On Zinc Roofing. 317 



market ? Has not " foreign zinc from the best manufactories" been 

 imported and tried in this city ? Yet all this avails nothing. So 

 long as zinc retains the name and properties of zinc, it will continue 

 to be a brittle metal, and though by heating it to a certain point, it 

 may be rolled into thin flexible sheets, yet, after a few years, the 

 metal becomes nearly as brittle as it was before being wrought. 

 This fact is a prominent one, not confined to zinc only, but is com- 

 mon to most other metals ; thus, malleable iron laid by for many 

 years, becomes exceedingly brittle, from a tendency in the metal to 

 assume the crystalline texture. I have observed fragments of sheet 

 zinc laid by for a number of years, become so brittle that they would 

 scarcely admit of bending without fracture. This seems to be a 

 general principle, and I have little doubt that it forms one of the 

 great difficulties in keeping zinc roofs in repair. Now if Prof. Cas- 

 well and Messrs. Crocker, Brother &; Co. have discovered that 

 there is no difficulty in making ziilc roofs perfectly tight, and that 

 their zinc " will bear to be doubled and hammered down without 

 any appearance of fracture in the bend," and that the same remark 

 is true of their zinc generally, 1 would advise them to come to New 

 York and teach our builders how to make zinc roofs tight ; for our 

 workmen are unable to do it, and consequently zinc has almost en- 

 tirely gone out of use for such purposes in this city. 



I did observe in my paper, that water drained from a zinc roof is 

 deteriorated, and thus is injured, either for washing or for culinary 

 operations. Now because the same properties are not noticed by 

 Thomson, Berzelius, Brande or Turner, Prof. Caswell has very ju- 

 diciously come to the conclusion, that such properties as I have attri- 

 buted to zinc cannot exist ; therefore, I must have been mistaken. 

 He also says I have not stated very fully the reasons on which my 

 opinion was founded, with regard to the oxidation of zinc on roofs 

 and the solubility of the oxide so formed, and as a proof that I was 

 mistaken he has exposed water from a zinc roof to the air in clean 

 glass vessels for several days, without any appearance of a precipi- 

 tate : he has also kept the water for several days in a vessel of oxy- 

 gen gas, subjected to frequent agitation, without precipitation or ap- 

 pearance of milkiness. Hence, he says, " if such water contains the 

 suboxide of zinc, its presence is not to be detected in this way." 

 The conclusion from the above experiment is, I think, very just, but 

 we shall see whether it will apply equally to my experiments, which 

 I shall now give in detail. They were made with a zinc roof, one 



