XI, A, 4 Argiielles: Galvanized-iron Roofing 185 



less lead per square decimeter than the old, the lead content, 



expressed as r — -. — > was about the same for both, in no 



per cent zmc 



case exceeding 1 per cent. It is scarcely probable that its 

 occurrence in either the new or the old sheets was a very im- 

 portant factor in determining durability. For the majority of 

 the modern galvanized sheets the alloyed iron is considerably 

 less in amount than for the old sheets, averaging about 0.2 

 gram per square decimeter for the former and about 0.3 

 gram per square decimeter for the latter. When calculated to 



per cen iron ^j^^ greater number of both kinds of sheets 

 per cent zmc 



give results ranging from 3 to 4 per cent. The maximum for 

 old sheets was 5.32 per cent; the highest among the modern 

 sheets were 10.42 and 5.48 per cent. 



Tests for chorides in the sheets analyzed showed the presence 

 of perceptible amounts in all cases, so that no difference in 

 durability could well be ascribed to that cause. 



IMPURITIES IN THE BASE 



In recent years certain manufacturers have been using iron 

 of exceptional purity, several brands analyzed in this laboratory 

 showing only between 0.20 and 0,40 per cent impurities. So far 

 as length of service of the galvanized sheets under investigation 

 is concerned, the purity of the iron base has been a factor of 

 minor importance and higher impurities than those found in 

 modern sheets have not prevented long service. 



PHYSICAL CHARACTERISTICS 



With few exceptions, the modern sheets examined have been 

 found to be free from physical defects, thus bearing out the 

 observation made by Walker ^^ on hot-galvanized ware in general 

 They were, on the whole, fairly ductile, free from cracks and 

 pinholes, and showed no marked brittleness. The old galvanized 

 sheets have been found to be slightly less ductile, due to thicker 

 spelter and to oxidation undergone during long years of weather 

 exposure. 



CORROSION OF UNUSED SHEETS 



Considerable trouble has been experienced in the Philippines 

 with unused sheets of imported galvanized iron which showed 

 advanced stages of corrosion, either upon their arrival in Ma- 

 nila or after short storage periods. In some cases there was 



"Proc. Am. Soc. Test. Mater. (1909), 9, 436. 



