﻿LEAD FROM PER CHLORATE BATHS 



33 



were used in a few experiments. Tlie solutions were stirred by a 

 current of air during the day and l3y a current of hydrogen gas at 

 niglit. Tlie hydrogen generator ^va> I'lmnected that it automat- 

 ically kept up the current of gas at thi times when the laboratory 

 air blast w^as not runniug. A very slow current of gas through the 

 solutious seemed to be the best laboratory substitute for the circu- 

 lation of the electrolyte from tank to tank Avhich is practiced in com- 

 mercial w'jrk. The sreatest objection to the use of the current of 

 gas is that it stirs up slime from the bottom of the vessel. Some 

 of these imptirities adhere to the cathode. This greatly lowers the 

 puritA' of the deposited lead. 



Addition Substances. The lead perchlorate bath does not give 

 good deposits without the use of some ' ' addition substance. ' ' except 

 at very low current densities. Numerous experiments w^re tried, 

 using high concentration of perchloric acid and of lead, but no satis- 

 factory results were obtained. 



The addition of small amounts of certain substances to plating 

 and refining baths for the purpose of eliminating or restraining 

 crystals and of improving the density, color and smoothness of the 

 deposits, has been a ver^' common practice, or. at least, has been 

 f r e C|U en t ly des c rib e d . ^ - 



Perhaps the best Imown example in commercial work is the use 

 of glue in the lead fluo-silicate bath described by Belts. His patent 

 calls'" for '"reducing agents."" and he tiuds that "gelatine, -pyro- 

 gaUol, resorcinol. saligenin. orthoamidophenol. hydroquinone and 

 sulphurous acid"" are available. He recommends gelatine because 

 it is the cheapest and gives the best results. 



In the course of this work many different addition substances 

 were tried. Tannin, pyrogallol. resorcine. licorice and eucalyptus 

 extract all helped to a considerable extent, but ''trees"' would form 

 at the corners of the cathode whencA'er the deposit reached a cer- 

 tain thickness. Tannin might be successfully used if no better sub- 

 stance were available. A high-grade gelatine, which was purchased 

 for use in bacteriology, gave poor results. A commercial grade of 

 glue gave fair deposits. Ordinary commercial glue, which is used 

 in the lead fluo-silicate baths instead of the more expensive gelatine, 

 is a very impure product, containing many things, among them 



Kern. Tnipaacllops American Electrochemical Society, XV, 441 (1909). 

 Warts. Electro ihci an urgy, pp. lo. 46. 76 (189.5). 

 McMillen, A Treatise on ElectrometaUurgy, p. 9 (1890). 

 i^Betrs. r. S. Parenr. 71 S. 277 (1902). 



