XI, A, 4 



Heise and Clemente: Galvanized Iron 



143 



respectively. These figures are equivalent to losses of iron 

 of 0.319 and 0.332 gram per square decimeter (0.105 and 0.109 

 ounce per square foot), with which the loss (0.11 ounce per 

 square foot) recorded by Witt ^^ for the same sample of gal- 

 vanized iron when stripped with hydrochloric acid is in good 

 agreement. There is always a layer of zinc-iron alloy formed 

 when iron is galvanized by the "hot process," whereas little " 

 or no ^* such layer is formed when iron is electroplated. There- 

 fore it is evident that the iron found in the stripping bath was 

 largely due to the zinc-iron alloy formed in the process of hot 

 galvanizing. 



As has been shoAvn (Table II), sulphuric acid alone can be 

 used for the analysis of galvanized iron with reliable results, 

 provided the acid is used in proper dilution. However, acid 

 strong enough to attack galvanized iron may be used success- 

 fully if electric current is used and the plate to be stripped is 

 made the cathode.^^ That the iron is protected from attack 

 by this method is shown by the data in Table V. 



Table V. — Stripping of galvanized iron with electric current; plate as 

 cathode. Size of plate, 8.8 by 3.8 centimeters {1.5 by 1.5 inches), except 

 as noted; bath, sulphuric acid; current, 0.75 to 1.5 amperes; voltage, S. 



Exper- 

 iment 

 No. 



Strength 

 of acid 



by 

 volume. 



Sample. 







Weight of coating. 



Loss. 



Per 



square 

 foot. 



Per 

 square 

 deci- 

 meter. 



48 

 49 

 50 

 51 

 52 



Per cent. 

 »2 

 b50 

 20 

 20 

 20 



Grams. 

 7.979 



Grams. 

 1.081 



Per cent. 

 13.55 



Ounces. 

 2.44 



Grams. 

 7.45 



8.285 



8.230 



= 16.387 



1.155 

 1.135 

 2.372 



13.94 

 13.79 

 14.48 



2.61 

 2.56 

 2.67 



7.96 

 7.82 

 8.17 



* Action is very slow, especially on side nearest anode. 



" No appreciable action in thirty minutes. 



= This plate was 3.8 by 7.6 centimeters (1.5 by 3 inches). 



Analysis showed that iron was also dissolved in this process. 

 The maximum amount determined in the solution was 0.047 

 gram. The agreement with our own previously recorded values 



" Loc. cit. 



^Walker, W. H., Journ. Ind. & Eng, Chem. (1912), 4, 397. 



" Bauer, loc. cit. 



"Reed, C. J., Trans. Am. Electrochem. Soc. (1907), 11, 181, recommends 

 the removal of mill scale from iron by making the iron the cathode in 

 sulphuric acid. 



