GLASS-MAKING. 603 



the other hand, the processes of maiiufacture by which the latter 

 glass is produced have been so far perfected that its use is now 

 permitted to many who would hitherto have thought themselves 

 unable to afford it. 



A third form of window glass, the so-called crown glass, must 

 also be mentioned for the sake of completeness, though it has 

 little commercial importance, and less in America than in Eng- 

 land. Both sheet and crown glass owe their origin to the blow- 

 er's breath. Though they are less brilliant than the plate, their 

 methods of fabrication are much toore interesting, since they in- 

 volve a far greater amount of manual dexterity on the part of 

 the artisans. It is, indeed, difficult to know which to admire the 

 more, the chemistry or the physics of the operation ; the nicety 

 with which the glass-maker regulates the proportions of his 

 charge so as to produce this beautifully clear substance, or the 

 skill with which he subsequently handles the finished glass ard 

 adapts it to our uses. 



Sheet glass forms the window-pane of the multitude. The 

 possibility of making it of excellent quality and in large sizes 

 is due almost entirely to the substitution of gaseous for solid 

 fuel. No other among our numerous American industries has 

 been so benefited by the utilization of natural gas. European 

 sheet glass was up to this time unquestionably superior to our 

 own. A larger experience and more approved furnaces made it 

 possible for the foreign manufacturers, and particularly those of 

 France and Belgium, to solve with greater success the knotty 

 problems connected with glass-making. In many places they had 

 already substituted gas for coal, and obtained the happiest results. 

 With the advent of natural gas the position of the American pro- 

 ducer was suddenly changed. He had at his command the most 

 desirable of fuels, and one that was at the same time very cheap 

 and almost totally free from sulphur. As a result, he soon equaled 

 and now surpasses his transatlantic rivals. 



But the manufacture of window glass is essentially difficult. 

 Even when the troublesome question of fuel has been satisfacto- 

 rily settled, there remain many other substantial difficulties which 

 must be met and conquered. From the mixing of the crude ma- 

 terials to the annealing of the finished product, the glass-maker 

 must be alert and intelligent. It is a very easy matter simply to 

 make glass. Sand, metallic bases, and heat are the only elements 

 needed. But to make good glass — glass that is clear, transparent, 

 colorless ; that simulates the purest water of a mountain-stream — 

 this requires skill and patience. From beginning to end the pro- 

 cess is one of painstaking and delicate manipulation. 



In the genesis of a pane of glass, the first step is naturally the 

 provision of such stuff as it is made of. While glass is theoreti- 



