FIG. 1.—MODE OF USING THE CIRCLE DIVIDER.
The apparatus operates as follows: Suppose, for example, that it becomes necessary to divide a circumference into 19 equal parts: We make the aperture, C, coincide with the 19th division of the rule, and fix the point of the rod, T, in the center of the circumference, and cause the rule to revolve around it. The wheel, E, will revolve upon its axis, g, and, at every revolution, its point will make a mark which corresponds to the 19th part of the circumference—
Circumf. c / Circumf. C = r / R
It is always necessary that the extremity of the wheel, E, and the center-point, T, shall be at the same height in order to have the divisions very accurate.
FIG. 2.—THE CIRCLE DIVIDER.
SOLUBLE GLASS.
Although the manufacture of soluble glass does not strictly belong to the glass maker's art, yet it is an allied process to that of manufacturing glass. Of late soluble glass has been used with good effect as a preservative coating for stones, a fire-proofing solution for wood and textile fabrics. Very thin gauze dipped in a solution of silicate of potash diluted with water, and dried, burns without flame, blackens, and carbonizes as if it were heated in a retort without contact of air. As a fire-proofing material it would be excellent were it not that the alkaline reaction of this glass very often changes the coloring matters of paintings and textile fabrics. Since soluble glass always remains somewhat deliquescent, even though the fabrics may have been thoroughly dried, the moisture of the atmosphere is attracted, and the goods remain damp. This is the reason why its use has been abandoned for preserving theater decorations and wearing apparel. Another application of soluble glass has been made by surgeons for forming a protecting coat of silicate around broken limbs as a substitute for plaster, starch, or dextrine.