580 Mr. Warington on soine Specimens of Green Glass. 



to ascertain to what extent the foregoing glass differed from 

 our ordinary green glass of commerce, as occurring in the 

 form of wine bottles, an analysis of this was undertaken, and 

 the following are the results, calculated as before to the 100 

 parts : — 



Silica 59-00 



Lime 19*90 



Soda 10-00 



Potash 1*70 



Oxide of iron .... 7*00 



Alumina 1*20 



Magnesia 0-50 



Oxide of manganese ^ a trace 



99-30 



On comparing these results with the former, it will be seen 

 that the total amount of bases present is ftir less, and calcula- 

 ting them out as silicates, the first analysis will show a defi- 

 ciency of silicic acid amounting to about 20 parts on the 100. 



It was about the period of this examination being termi- 

 nated, that Professor Faraday, in a lecture at the Royal Insti- 

 tution on the manufacture of glass mirrors, exhibited a French 

 glass bottle which had been subjected accidentally by Mr. 

 Pepys, jun. to the action of diluted sulphuric acid, in the pro- 

 portions of 1 of acid to 10 of water; in a short time this had, 

 by its action on the glass, produced a most extraordinary and 

 beautiful crystallization of sulphate of lime in small, detached, 

 and rounded pyramidal masses, tightly adherent to the surface 

 of the bottle. Inconsequence of this curious action, I was in- 

 duced to submit the bottles under notice to a similar mixture, 

 and after having been filled and loosely corked they were put 

 aside in a place of safety. In the course of two or three 

 weeks I was surprised one morning to find the floor of the 

 laboratory covered with wet, which had apparently run from 

 the direction where these bottles had been deposited, and 

 on examination they were found to be cracked in all direc- 

 tions, the fissures being covered with a deposit of gelatinous 

 silica : on breaking one of these, the whole internal surface 

 was found lined, for the thickness of about one-fourth of an 

 inch, with a mixture of sulphate of lime and silica, the cry- 

 stallization of which had evidently caused the fracture of the 

 bottles ; in some places the glass was corroded completely 

 through its substance. 



