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Page:Popular Science Monthly Volume 34.djvu/632

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men" ends with the production of the rough plate. Its next guardians bear the name of "grinders." These confer upon the glass the property of transparency. The grinding is accomplished by means of rotary grinding machines, the abrading material being common river-sand, dredged from the Alleghany. Several million bushels are annually required for this purpose. The plates are firmly fixed on rotary platforms by means of plaster of Paris, and rotating disks are so arranged that they cover the entire surface of the plate at each rotation of the platform. Small jets of water keep the grinding-sand constantly wet. But such treatment only removes the rough exterior; the smoothing is accomplished by means of emery, finer and finer grades being used as the process proceeds. The final polish is given by means of rouge (carefully calcined sulphate of iron), which leaves the glass perfectly smooth and ready for use.

Many doubtless remember the time—not so very long distant—when such a thing as American plate glass was totally unknown. It all came from France. But we have discovered—much to our satisfaction—that quite as good plate glass can be made at home as can be brought from across the water. Some, not as cautious as ourselves, say that the home product is the superior. Certainly the demand for it increases about as rapidly as new factories can be built to supply it. The joint product of the two Creighton plants is nearly two hundred and fifty thousand square feet per month, or about seventy acres of plate glass a year! It takes some eleven hundred hands to turn out such a product as this, and its value is reckoned in the hundred thousands. Natural gas is used everywhere throughout both works, displacing, perhaps six thousand bushels of coal daily. Among other duties, it supplies steam for engines of probably not less than three thousand aggregate horse-power. The new factory, some miles to the east of Creighton, will have a capacity, when completed, of three hundred thousand square feet of glass a month. We should hesitate to introduce so many figures, remembering the general aversion to statistics; but they will present, better than anything else, a just conception of the magnitude of the operations connected with a large factory, and will perhaps dispel the notion—if such exist—that we are still largely dependent upon French dexterity for our supply of plate glass.

Such, in brief, is an outline of the three processes by which a pane of glass may be produced. Each day it becomes more perfect, until now there seems little further to hope for, unless it be that the glass might lose some of its readiness to break into pieces on the least provocation. Our windows are already as large as we care to have them, and so clear that, every once in a while, some unlucky soul ignores the fact that the window has any glass in it.