148 The Philippine Journal of Science isie 



to prevent much of the zinc from oxidizing. The thickness of 

 the coating depends on the time and the temperature. 



Cowperizing. — The iron is placed in a drum made of wire 

 netting and is treated with zinc vapor in an atmosphere of 

 hydrogen. The reducing action of the hydrogen aids in keeping 

 the zinc free from oxide and thus insures a good adhesion of 

 the deposit. This process is especially suitable for coating 

 articles which have threads or which require to be accurately 

 fitted, because the zinc is evenly distributed. 



Only the hot galvanizing and the electrogalvanizing processes 

 are used in the manufacture of galvanized sheets. The present 

 work has been done with sheets galvanized by the former 

 method. 



The question of galvanized sheets is of importance in the 

 Philippine Islands. They are extensively used as a roofing ma- 

 terial to replace nipa. They are light and, of course, not in- 

 flammable. About 80 to 90 per cent come from the United States 

 and are bought under the specifications that for each 900 

 square centimeters there must be a minimum of 54.9 grams of 

 coating (two ounces per square foot).^ It seemed advisable to 

 investigate various methods of determining the amount of the 

 coating and to decide if possible which is the best with reference 

 to accuracy and the time, labor, expense, and other factors of 

 applying it. 



In this connection the structure of galvanized iron is of 

 interest. There is no sharp line of demarcation between the 

 iron base and the zinc coating, but between the two is a series 

 of zinc-iron alloys. The alloys nearest the iron base contain 

 mostly iron. From this outward there are other alloys, each 

 with a lower percentage of iron, till the zinc itself is reached. 

 Warren" expresses the relationship very clearly when he says: 

 "Zinc in galvanized iron exists in two states. (1) Part of the 

 zinc forms an alloy with the iron (2) zinc adheres to this alloy 

 mechanically." 



Arthur and Walker'^ have made a study of the structure of 

 galvanized iron by microscopic methods. They state that the 



' In the United States, tests on galvanized iron are reported in terms of 

 ounces of zinc per square foot. In order that this paper may be easily 

 compared with others on the subject, results are given in both systems of 

 weights and areas. 



'Phil. Mag. (1871), IV, 41, 132. 



' Journ. Ind. & Eng. Chem. (1912), 4, 397; see also v. Vagesack, Zeitschr. 

 f. anorg. Chem. (1907), 52, 30. 



