454 ROSA and vixal: the silver voltameter 



coulomb. The English and French work was based on the filter 

 paper voltameter. 



The work of the present authors, carried out in 1908-09, is 

 described in the first of a series of four papers. In the other 

 three, in which Dr. A. S. McDaniel is a joint author, the con- 

 tinuation of the work during the years 1909-12 will be described. 

 The second paper of the series will deal with the chemistry of 

 the voltameter, and the theory of striated deposits, the third 

 will treat largely of the purification and testing of materials, and 

 give the second series of quantitative results, while the fourth 

 and last paper will give the results subsequent to the International 

 Technical Committee's work. 



In this investigation, ten platinum and two gold dishes have 

 been used: four large dishes (350 ce.),«four medium (175 cc), and 

 four small ones (125 cc). All the dishes of one size were adjusted 

 to the same weight to facilitate the weighings, which were made 

 on three balances (one for each size of dish) mounted on piers 

 in a special constant temperature room, so arranged that the 

 balances could be read by telescope and scale from outside the 

 room. For weighing the dishes, similar ones reserved for tare 

 were used, and the silver was counterbalanced by special silver 

 weights, gold plated. Buoyancy corrections were thus eliminated. 

 The types of voltameters used were (1) the Rayleigh or filter 

 paper form, (2) the Richards or porous cup form, (3) the Poggen- 

 dorff form without septum, excepting a glass cup, hung under 

 the anode, or with silk around the anode, (4) the siphon type. 



The deposits were timed automatically by a chronograph, and 

 the ticks of a standard Riefler clock. The circuit was so arranged 

 that the current could, after adjustment, be thrown on to the 

 voltameter circuit and maintained constant to usually better 

 than 1 in 100.000 during the course of the experiment. Partic- 

 ular attention was paid to the insulation resistance. The refer- 

 ence standards were a Wolff manganin coil of 1 or 2 ohms in oil, 

 and four standard cells in an oil bath maintained at a fixed tem- 

 perature. The drop in potential across the standard resistance 

 was made equal to the voltage of one of the cells and kept so by 



