﻿36 



INDIANA UNIVERSITY 



centrated solutions, high per cent of free acid, large amounts of 

 peptone, and good stirring. With 5 per cent lead, 5 per cent 

 perchloric acid, 0.05 per cent peptone and enough stirring or mix- 

 ing of the solution to prevent large differences in concentration 

 between the top and the bottom, a current density of from 2 to 3 

 amperes per sq. dm. (18 to 27 amperes per sq. ft.) gives good 

 deposits, as shown by the accompanying photographs. With lower 

 current densities, less care need be taken with stirring, proper spac- 

 ing of the electrodes, aciditj^ and quantity of peptone. For plating 

 purposes, low current densities are recommended. With 0.4 am- 

 peres per sq. dec, fair deposits may be obtained from baths con- 

 taining only 0.2 per cent free perchloric acid. With higher cur- 



II.— Photogkaph Showing the Effect of Current Density. 

 1 amp. per sq. dec, 5.5 per cent lead; 2 amp. per sq. dec, 4.5 per cent perchloric acid; 

 4 amp. per sq. dec, 0.05 per . cent peptone. 



rent densities, these neutral baths give poor deposits, even when 

 large amounts of peptone are used. 



Voltage. The relation between concentration of the solution, 

 current density, and fall in potential or volts is shown in the follow- 

 ing table. These measurements were made upon baths which had 

 been running for several days and which were giving excellent 

 deposits. The anodes were of ordinary commercial lead from a 

 plumber's scrap pile. Two anodes were used — one on each side of 

 the cathode. The anodes had been made purposely smaller than the 

 cathodes to prevent, as much as possible, the thickening of the cath- 

 odes at the edges. 



