XI. A. 4 Witt: Testing of Galvanized Iron 149 



binding alloy is present even in iron that has been electrogal- 

 vanized or sherardized. In hot galvanized iron, crystals of 

 FeZn., and FeZn. have been found. 



VARIOUS METHODS OF TESTING 



A number of methods have been published for determining the 

 amount of zinc coating on galvanized objects. Among them may 

 be mentioned the amalgamation method and the use of solutions 

 of copper sulphate, sodium hydroxide, lead acetate, etc. The 

 various tests may be divided into two groups : 



1. The galvanized object is placed in a solution which will 

 attack the zinc, but has little effect on the iron base. After 

 a given period of time it is removed, cleaned of any loosely 

 adhering substances, and again placed in the solution. The 

 strength of the solution is known, and the temperature is kept 

 within certain limits. When all the zinc is removed at any 

 point, the test is regarded as complete, and the number of 

 immersions are recorded. 



2. All the zinc is removed. The weight per unit area or 

 unit length is calculated. 



A test of the second group is to be recommended whenever 

 practicable. Such a test is now almost universally used for 

 galvanized sheets and is well adapted to wire. Tests of the first 

 group are usually applied to all irregular objects such as bolts 

 and nuts. Specifications are written on that basis, and consid- 

 erable work would be required to determine just how much 

 coating should be found on all the various articles that are now 

 galvanized and to rewrite the specifications. However, it seems 

 likely that this will be done in time and that all tests of the first 

 group will go out of use. 



The amalgamation, or mercury, method seems to have been one 

 of the earliest used. Warren * found that by putting a clean 

 galvanized object into mercury all the free zinc was removed. 

 The zinc, which was alloyed with iron, combined with mercury, 

 also, in the ratio of 7:11. This new alloy could then be volatil- 

 ized in a nonoxydizing flame and the zinc calculated and added 

 to that previously removed. Of course, this procedure would not 

 be satisfactory for routine work. 



Sodium hydroxide solution is sometimes used for removing 

 the zinc from galvanized iron. This method is not satisfactory 

 because it is slow and because some of the zinc-iron alloys are 

 not attacked. 



' Loc. cit. 



