318 On Zinc Roofing. 



hundred and eighty feet by ninety, equal to sixteen thousand two 

 hundred square feet, and repeated for three months, at every shower 

 of rain, and the effects produced by aUernate dryness and moisture 

 upon the metal were carefully noted. 1 cannot go into great mi- 

 nuteness of detail, but only sufficient to show the method of experi- 

 menting and the result. 



As soon as a shower of rain began to fall on the roof, some of the 

 first water that ran was collected and found to have a strong metallic 

 taste, and to decompose soap. The water was set aside and allowed 

 to remain at rest for some weeks, when a fine light yellowish sedi- 

 ment was found on the bottom. This effect was remarkably evident 

 in the cistern, where the metal was precipitated from a large body of 

 water. The sediment was carefully examined, and found to be oxide 

 of zinc. In many cases no sediment was obtained from water that 

 was examined, though collected in the early stages of a rain ; so 

 that no good results could be expected from a single experiment. 

 The greatest amount of sediment was produced from a fall of snow, 

 allowed to remain on the roof until removed by gradual thawing. 

 The water drained from the roof under such circumstances was 

 highly charged with metallic matter, which at length disappeared, 

 and a sediment of oxide of zinc was found on the bottom of the ves- 

 sel and the water left quite pure. Now as a metallic compound did 

 exist in the water, and as that, at length, disappeared by exposure, 

 and oxide of zinc was found deposited on the bottom of the vessel, 

 I inferred that the soluble compound was a suboxide of zinc, and 

 probably the one described by Berzelius. Since Prof. Caswell's 

 paper has appeared, I have called on a number of builders and 

 workers in metal, to ascertain whether and how far my experiments 

 and opinion, expressed in my paper in the Mechanics' Magazine, 

 coincided with facts as they occur to the workmen, and I am happy 

 to say that I have nothing to retract. The following corroboratory 

 remarks are from the Albany Daily Advertiser. 



" Zinc. — The experience of two winters has proved to our satis- 

 faction, that this is a worthless material for covering the roofs of 

 houses. It very soon becomes rotten, and, as it is put on, affords 

 very little protection against rain or snow. Tin or slate will be 

 found far preferable." 



In conclusion, I will again say, if zinc is a valuable material for 

 roofs, which can easily be made tight, why is it that the article is 

 going out of use as fast as possible ? Why is it that no new zinc 



