XI, A, 4 Heise and Clemente: Galvanized Iron 145 



A variation of the solvent ^* makes the subject still more com- 

 plicated. 



In this brief series of experiments there are several "reversals" 

 of potential. Thus copper sulphate attacks both zinc and iron 

 in aqueous solution, as might be expected from its position in the 

 "electrochemical series," but on the addition of ammonia to solu- 

 tions of certain copper salts, the copper apparently occupies a 

 place above iron and below zinc. The same holds true for an 

 alkaline copper sulphate solution (No. 26) . Zinc replaces alumi- 

 nium 2" (Nos. 31 and 32) from aluminium nitrate solution. The 

 last reaction is retarded by the addition of sodium hydroxide. 



Tzentnerschv^er and Druckker*" found that zinc reacts with 

 solutions of cobalt chloride and cobalt sulphate, but only with 

 very concentrated cobalt nitrate solutions. This is interesting 

 in view of our experiments 26 and 27 with cobalt acetate. We 

 have found that an ammoniacal solution of cobalt nitrate (like 

 ammoniacal cobalt acetate No. 27) reacts very quickly with 

 galvanized plate and gives a quantitative separation of zinc from 

 iron. 



The variation in the single potentials of zinc in different 

 aqueous solutions has been studied in detail by Patten and 

 Mott,^^ who found a difference of over 1 volt between the highest 

 (+ 1.0 volt in KOH + KCN) and the lowest (- 0.08 volt in 

 KMnO^ + KjCrO^) values obtained. Other metals doubtless 

 show equally great variations. Perhaps the fact that the po- 

 tential of zinc is lowered in oxidizing solutions such as nitrate, 

 chromate, or permanganate of potassium accounts for the failure 

 of a solution of lead chromate in sodium hydroxide to attack 

 galvanized iron. 



SUMMARY AND CONCLUSIONS 



Various methods of analyzing galvanized iron, or of strip- 

 ping zinc from iron, have been studied and developed. 



The separation of zinc from iron with phosphoric acid, so- 

 dium bisulphate, hydrochloric acid, or sulphuric acid is suffi- 

 ciently rapid and complete to serve as a quantitative analytical 



^ Gates, C. B., Joum. Phys. Chem. (1911), 15, 97; Ghosh, J. C., ibid. 

 (1915), 19, 720. 



" Preliminary experiments in this laboratory indicate that the potential 

 of zinc is several tenths of a volt above that of aluminium in a normal 

 sodium nitrate solution. 



" Tzentnerschwer, M., and Druckker, Y., Joum. Riiss. Phys. Chem. Soc. 

 (1915), 47, 528. 



*" Patten, H. E., and Mott, W. R., Trans. Am. Electrochem. Soc. (1903), 

 3, 317. 



