



The specific gravity of the copper divided by this figure gives the 

 density : 



Weight of 1 c.c. of copper at 15 C. 8'9587 grams (8'959). 



Specific Resistance of Deposit "JL " (hard drawn) at different Tem- 

 peratures "between 12'9 C. and 90'2 C. A hard-drawn wire of the A 

 deposit was measured by the apparatus described. For determining 



