XI, A. 4 Argiielles: Galvanized-iron Roofing 189 



same when calculated on the basis of spelter content, and 

 probably in no case was it high enough to affect durability 

 adversely. The iron dissolved by 3 per cent sulphuric acid 

 assumed to represent the iron alloyed with zinc is approximately 

 the same in the old and modern sheets when calculated on the 

 basis of spelter content. Modern sheets are not inferior with 

 respect to continuity and ductility of coating as compared with 

 the old sheets. The iron body of modern galvanized sheets is 

 of high purity and is equal or superior in quality to that of 

 old sheets. 



SUMMARY 



The importantion of galvanized-iron roofing to the Philippines 

 approximates 1,500,000 pesos in value annually. Many of the 

 recently imported brands fail rapidly, while certain brands have 

 given satisfactory service for over thirty years. 



Of the various factors influencing the durability of galvanized 

 iron which have been studied with a view toward accounting 

 for the difference in behavior of old and modern sheets, it 

 appears evident that the greater weight of zinc per unit area 

 on the former accounts for the greater durability. The modern 

 sheets were not inferior to the old product with respect to 

 the presence of impurities in the coating or in the iron base or 

 with respect to continuity, ductility, or toughness of coating. 



For satisfactory service in the Philippines, galvanized iron 

 should have a coating of not less than 7.63 grams per square 

 decimeter (2.50 ounces per square foot). 



The advanced corrosion often noted in the Philippines of 

 sheets newly arrived or kept in storage probably finds explana- 

 tion in the fact that galvanized iron corrodes very rapidly when 

 continually kept moist either by actual contact with water or 

 by the presence of damp air. 



Proper paints, applied after the surface of sheets has become 

 well roughened by exposure, will greatly increase the life of 

 modern galvanized iron. 



