XX, A, 4 



Argiielles: Galvanized-iron Roofing 



183 



explains to a great extent the marked inferiority of some of 

 the latter. With the exception of brands G, A-2, and I, in- 

 dicated in Table III, the greater number of samples of modern 

 galvanized iron show less than 6.10 grams of coating per square 

 decimeter (2 ounces per square foot). Sheets of two brands, 

 "B" and "H," are definitely known to have failed in compara- 

 tively few years. It has been claimed that brand G gives 

 satisfactory service. As for the rest of the modern brands 

 very little information with regard to their durability is avail- 

 able. Actual weather-exposure tests over long periods of time 

 will be necessary to determine this point, although it is fairly 

 certain that those containing less than 6.10 grams of coating 

 per square decimeter will not withstand the weather for a con- 

 siderable length of time. 



IMPURITIES IN THE COATING 



The study of the impurities in the coating was confined to 

 the determination of lead, of the iron alloyed with the zinc, 

 and of the chlorides embodied in the spelter. The alloyed-iron 

 determination presents considerable difficulty in view of the 

 fact that part of the pure iron base is slightly attacked by 

 3 per cent sulphuric acid and that this attack differs widely 

 with different samples of iron. To determine the extent of the 

 solvent action of the acid, dezinced sheets of 7.62 by 10.16 centi- 

 meters (3 by 4 inches) were immersed in fresh standard acid 

 at 30 °C. for varying lengths of time. The results obtained are 

 shown in Table IV. 



Table IV. — Solvent action of 3 per cent sulphuric acid on iron base. 



[Figures give number of grams per square decimeter.] 



Brand. 



Weight 

 of sam- 

 ple. 



Loss on immersion after — 



1 



5 min- 

 utes. 



10 min- 

 utes. 



15 min- 

 utes. 



25 min- 

 utes. 



35 min- 

 utes. 



4 __._ 



F 



Grams. 



37.0028 

 35.4358 

 38. 1037 

 40. 4777 

 38. 4697 

 33. 1742 



Grams. 

 0.0328 

 0.0164 

 0.0116 

 0.0093 

 0.0094 

 0.0111 



Grams. 



0.0408 

 0.0216 

 0.0141 

 0.0096 

 0.0089 

 0. 0185 



Grams. 

 0.0491 

 0.0309 

 0.0302 

 0.0098 

 0. 0150 

 0.0167 



Grams. 

 0.0973 

 0.0581 

 0. 0229 

 0. 0119 



Grams. 

 0. 1369 

 0.1276 

 0.0363 

 0. 0138 

 0.0124 

 0. 0337 



H 



G 



I .._. 



8 



0.0486 





The foregoing table indicates the variation in the solvent action 

 of sulphuric acid which may be expected with different iron 

 bases. In actual determination of the spelter the sheet is not 

 allowed to stay in the acid more than five minutes after all 



142765- 



