Thin Metal Partition in a Voltameter. 289 



plates 4 centim. wide, 6 centim. long, and 1 millim. thick 

 were bored with a hole 1*5 centim. in diameter. Powdered 

 sealing-wax was placed around the edge of this hole, melted, 

 and the gold-leaf secured to the melted sealing-wax. 



This plate was then securely and perfectly (i. e. with no 

 possible chance for leakage) sealed upon the side of the inner 

 jar so that the gold-leaf was over the hole almost centrally. 

 The voltameter was then carefully filled, keeping the liquid 

 inside and outside on the same level so as not to break the 

 gold-leaf partition, and was then ready for use. 



To measure the current, a Thomson No. VI. Composite 

 Electric Balance (No. 106), and a Weston double-scale 

 ammeter No. 598, ranging from to 1*5, reading directly to 

 •01 ampere and estimated to - 001, and from to 150, read- 

 ing to amperes and estimated to *01, were used in series 

 with the voltameter. The two instruments were found to 

 agree so well that the Weston ammeter was used alone for 

 most of this work as it was much more convenient to read. 



The battery consisted of 25 Accumulator Company 

 " 23 M " type accumulators, 350 ampere-hours capacity, 

 50 volts E.M.F. The current-strength was adjusted to any 

 desired value by resistance in series, which could be varied 

 at pleasure between zero and 12,000 ohms. For sealing-wax, 

 pure rosin and bees- wax (without colouring-matter), mixed 

 in such proportion as to give a low melting-point, was used. 

 The gold-leaf used was bought in Nashville, and is known to 

 the trade as " XX." It is about '0001 millim thick. 



Careful selection was made of such parts of the gold-leaf as 

 were found, by holding up to the light, to be free from small 

 holes. It has already been observed, in Part I. of this paper, 

 that when CuS0 4 was used as the electrolyte and the current- 

 strength was over *3 ampere, Cu was deposited on the rim of 

 the gold-leaf, which was necessarily larger than the hole in 

 the glass plate. In this work it was found necessary to 

 remove this gold quite close up to the edge of the hole by 

 scraping it off", as was first tried, or by covering it carefully 

 with sealing-wax, which was found both easier and better. 

 This was accomplished by melting the sealing-wax over the 

 gold with a hot brass hammer of peculiar shape made for the 

 purpose. The wax could thus be made to flow quite close 

 to the edge of the hole. This left only that part of the gold 

 exposed which was immediately over the hole. To neglect 

 this was in all cases to reduce the critical current, the deposit 

 of the cation appearing first on that part of the gold-leaf 

 which was nearest the anode and farthest from the opening. 



