62< 



THE POPULAR SCIEXCE MONTHLY. 



CORRESPONDENCE. 



CTJPwIOUS ACTION OF MUCILAGE OX 

 GLASS. 



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 dis- 

 figured. Dr. Hollick says : " A ' Notice ' 

 was written on a piece of common brown 

 paper, and pasted on the inside of the win- 

 dow with ordinary mucilage. On removing 

 this ' Notice,' it was observed that the mu- 

 cilage did not come off clean. Water, alco- 

 hol, and various other solvents, were em- 

 ployed, but all to no purpose, the glass re- 

 maining 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 disintegra- 

 tion, 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 wrap- 

 ping 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 win- 

 dow 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 wash- 

 ing or tearing off of the brown paper. 



My mformant says that some work- 



men 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 corre- 

 spondent 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 " His- 

 toire de I'Academie," for 1708, page 22: 



" EXFOLIATED GLASS. 



"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 lipe. It was aston- 

 ishing 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- 



