INGENUITY AND LUXURY 



THE COMPOSITION OF GLASS 



As is well known, silica is the chief component of 

 glass, and the mixture of this substance with other 

 substances in certain proportions determines the kind 

 of glass produced. "Potash or soda and lime 

 are mixed with the silica to obtain window or plate 

 glass," says Cochin; "add oxide of iron and you have 

 bottle glass; substitute oxide of lead and you obtain 

 crystal; replace by oxide of tin and you produce enamel. 

 The union of the fusible bases, lime, alumina, mag- 

 nesia, produce infusible compounds; but combined 

 with fusible and infusible bases, the silicic acid forms 

 multiple silicates which melt very readily. Plate glass 

 is precisely one of these mixtures of three elements. 

 It is composed of silica, soda, and lime, in the pro- 

 portion of silica 73, soda 12, and lime 15 parts. 



"Silica exists everywhere. Rock-crystal, sandstone, 

 sand, flint, are composed of silica; it is also found 

 in the ashes of plants, volcanic streams, and mineral 

 springs. Sugar resembles glass, and this likeness is 

 not deceptive. Melt the ashes of sugar-cane, and you 

 have glass; for with the silica they contain both potash 

 and lime. 



"Calcareous substances compose perhaps one-half 

 the crust of the globe. Lime is in our bones; it is also 

 in vegetables and straw, in the human skeleton and 

 common earth; it is found everywhere even more 

 widely distributed than silica. 



"Soda also is found in nature. It has long been 



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