188 



The Philippine Journal of Science 



1916 



Walker ^^ found that a galvanized- wire fence carrying 3.9 

 per cent of zinc was still in good condition after four years 

 of service, while another sample which carried 1.4 per cent 

 was badly rusted in three years. He makes the following ob- 

 servations : 



In every instance where a very durable fence was found, the coating 

 of zinc was relatively very thick; while on the other hand, the fences which 

 showed marked corrosion in from one to two years proved to have almost 

 no zinc on the iron, the zinc color being due to a layer of alloy alone. 



In accordance with the conclusions of other observers, and 

 from the results obtained, it is evident that in the manufacture 

 of galvanized sheets the application of the "maximum amount 

 of zinc consistent with the practical possibility of its man- 

 ufacture" ^^ should be striven for, if sheets are expected to render 

 long service on exposure. Economic and physical considerations 

 should be the limiting factors in deciding the minimum amount 

 of spelter per unit area. In recent years the tendency among 

 manufacturers to diminish the thickness of the spelter no doubt 

 has had an important bearing on the durability of modern corru- 

 gated sheets. 



Various standards of thickness of coating have been used, 

 among them the following: 



Table VI. — Va7-io7is standards of coating. 



Source. 



Kidder. 1913 edition, p. 1439 



American Civil Engineer's Pocket Book, 1913 edition, p. 393 



Standard Specifications of the Isthmian Canal Commission for 1909 



Trautwine, 1909 edition, p. 881 



Altoona car roofing, Proc. Am. Soe. Test. Mater. (1909), 9, 441 



Per 

 square 

 deci- 

 meter 

 (flat). 



Grams. 

 7.63 



16.58 

 7.63 

 4.88 



12.21 



Per 



square 

 foot 

 (flat). 



Ounces. 

 2.50 

 5.44 

 2.50 

 1.60 

 4.00 



The present work indicates that, for the Philippines at any 

 rate, 7.63 grams per square decimeter (2.50 ounces per square 

 foot) of spelter is the minimum coating for galvanized sheets 

 which will ensure satisfactory service. 



None of the other factors studied would account for the 

 differences in durability noted between old and new galvanized 

 iron. All sheets tested showed the presence of chlorides. The 

 lead found in the old and modern sheets is approximately the 



"Ibid. (1909), 9, 43. 

 ''Cuahman, ibid. (1909), 9, 143. 



