The glass melts on exposure to great heat and slags the clay to a hard mass. The same effect is produced by adding small quantities of soda and borax to the clay. An admixture of chalk and boric acid, as in the following receipt, also gives excellent results.
II. Clay 100 parts, chalk 2, boric acid 3.
Cement resisting acids. Melt rubber with double the quantity of linseed oil, and then knead in sufficient bole to form a paste. This cement resists the action of nitric and hydrochloric acids, and can be advantageously used for closing bottles containing them. As it solidifies very slowly, it can readily be detached from the bottles, and used again.
For cement which is to solidify quickly on exposure to the air, add a few per cent. by weight of red lead or litharge.
Rubber cement for chemical apparatus. Cut 8 parts of rubber in small pieces and throw them gradually into a mixture of 2 parts of tallow and 16 of linseed oil previously strongly heated. After effecting an intimate mixture of the constituents by vigorous and constant stirring, add 3 parts of white bole.
Although this cement does not stand a high temperature, it possesses an extraordinary power of resisting the action of acid vapors.
Scheibler’s cement for chemical apparatus. Melt together 1 part of wax and 3 of shellac, and work into the mixture 2 parts of gutta-percha cut up in very small pieces. This cement will bear considerable heat without actually melting.
CEMENTS FOR SPECIAL PURPOSES.
Cement for attaching metal letters to glass, marble, wood, etc. Dissolve over a water-bath 5 parts of glue in a mixture of 15 parts of copal varnish, 5 parts of boiled linseed oil, 3 parts of crude oil of turpentine, and 2 parts of rectified oil of turpentine, and add 10 parts of slaked lime to the mixture.
Cement for joints of iron pipes. Mix 5 lbs. of coarsely powdered iron borings, 2 ozs. of powdered sal ammoniac, and 1 oz. of sulphur with sufficient water to form a paste. This composition hardens rapidly, but if time can be allowed it sets more firmly without the sulphur. It must be used as soon as mixed, and rammed tightly into the joint.