XI, A, 4 Witt: Testing of Galvanized Iron 153 



be noticed on the last one, even after several hours. The essen- 

 tial difference between this and the previous experiment was 

 that in this case the solution was always acting on zinc rather 

 than on any of the zinc-iron alloys. It might be expected that 

 more of the lead could be removed. This was found to be true, 

 for the analysis showed 2.62 grams lead acetate per liter. 



A lead acetate solution which contains no zinc ions can be 

 still more dilute and attack a galvanized surface. Some of the 

 original solution was diluted to various concentrations with 

 distilled water, and each was tried with a fresh piece of gal- 

 vanized iron. A solution containing only 0.5 gram lead acetate 

 per liter showed some action. This may be made clearer by 

 summing up the results. 



Table I. — Minimum strength of active lead acetate solution under various 



conditions. 



Lead acetate 

 per liter. 

 Condition. Grams. 



Solution containing no zinc ions and acting on outer 

 zinc coating 0.50 



Solution containing zinc ions and acting on outer zinc 

 coating 2.62 



Solution containing zinc ions and acting on the zinc-iron 

 alloys 57.05 



These results indicate that each of the three factors men- 

 tioned above has its effect on rendering the acetate solution 

 inactive. It is likely that the relative importance of each varies 

 with the temperature, concentration of the solution, and char- 

 acter of the zinc-iron alloys. However, the net result is that 

 more than the theoretical amount of lead acetate is required, and 

 consequently the cost of each test is increased. 



THE HYDROCHLORIC ACID METHOD 



Hydrochloric acid ^^ may be used for removing the coating 

 from galvanized iron if the temperature and concentration 

 are kept within certain limits. A solution made from one part 



" After the present paper had been completed, I received an abstract of a 

 paper by Aupperle [Metal Ind. (1915), 13, 329; Iron Age (1915), 96, 132]. 

 Aupperle uses hydrochloric acid having a density of 1.20, containing a small 

 amount of antimonous chloride. The samples are cut 5.72 by 5.72 centi- 

 meters (2.25 by 2.25 inches). He objects to the Preece test, because of 

 its unreliability, and to the lead acetate method, because of the long time 

 required. 



The results obtained in this laboratory show that if a lower density of 

 acid is used no addition of any salt is necessary. The disadvantages of 

 such small pieces have already been discussed. 



