626 



THE POPULAR SCIENCE MONTHLY, 



to the chemical interchange called isomor- 

 phism, giving up its potash for some of the 

 soda in the glass. These new compounds, 

 if soluble in water, would be removed in 

 washing off the mucilage, or, if insoluble, 

 would be torn away when pulling off the 

 paper attached by the adhesive gum. 



In view of these facts, it would be well 

 not to run the risk of possible injury to any 

 of our valuable windows by affixing notices 

 upon them with mucilage. 



My correspondent thinks he noticed a 

 continued or increasing corrosion, or dis- 

 integration, of the surface of the plate- 

 glass after the removal of the mucilage. 

 On examination of one of the pieces sent 

 to me, I found a discoloration, occasioned 

 by what we call " rust," in a part not affect- 

 ed by the mucilage, and this was probably 

 what our friend observed. 



There are glasses sometimes made with 

 an excess of uncombined alkali which ef- 

 floresces upon the surface, sometimes be- 

 fore it is placed in the window, and some- 

 times at a later pe«-iod. This, of course, 

 causes a series of infinitesimal holes or fur- 

 rows in the glass, whose surface by the re- 

 flection and refraction of the rays of light 

 presents, like the mother-of-pearl, all the 

 colors of the rainbow when held in a cer- 

 tain position, and at the right angle for such 

 effect. This is one kind of what is called 

 stained or rusty glass. In other specimens 

 the disintegration goes beyond the infinitesi- 

 mal character and is plainly visible, making 

 the glass appear as if fire-cracked, and in 

 its ultimate effect producing the appearance, 

 on one or both surfaces, of ground glass. 



In one of these stages of rust or disinte- 

 gration I find a piece of the glass referred 

 to by ray correspondent. 



In reference to the matter of rust on 

 glass, for the comfort of my readers and of 

 my New York friends who are dealers in 



window-glass (which was my business for 

 many years), let me say that this difficulty 

 or defect is not an every-day trouble, but 

 only one of the incidents or curiosities of 

 glass-making. A good glass-maker knows 

 how to avoid it, and a good glass-dealer can, 

 in many instances, remove the first appear- 

 ance of rust or stain on plate or sheet glass 

 by a skillful and nimble use of dilute hydro- 

 fluoric acid and rouge or oxide of iron. 



Glass -making and glass -deahng have 

 their troubles, and this of occasional rust 

 on glass is one. But all other kinds of 

 business have their trials, and they all have 

 their points of interest and satisfaction. In 

 the study necessary to remove troubles and 

 avoid mistakes, comes half the pleasure of 

 life. If we had no obstacle in the path of 

 our business, we ourselves would rust out. 



In closing my article, let me add that I 

 give my opinions only as humble sugges- 

 tions, after such examination as I have been 

 able to give to the subjects referred to. 



In the light of hew experiments, and 

 the progress of scientific research by those 

 who make it the business of life, the theo- 

 ries of to-day may be set aside by the reve- 

 lations of to-morrow. If "an undevout as- 

 tronomer is mad," so must be an undevout 

 chemist, or student in any domain of natu- 

 ral science, who will not humbly bow before 

 the wise and wonderful workings of the 

 Great Maker of the universe. We cannot 

 fully understand or explain them now. We 

 can only look " through a glass darkly." We 

 can see and enjoy the light of the sun, but, 

 though great and learned volumes be writ- 

 ten, who can fully explain all the laws and all 

 the wonders of light, one of the gentlest and 

 most ethereal, and yet one of the most in- 

 teresting and powerful elements of the uni- 

 verse ? We must be content to labor and 

 to wait. 



Boston, July 20, 1874. 



EDITOR'S TABLE. 



THE DUST OF THE UNIVERSE. 



THE comet has come and gone, and 

 again raised the perplexing ques- 

 tion as to what such bodies are made 

 of, and what are the most subtile 

 forms of matter diffused through the 



celestial spaces. Of the great moving 

 masses which compose our own sys- 

 tem, from the sun — 1,000,000 times 

 larger than the earth — to the little 

 asteroids — 250 miles in diameter — and 

 from these down to the meteorites 



