2. Mix intimately and as quickly as possible 1 part of pulverized pyrolusite, and 1 of zinc white with solution of water-glass to a plastic mass, which solidifies quickly. The power of resistance of this cement, it is claimed, is not inferior to No. 1, though experiments have proved No. 1 to be preferable.
CEMENTS FOR CHEMICAL APPARATUS.
Cements to be used for the above purpose must possess various properties difficult to combine in one preparation. They must be gas-proof, and capable of resisting the action of different vapors and acid fluids. As regards resistance to the action of chemical agents, there is nothing better than caoutchouc, but unfortunately it can only be used for tightening chemical apparatus not exposed to a high temperature.
In chemical laboratories bran of almonds, either by itself or kneaded with water to a thick paste, is frequently used, or rye or wheat bran mixed with a little flour and water. These cements, though very suitable for cementing glass distilling apparatus, are strongly acted upon by chlorine and the vapors of nitric acid.
For small apparatus to be used for the development of fluoric acid, plaster of Paris mixed with a little water can be used as a cement. To make the joint entirely gas-tight, paste a strip of paper over it. Although this cement does not resist the action of fluoric acid for any length of time, it suffices generally for the protection of the Workmen during the time the development of the acid is in progress, as, for instance, in chemical analyses, etc.
To cement chemical apparatus exposed to a temperature not exceeding 86° to 104° F. paraffine does excellent service; as it possesses the power of resisting the action of the strongest acids and alkalies.
Below will be found a few receipts for cements which have proved reliable.
Linseed oil and clay cement. Knead 10 parts of dry clay with 1 of linseed oil to a homogeneous mass. This cement will stand heating to the boiling-point of mercury.
Linseed oil, zinc and manganese cement. Knead 10 parts of pyrolusite, 20 of zinc white, and 40 of clay with sufficient boiled linseed oil (not exceeding 7 parts) to a plastic mass. This cement will stand a somewhat higher temperature than the preceding one.
Cements resisting very high temperatures. I. Clay 100 parts, powdered glass 2.