152 



The Philippine Journal of Science 



1916 



that considerably more than this amount is necessary, because 

 the solution becomes exhausted long before all the lead has been 

 removed. Three causes for this may be suggested. 



1. The concentration of the lead ions is diminishing. 



2. The concentration of the zinc ions is increasing. 



3. The removal of the alloy layers is much slower than that of 

 the zinc itself. As a result the reaction almost ceases unless 

 there is a large excess of lead acetate present. 



In order to determine the effect of each of these factors, the 





Rejected portion. 







18.34 



18.95 



18.17 



18.94 



20.08 





18.18 



18.34 







18.85 



18.50 





19.57 



18.93 



19.79 



17.89 



18.40 



18.20 



18.38 



19.00 



Fio. 1. A galvanized sheet was taken at random. A piece was cut 60 by 75 centimeters, 

 rejecting the portion at the end and sides. This was then cut into squares 15 by 16 centi- 

 meters, and each was numbered so that its original position on the sheet might be known. 

 The numbers in the diagram show the weight of coating in grams found on each square. 

 The squares were cut accurately, so that the variation in results is almost entirely due to 

 variation in the coating itself. 



following experiments were carried out. One of the 15-centi- 

 meter squares was placed in a quantity of lead acetate solution 

 containing the theoretical amount of lead necessary to replace 

 the zinc, and although it was left for a number of hours, with 

 frequent removals for cleaning off the precipitated lead, not 

 all the zinc was removed. The action did not altogether cease, 

 but was so slow that it was worthless. On analysis this nearly 

 exhausted solution was found to contain 57.05 grams lead acetate 

 per liter. 



Another portion of lead acetate solution was subjected to 

 immersions of fresh galvanized sheets until no more action could 



