ROSA AND VIXAL: THE SILVER VOLTAMETER 453 



1.1175 mg. per coulomb as the mean. They originated the porous 

 cup voltameter, which was very satisfactory and has been much 

 used since. 



Kahle, in 1899, published the results of his extended researches 

 on the voltameter. He noted a characteristic striated appear- 

 ance of the deposit when the solution was used several times. 

 The liberation of acid he concluded accompanied the formation 

 of oxidation products at the anode. His value for the equivalent, 

 using Clark cells as reference standards, was the same as found 

 by the Kohlrausches. Leduc (1902) believed that the anode 

 current density ought to be very small, so that the quantity of 

 acid produced should be a minimum. He thought also that 

 the presence of AgOH, if in solution, is not detrimental, and 

 recommended neutralizing the electrolyte with Ag 2 0. Mylius, 

 in 1902, called attention to the possibility of producing a red 

 silver precipitate by the action of filter paper on AgN0 3 . The 

 significance of this observation was apparently not appreciated 

 until recently. 



The first work at the Bureau of Standards on the voltameter 

 was by Dr. Guthe in 1904, who compared several different forms 

 and particularly noted the difference between the porous cup 

 and filter paper voltameters. 



Van Dijk in 1906, compared the porous cup and filter paper 

 forms of voltameter, and found the difference to be 0.023 per 

 cent, which he ascribed to the complex ion yielding an excess 

 deposit in the former. He gives as the electrochemical equivalent 

 of silver. 1.1180 mg. per coulomb. Duschak and Hulett obtained 

 a high degree of reproducibility, and made a careful analysis of 

 their deposits, finding inclusions amounting to about 0.011 per 

 cent. 



The important recent investigations of the national laborato- 

 ries of England, France, and Germany have been published by 

 Smith, Mather, and Lowry; Janet, Laporte, and de la Gorce; 

 Jaeger and von Steinwehr, respectively. Absolute balances were 

 used to measure the current in the first two, and in the last the 

 voltage of the cadmium cell was determined on the assumption 

 that the electrochemical equivalent of silver is 1.118 mg. per 



