Cements glycerol-litharge

It is quite necessary that the welding of the tank is perfect and free from pin holes. Leaks frequently appear where the tubes are welded in the top of the tank. These may be eliminated by brazing the joints. A less satisfactory way is to use a cement of litharge and glycerol. This cement may also be used with success on leaky valves. Occasionally leaks occur in the rubber tubing or its connections with the bottle or tank, but these are unusual. 

A somewhat crude though convenient classification can be made on the basis of the principal ingredients, thus. (1) Portland cement, (2> high alumina cemenl. (3) sodium silicate. (4 magnesium oxychloride plus copper powder, (5) litharge or red lead plus glycerol. (6) rubber latex, and (7) synthetic resins. Supplementary materials to be considered are asbestos, white lead, plaster of Paris, sulfur, graphile, sand, pilch, tar, rosin, and boiled linseed oil. 

Fluorinated hydrocarbons of fatty consistency can be used for lubricating metal surfaces and taps, with an external seal of piceine. Packing rings of lead, soft iron, or copper are used when connecting metal apparatus. Litharge in glycerol is a suitable cement. 

The resultant HF still contains traces of entrained KF and can be redistilled at 30-35°C into the second receiver. For very pure HF, silver equipment should be used [2Q. Since organic substances are immediately decomposed by HF vapor, joints can be made tight only by means of the Cu cones described. Alternatively fused sulfur may be used, with picein or a like substance covering cracks in the sulfur mass. As a temporary expedient, resulting in not quite anhydrous acid, the seal can be made with well-dried litharge-glycerol cement. 

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