Popular Science Monthly/Volume 31/June 1887/Grains of Sand
|GRAINS OF SAND.|
By GEORGE WARDMAN.
THE manufacture of sand is an important industry, which has Pittsburg for its headquarters, although the sand is not made within the limits of the city. There is a considerable traffic in Monongahela sand, which is scooped up from the bed of the river, to be used for common building purposes; but the manufacture of sand is quite another affair, and the product goes into quite a different commodity, which is glass.
Practically glass is almost pure sand, other substances used in its manufacture for fluxing being consumed while the sand is transformed to a greater or less degree of transparency. The sand used in glass-making is almost pure silica, so nearly pure that there is less than one per cent of iron, magnesia, and aluminum, to ninety-nine + per cent of the other. And of this sand, which is quarried out of the hills and ground down to varying degrees of fineness, and washed to varying degrees of whiteness, eight hundred tons are manufactured daily, four hundred tons being consumed in and about Pittsburg, and four hundred tons going into Eastern Ohio and West Virginia to Wheeling, Bellaire, Columbus, and all points within a circuit of one hundred and fifty miles from Pittsburg.
In selecting, a darkish sand is found, containing more foreign substances than the ninety-nine per cent silica, which inferior grade goes into green or "black" bottles, and a still darker and baser earth, which is used for sanding fire-brick molds; another and finer dark grade, which is used by crucible-steel manufacturers; and still another quality, the whitest and grittiest, which becomes "flint," or what might be called absolutely transparent glass. An inferior quality of white sand is used for prescription-bottles, but the very best is for the higher grade of flint-ware.
Looking through the flat surface of window-glass, whether plate or blown, it appears colorless; but, if the sight is directed through the edge, it will disclose a sea-green tinge. Flint-glass proper is not so. It is absolutely colorless, except when cut into faces or prisms, when it reveals the colors of the spectrum.
The cost of a ton of sand to glass-manufacturers of Western Pennsylvania, Eastern Ohio, or West Virginia, is, of course, dependent on the distance it is hauled from the quarry; but, taking the eight hundred tons daily manufactured and consumed, it will not average above $2.25 per ton, damp. Dried sand will average $2.50 per ton. Of course, it costs a little less than those figures in Pittsburg, and a little more in Bellaire, Ohio; but even at this last-named place, the cost of the sand which goes into the manufacture of a box of common window-glass, containing the regulation fifty square feet of surface, is about five cents; that is, the box of glass consists merely of five cents' worth of silica, transmuted to a state of transparency.
The sand used in the glass industry in Western Pennsylvania, Eastern Ohio, and West Virginia, comes from three quarries: one on the Pennsylvania Railroad, overlooking the Juniata; one on the Baltimore and Ohio Railroad, near Connellsville; and one on the Pittsburg, McKeesport, and Youghiogheny Railway, twenty-five miles south of Pittsburg. It is quarried out like building-stone, passed through a quartz-crusher, further reduced under immense iron wheels, and finally ground and washed in an endless screw. The washing releases some of the foreign substances, but streaks of iron which are sometimes found running through the stone are knocked off to undergo the milling process for the inferior quality of sand, some of which goes into mortar for specially fine and durable wall-building. The rail-roads use large quantities of it in the construction of retaining-walls for embankments. And so all grades of the sand are utilized.