THE TESTING OF GALVANIZED IRON ^ 



By J. C. Witt 



{From the Laboratory of General, Inorganic, and Physical Chemistry, 



Bureau of Science, Manila, P. I.) 



TWO TEXT FIGURES 

 INTRODUCTION 



There are four general methods for galvanizing ^ — namely, 

 hot galvanizing, electrogalvanizing, sherardizing, and cow- 

 perizing. The essentials of each are briefly as follows : 



Hot galvanizing. — This process was patented by Crawfurd * 

 in 1837. The iron is first cleaned in dilute hydrochloric or sul- 

 phuric acid, washed in water, and then passed into a bath of 

 molten zinc. The temperature is usually kept as low as possible 

 to avoid too much volatilization of the zinc and too great a loss 

 from alloying with the iron. Excess zinc is removed either by 

 passing between rollers or by shaking or centrif uging. The 

 process is economical in time, but wasteful in zinc. According 

 to Tumbull * the distribution of zinc in a hot galvanizing bath 

 is as follows : 



Per cent. 

 Coating on the articles 68 



Dross 18 



"Ashes" 12 



Volatilized 2 



Electrogalvanizing. — After being thoroughly cleaned, the iron 

 is placed in a solution of a zinc salt and the zinc is deposited 

 by electrolysis. The anode is usually lead or zinc. This process 

 is extensively used for small objects, such as bolts and nails, 

 and also for boiler tubes. 



Sherardizing. — In this method the iron is cleaned and placed 

 in a large iron drum which contains zinc dust. The drum is 

 then heated to a temperature of from 260° to 315°C. The con- 

 tainer should be air-tight, and most of the air should be removed 



' Received for publication November 24, 1915. 



'See Sherard Cowper-Coles, Electrochem. & Met. Ind. (1908), 6, 189. 

 ' Thorp's Dictionary of Applied Chemistry. Long-mans, Green, & Co., 

 London (1913), 5, 810. 



Woum. Inst. Metals (1914), 12, 301. 



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