Glass Paper

Sandpaper a3 now made is false to its name, for it has no sand about it, the place of that material belng - now taken usually by powdered glass. which does its work with vastly greatei effect. One of the most important operations in the fabrieation oí sandpaper is the pulverization of the glass Into powder of the different grades of flneness. Commonly an iron mortar is used for this purpose, a heavy iron pestle being the crushing instrument. Stamping machinery is better. It consists of a stout box, whose iron side walls serve as a base for the stamping machinery. In the box, which can be closed by a wooden door to prevent waste of material and also injury to the workman, are two iron cylinders in which play the stamps. These crush the glass, turning on their own axles as they work. For grading the powder several shifting cylinders are necessary, covered with gauze of different mesh. Beginning with the coarsest the workman proceeds gradually to the finest, resifting each time that which passes through the network. The paper to be used in the manufacture must be good, strong, and rather long fibred; it must also be frse from knots and irregularities, and if there be any such they must be planed off. If they should be overlooked, they would interfere with the proper use of the sar.dpaper; the knots would protrude through the glue, and little ridges and channels would result, making it impossible to smooth off a surface evenly with the paper. The paper is cOt into large sheets, spread on work table3, fastened down, and then painteJ, by means of a large brush, with a thin, even coat of hot glue. Iï the glue is too thin and the paper of bad quality, the glue soaks into tho paper, so that which remains is not of sufflcieat consistency to hold the glass. Thus results a sandpaper from which the glass easily rubs off, or which, in places. h?s no glass at all, or not enough. This is notably the case with the coarser varietles, in which tho layer of gli;e must be put on with exceedingly care that the relatively large fragments of glass, which can in no manner be soaked with the binding material, may be held fast in it. On the other hand, if the layer of glue is too thick or the consistence too viscous, the outer part hardens too quickly, so that the glass powder cannot mbed itself in it.