ZI.A,4 



Heise and Clemente: Galvanized Iron 



141 



strip zinc, whereas lead chromate dissolved in sodium hydrox- 

 ide leaves galvanized iron unattacked. 



Copper salts, which generally attack both zinc and iron, may 

 have selective action in alkaline solution (Nos. 25 and 26). 

 Ammoniacal and alkaline solutions of salts of other metals, such 

 as aluminium (Nos. 31 and 32), cadmium (Nos. 23 and 24), 

 cobalt (Nos. 27 and 28), and chromium (Nos. 29 and 30), have 

 selective action, although the salts themselves have little or no 

 such effect. 



Of the cases mentioned, the precipitation of such metals as 

 chromium, copper, lead, and aluminium from alkaline solution 

 is of special interest because of the uncertain position of the 

 metals in the complexes formed when their salts are dissolved 

 in alkalies. 



The fact that iron is generally attacked very little when it 

 is used as anode in alkaline or oxidizing solutions has long been 

 made the basis of methods of separation of metallic coatings 

 from iron.^^ The separation is sufficiently complete and clean 

 cut to serve as a rapid and accurate method of analysis of 

 galvanized iron, as the results in Table III show. In the experi- 

 ments here recorded, no particular effort was made to regulate 

 the current. A voltage of about 3 and a current density of 

 approximately 15 to 25 amperes per square decimeter were 

 maintained, the stripping being completed in a few minutes. 

 The galvanized iron was cut from the sheet used in the tests 

 enumerated in Table II. 



Table. III. — Stripping of zinc from iron with the aid of an electric current. 



Exper- 

 iment 

 No. 



Bath. 



Sample. 



Weight. 



IPotassiom chlorate, saturated solution--. 



IPotasBsum nitrate, saturated solution 



Sodium nitrate, 30 per cent solution 



[chromium nitrate, 20 per cent solution... 



Potassium hydroxide, 20 per cent solution 

 Sodium hydroxide, 20 per cent solution .. 



Grams. 

 1.996 

 2.766 

 2.300 

 2.229 

 4.055 

 2.601 

 2.455 

 3.918 

 4.454 



Loss. 



Grams. 



0.189 

 0.264 

 0.217 

 0.213 

 0.393 

 0.274 

 0.263 

 0.380 

 0.422 



Per cent. 

 9.49 

 9.54 

 9.43 

 9.53 

 9.69 

 10.53 

 10.72 

 9.70 

 9.47 



Chromium nitrate allowed a slight although appreciable dissolu- 

 tion of the iron base. With the possible exception of the case of 



"Burgess, C. F., Trans. Am. Electrochem. Soc. (1903), 4, 31, 



