GLASS AND GLASS-MAKING 



manufactured in former years was the fact that so 

 little care was taken in properly apportioning the dif- 

 ferent ingredients, the mixing being largely a matter 

 of guess-work. But in the modern glass-factory this 

 haphazard method has entirely disappeared. The ex- 

 act chemical constituents of each ingredient are deter- 

 mined by analysis, and the proportions adjusted to a 

 nicety, with the result that there is now a great uniform- 

 ity in the product. 



As we have seen, when the various ingredients are 

 mixed together and brought to a certain temperature, 

 liquid glass results, a sirupy substance resembling 

 very thick molasses. Pouring this liquid upon some 

 flat surface in a thin layer and allowing it to cool, 

 would seem to be the easiest and most natural method 

 of making such flat sheets as window glass. And, 

 indeed, such a method is the one now used for making 

 the superior quality of window glass, or plate glass. 

 This is not the method, however, by which glass of 

 inferior quality is manufactured. Ordinary window 

 glass, for example, is blown first into hollow cylinders, 

 then smoothed and flattened out. This process is a 

 much more picturesque one than that used in making 

 plate glass, although the product is greatly inferior. 



THE PROCESS OF MANUFACTURING WINDOW GLASS 



The mixture of soda, lime, and silica that is to be 

 melted and transformed into glass is technically known 

 as the ' ' batch. ' ' The melting and transforming processes 

 are slow and tedious ones consuming many hours, and 



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