GALVANIC ZINCKING. 83 



brass plate being the positive or decomposing pole. For large 

 articles, the number, and not the size of the pairs must be 

 increased. A coating of varnish is necessary to protect the 

 plated surfaces from oxidation by exposure. 



Salzedes's method (Ch. Gaz. vi. 227) is similar to the forego- 

 ing, but is more expensive, as it requires, in addition, the use 

 of cyanide of potassium. 



Lead : its Reduction in the wet way. — Sulphate of lead 

 is a large secondary product in dyeing and other technical 

 processes, and may be reduced, according to Trommsdorff, in 

 the following manner. (Kunst u. Gewerbebl. d. k. Baiern, 

 May, 1846, p. 330.) 10 pts. sulphate of lead and 1 pt. com- 

 mon salt are mixed with water to a paste, and bars of zinc 

 immersed into the liquid. Grayish-black metallic lead is 

 separated in a short time, and the solution contains sulphate 

 and chloride of zinc. The lead is very pure. Bolley observes 

 that the lead is left in a spongy state, and may be compressed 

 into any required form. 



Tinning and Leading Vessels of CopjMr or Iron. — Accord- 

 ing to Golfier Bessiere, vessels of copper and iron may be 

 easily and strongly coated with lead or tin, by employing 

 soldering salt (chloride of tin and ammonium) instead of 

 salammoniac, during the operation. It thoroughly cleanses 

 the surface from rust. 



Iron Leaded. — Parkes (Chem. Gaz. 1848) has given a new 

 method for coating iron and steel with lead. The metal is to 

 be scoured and dipped into a bath of 9 pts. of lead with 3 pts. 

 antimony, or into one of 9 pts. lead, 1 pt. tin, and 1 pt. an- 

 timony, the surface of either of which must be covered with 

 fused chloride of barium and chloride of sodium, or a mixture 

 of both. 



Galvanic ZincJcing — Kiepe made some experiments on this 

 subject, under Dr. Eisner's direction, which resulted as follows. 

 Wrought and cast-iron was readily coated with .zinc, with the 

 aid of a galvanic battery, by employing a solution of freshly- 

 precipitated zinc in saturated sulphurous acid water, or a 

 solution of the double salt of chloride of zinc and ammonium, 



