34 REPORT— 1901. 



from the pyridine solutions weigh more than those from the aqueous 

 solutions. 



In the measurements of the E.M.F. of the Clark cell by Mr. Glaze- 

 brook and myself the same current was sent through two systems of 

 silver voltameters in series, and 15-5123 grammes were deposited in the 

 bowls which received the greater deposits, as against 15".505.5 grammes in 

 those which gained the smaller deposits. This gives a mean percentage 

 difference of "044, which may be compared with the mean percentage 

 difference of '24 in the present experiments. It is obvious that this 

 difference is of a much higher order, but this difference is a mean of 

 experiments which differ much more between themselves. On that 

 account I think it is better to discuss the experiments in groups. The 

 experiments divide themselves roughly into two groups. There is, first, 

 a group consisting of those in which the current was about "07 ampere and 

 from "5 to 1 ampere. This contains the extremes as regards current, and 

 in it the mean percentage difference would be just over •! per cent. So 

 that for these values of current the deposit from pyridine would weigh 

 almost the same as Schuster and Orossley found for a vacuum, which, it 

 will be remembei'tid, was •! per cent, higher than in air. 



The second group consists of those experiments in which the current 

 value lies between -13 and "41 ampere, and here the mean percentage 

 difference is much larger, i.e., '3S. Over this range one of the deposits 

 seems to be uncertain, and I think these experiments may be considered 

 to indicate that between these values of current in the given bowls one 

 of the two voltameters is irregular in its action. The character of the 

 silver crystals appeared to be variable, whilst the hard film of silver from 

 the pyridine solution had always the same texture. The aqueous volta- 

 meter seemed to work best with the large currents '5 to 1 ampere when 

 the crystals were small, hard, and closely packed. At the lower values of 

 current the silver crystals were thin, long, and friable. At the lowest 

 value they were again small and hard. One explanation of the variation 

 may be that particles of silver are more easily lost during the washing, 

 when the crystals are of the second character. 



Conclusions : — 



(1) That Faraday's law holds to within "24 per cent, in the mean for 

 silver nitrate when dissolved in two different solvents. 



(2) That for current values of "07 and "5 to 1 ampere in the given 

 bowls the amount of silver deposited from a pyridine solution of silver 

 nitrate is neai'ly the same as that deposited from an aqueous solution in a 

 vacuum. 



(3) That for current values between •! and "5 ampfere more silver ia 

 obtained in the pyridine voltameter than in the aqueous voltameter. 



Note on the Variation of tJie Specific Heat of Water, 

 By Professor H. L. Callendar, F.B.S. 



[Ordered by the General Committee to be printed in extenso.1 



The method adopted for determining the variation of the specific heat of 

 water was described and the apparatus exhibited at the Toronto Meeting 

 of the British Association,^ and the results up to a temperature of 60° C. 



' B.A. Eej}., 1897, 



