THE article on "The Action of Sunlight on Glass," published in The Popular Science Monthly for May, has elicited from Dr. F. Hollick, of this city, inquiries concerning the large plate-glass window of 104 Broadway, which is very much disfigured. Dr. Hollick says: "A 'Notice' was written on a piece of common brown paper, and pasted on the inside of the window with ordinary mucilage. On removing this 'Notice,' it was observed that the mucilage did not come off clean. Water, alcohol, and various other solvents, were employed, but all to no purpose, the glass remaining dim wherever the mucilage had been applied; the fact was, as was evident on inspection, that the surface of the glass was corroded, as if it had been acted upon by fluoric acid; and, what is more singular still, this corrosion has been extending ever since, till it now covers a large space. There seems to be a process of disintegration, or molecular change going on, which bids fair to destroy, in time, the whole pane. Now, the question comes, What is the nature of this change, and how was it started? The paper was of the ordinary brown wrapping kind, and the mucilage such as is in common use, and which has no action upon the bottle which contains it."
In reply to this inquiry, Mr. Thomas Gaffield, of Boston, writes:
To the Editor of the Popular Science Monthly.
Sir: A few days ago I received from a gentleman in New York some pieces of a large pane of plate-glass, taken from a window on Broadway, upon which had been affixed, with common mucilage, a notice written upon brown paper. When this notice was removed in about forty-eight hours, it was found that the portion of the surface covered by the mucilage was roughened, and presented an appearance of little hollows, or pits, from which the glass had been actually torn away by the washing or tearing off of the brown paper.
My informant says that some workmen passing by noticed the injured glass, and went in to examine it, stating that they had removed two other panes for the same defect. At the same time, experiments on other glass with similar paper and mucilage had led to no similar results, showing that all glasses are not so affected. My correspondent is surprised at what he has noticed, and desires an explanation of the cause. I will give my humble suggestions on the matter, and let others with more scientific knowledge enjoy the same privilege.
Let me at first, however, give a brief account of a few similar but very rare occurrences; for, though my New York friend names a fact not often noticed in the books, yet it is another illustration of the old saying, that "there is nothing new under the sun."
While spending some time, in 1862, in looking over the "Transactions" of the English and French scientific associations for one or two past centuries, I found the following very interesting item in the "Histoire de l'Académie," for 1708, page 22:
"A person having applied to a piece of glass, about six inches square, a paste of Spanish white and glue size, placed the whole in the sun, during the great heat of summer. The paste, which was turned toward the sun, having been heated, rolled itself up, so that, in its movement, its under side was raised upward. But, what was more singular, this surface raised with it, and carried away, a layer of the glass. This layer made on the paste a species of varnish, as of porcelain, the thickness not exceeding one-half a line. It was astonishing that the adherence of the paste to the glass was so strong; and equally so, that it should be able to detach from the glass so considerable a sheet. It had been blown, and apparently they had replunged the pipe, with which it was blown, in the crucible at different times, which had given it several layers, which, however, were not apparent, because they were exactly ap-