248 Zinc, as a Covering for Buildings. 



Art. V. — On Zinc, as a Covering for Buildings ; in a letter from 

 Prof. A. Caswell to Messrs. Crocker, Brothers St Co. 



You some time ago requested me to examine an article on Zinc, 

 as a roofing material, published by Dr. Gale of New York, in a late 

 number of the Mechanics' Magazine. I regret that it has not been 

 in my power to give your request earlier attention. 



The remarks of Dr. G., which were copied by several papers at 

 the time, were fitted, in your opinion, to prejudice the public mind 

 unjustly upon a subject of great importance. He discourages the 

 use of zinc as a roofing material, upon several distinct accounts,. the 

 principal of which are the following. 



1. The difficulty of making the roof tight. 



2. The deterioration of the water vvhich falls from it. 



3. The comparatively small resistance which it offers to the pro- 

 gress of fire. 



1. As to the first of these objections, the brittleness of the metal 

 and its great expansion from heat are adduced, to show that a roof 

 cannot be made sufficiently tight. Zinc in the unwrought state is 

 well known to be very brittle, and there may be in the market rolled 

 or sheet zinc of a bad quality. But no one need be deceived on this 

 point, since nothing is easier than to test its flexibility. Sheet zinc 

 which will bear to be doubled and hammered down without any ap- 

 pearance of fracture in the bend, may be used as a covering for 

 buildings, without the least fear of leakage. Such is the fact with 

 regard to sheet zinc which I have examined from your manufactory; 

 and such, I am assured, is the fact with regard to foreign zinc from 

 the best manufactories. But any detailed examination of the brit- 

 tleness and expansion of zinc, so far as this question is concerned, is 

 entirely obviated by the well ascertained fact, that there is no prac- 

 tical difficulty in making a zinc roof perfectly tight. The numer- 

 ous certificates which you have submitted to my examination, from 

 most respectable gentlemen, who have made the experiment, place 

 the subject beyond all reasonable doubt. A zinc roof may as easily 

 be made tight as any other whatever. 



2. The second objection respects the deterioration of the water 

 which falls from the roof. This consideration is particularly impor- 

 tant to all those who are in the habit of using cistern water for culi- 

 nary and other domestic purposes. 



