A Hot Wire Cutter for Glass Tubing A . A HIRSCH' Sewerage and Water Board, New Orleans,
La.
A
N E X T R E M E L Y simple glass cutter, by which pressure of a glowing wire looped around the glass shape is secured by means of suspended weights, is shown in the figure. This device produces clean breaks and is instantly adjustable to a n y size of glass tubing or bottles. Current is supplied through a lamp bank to binding posts on the 350-gram brass weights, W , which hang from the ends of the resistance wire, R. R is looped once around the object to be cut, thereby making one and a half turns in contact with the glass. Porcelain beads, B, such as are used on commutator brush leads, are strung on the wire to separate the adjoining arcs and to provide thermal insulation on the redundant half turn. When using No. 25 B.W.G. Nchrome or Chrome1 A resistance wire about 100 cm. long, 1000 watts' load in the lamp bank connected t o the 110-volt house circuit produces a complete circumferential crack in largediameter ordinary glass tubing within a minute of heating. A file scratch made a t the top of the tube where the two wire segments approach uninsulated contact tends t o guide the cut. 1 Preeent address, Louisiana Department of Education, Division of Trade and Industrial Education, Baton Rouge, La.
An Improved Magnesite Crucible WELTON J. CROOK, JOHN R. CUNNINGHAM, AND JAMES R. CADY Stanford University, Calif.
Previous Investigations
A new method of producing magnesite
. crucibles for laboratory purposes is pro-
A considerable amount of work has been done on the subject of the production of magnesia crucibles for laboratory use. A study of the literature reveals t h a t the method of procedure varies in only two general respects-namely, the binders used t o hold the unfused magnesia and the temperature at which the molded crucibles are fired.
posed. The base material is crushed magnesite brick which is sintered at 2000' C. in a graphite mold placed in a high-frequency furnace. Crucibles made in this manner have been found to be impervious to liquid basic slags which not only permeate but actually disintegrate commercially available magnesia and magnesite crucibles.
Jordan, Patterson, and Phelps (2) moistened < 100-mesh dead-burned magnesia with a 2 per cent magnesium chloride hexahydrate solution, molded this material into graphite molds and, after drying the molds containing the crucibles, fired them a t from 1600" to 1800" C. Swanger and Caldwell (6) used the same procedure, but added less moisture and obtained an equally satisfactory crucible. Salmang and Planz (4) used a much higher proportion of magnesium chloride, and found that denser crucibles were obtained when carefully sized magnesia was used. Mehl (3)mixed shellac with calcined c. P. magnesia and molded the crucibles in a brass mold. The crucibles were then dried a t from 100' to 130" C., and fired in an electric furnace. Schuette (5).tamped 200
