﻿LEAD FROM PERCHLOKATE BATHS 



39 



sents a loss of 1.1 pounds per ton of lead refined if the bullion con- 

 tained 5 per cent of impurities. 



Thus the total loss of perchloric acid from unpreventable sources 

 amounts to about 1.5 pounds per ton of lead refined. This does 

 not include any loss from leaky tanks and pipes or careless handling. 



Precautions. Chlorides and barium salts must be absent. A 

 bath that has been giving good deposits will form ver}' bad "trees" 

 if a quantity of Iwdrochlorie acid or some barium per chlorate is 

 added to it. The injurious action of these substances was acci- 

 dentally discovered from the fact that some baths, made from rea- 

 gents containing these impurities, would not give good deposits. 

 There are, perhaps, other salts that would act injuriously, but only 

 those mentioned above have been tried. 



Summary. This paper describes experiments with the lead per- 

 chlorate plating and refining bath. The properties of lead perchlo- 

 rate which are of special value in a plating or refining solution are: 



1. Great solubility. 



2. Cathode deposits which are smooth, dense and free from 

 "trees." 



3. Approximately theoretical corrosion of the anode audi depo- 

 sition upon the cathode. 



4. Absolute stability under all conditions to which it is sub- 

 jected in a plating or refining bath. 



5. Absence of polarization from the formation of lead peroxide 

 on the anode. 



6. Very high electrical conductivity. 



The bath should contain about 5 per cent of lead, 2-5 per cent 

 of free perchloric acid, and 0.05 per cent of peptone. A current 

 density of from 2.3 amperes per sq. dm. (18-27 amp. per sq. ft.) 

 may be used. The peptone is gradually used up, and after about 

 four days a quantity equal to the original amount should be added. 

 The free acid, which is very slowly neutralized by chemical solu- 

 tion of the lead, must be restored hy the treatment of a suitable 

 portion of the solution with the right amount of sulphuric acid. 

 This precipitates lead sulphate and leaves perchloric acid in solu- 

 tion. The filtrate is to be returned to the bath. The bath gives 

 excellent purification, the cathode being about 99.98 per cent pure. 

 The deposit is smootli, coherent, and has a density of 11.36. As 

 a plating bath, the lead perchlorate solution works exceptionally 

 well on account of the absence of "trees" or loose crystals on the 

 edges, even when the deposits reach a thickness of an inch. The 



