On Zine Roofing. ——_ 
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 bea 
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 zinc 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 tigAt; 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 zine 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 zine roof tothe 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 zine, 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 
