PKACTlCAL STANDARDS FOR ELECTRICAL MEASURExMENTS. 



33 



same current in silver voltameters containing aqueous and pyridine solu- 

 tions of silver nitrate. 



The platinum bowls used are those numbered I. and V. in the paper 

 on the Measurement of the Electromotive Force of the Clark Cell ' by 

 Mr. Glazebrook and myself. The anode for bowl I. was a silver disc, 

 5 cm. in diameter, hung by a silver rod, and a silver cylinder was used 

 for bowl V. The dimensions of the bowls are given in the paper men- 

 tioned above. 100 c.c. of solution was used in each case, and the pyridine 

 solution contained 10 per cent, of silver nitrate, whilst the aqueous 

 solution contained, as usual, 15 per cent, of the salt. 



The areas of the exposed surfaces were approximately as follows : —■ 



Bowl I. Bowl V. 



Cathode surface . . 75 sq. cm. G7 sq. cm. 

 Anode surface . . 19-6 sq. cm. 18 sq. cm. 



The conditions of current density in the two bowls may be regarded 

 as practically identical. 



The deposit of silver from the aqueous solution was crystalline, and 

 the character of the crystals appeared to vary with the current density. 

 The deposit was washed by standing in distilled water for several hours 

 and dried over an alcohol flame. The deposit from the pyridine solution 

 is continuous, and forms a hard coating : it is washed with water in which 

 both pyridine and -silver nitrate are soluble. It is sometimes slightly 

 coloured, but on drying becomes white. On further heating over the alcohol 

 flame it develops a pearly lustre, and in this condition it has been weighed. 



A Western ampere meter was included in the same circuit, and 

 served to indicate the constancy of the current. The reading of the 

 ampere meter is given in the second column of the table. The variations 

 of the current were very small. In the table the result of every experi- 

 ment which I have made is given. 



(a) and {I)). — In these two experiments the aqueous solution was in a partial 

 vacuum (8 cm. pressure), and -l per cent, has been added to the percentage difference 

 to make them comparable with the other experiments. 



(c). — Fresh solutions were used in this experiment, and the same solutions were 

 used on all subsequent dates. A few particles of silver were lost from the aqueous 

 voltameter in this experiment, August 14. 



The first result of these experiments is clearly that all the deposits 



' rial. Trans., 1892, A. 



D 



1901. 



