453 
LORD RAYLEIGH AND MRS. H. SIDGWICK ON THE 
Note to § 26. 
M. Mascart (Journal de Physique, t. iii.; Juillet, 1884) has recently revised the 
calculation of the constant of his apparatus, by which revision the final number is 
altered from '01124 to '011156. 
Note to § 27. 
Although there can be no doubt that silver is greatly preferable to copper for the 
electrolytic measurement of currents, we have thought that it might be useful to make 
a few comparisons of the two metals, so as to allow copper to be referred to on an 
emergency with as much success as the nature of the case admits. The copper 
deposits were taken in the same way as the silver upon platinum bowls, the anodes 
being wrapped in filter paper and suspended at the top of the liquid. On account of 
the tendency to oxidation it is not advisable to allow the copper deposits to soak for 
a long time. They were washed in boiling water for about half an hour, and then 
dried off in the hot closet at 150°. The solutions were made from sulphate, bought as 
pure, no acid being added. Of the four bowls I., II. are large and somewhat deep, 
IIP, IV. are shallow saucers about 3 inches in diameter. In the large bowls the area 
of deposit was about 32 sq. centims., in the smaller about 25 sq. centims. The 
strength of current on the first two occasions was about ^ ampere, on the last about 
§ ampere, thus representing the circumstances for the measurement of the current 
through an incandescent lamp. 
Solution. 
Weight of 
depouts. 
Ratio 
Equivalent of 
Date, 18S4. 
Bowl. 
Mean. 
of copper to 
copper 
silver. 
(silver = lOSh 
Nov. 20 
I. 
Silver nitrate 15 per cent. 
1-38741 
1-3872 
99 
III. 
1-3870/ 
■2937 
3172 
99 * * 
II. 
Copper sulph. sp. gr. l'l 74 
•4065 1 
‘4074 
99 
IV. 
•4082 / 
Nov. 27 
II. 
Silver nitrate 15 per cent. 
1 0523] 
1 0522 
9 9 * * 
IV. 
1 0522/ 
•2934 
3169 . 
99 * * 
99 * * 
III. 
I. 
Copper sulph. sp. gr. 1115 
•3094 1 
•3081 / 
•3087 
Dec. 11 
99 * * 
II. 
IV. 
Silver nitrate 15 per cent. 
3-04891 
3-0487/ 
3-0488 
•2938 
31-74 
99 • * 
” 
III. 
I. 
Copper sulph. sp. gr. 1115 
•8956 / 
•8962 / 
•8959 
Mean 
•2936 
31-72 
Multiplying '2936 by 4 0246 we get 1 *182 grms. as the amount of copper deposited 
per ampere per hour. 
