(1) Simply pure white lead ground in oil, and used very thick, is an excellent cement for mending broken crockery ware; but it takes a very long time to harden sufficiently. The best plan is to place the mended object in some store-room, and not to look after it for several weeks, or even months. After that time it will be found so firmly united that, if ever again broken, it will not part on the line of the former fracture. It resists moisture, and a heat not exceeding that of boiling water. (2) White lead, ground in oil, a sufficient quantity; add dry red lead enough to make a stiff putty. Put the mass in a mortar or on a block of iron or smooth stone, and pound it till it becomes soft; continue to add red lead, and pound until the mass will no longer become softer by pounding, nor stick to the fingers. At this time it should be of sufficient tenacity to stretch out 3 or 4 in. when pulled, without parting. The more protracted the pounding, the softer, finer, and more tenacious the cement becomes. Interpose this putty between the flanges of steam-pipe joints, taking care to put a thin grummet of packing or wicking around the diameter of the bore, to keep the cement from squeezing through when the flanges are screwed together.
It is indestructible by steam or water, and makes the best joint known to the engineer. (3) Mix 2 parts finely powdered litharge with 1 of very fine sand, and 1 of quicklime which has been allowed to slake spontaneously by exposure to the air. This mixture may be kept for any length of time without injuring. In using it, a portion is mixed into paste with linseed oil, or, still better, boiled linseed oil. In this state it must be quickly applied, as it soon becomes hard. (4) Mohr's. Equal parts litharge and brickdust made into a paste with linseed oil, applied, and a little sand dusted over. (5) Serbat's. Sulphate of lead calcined and ground, 72 parts; peroxide of manganese, 24 parts; linseed oil, 13 parts; intimately mixed. This lute is soft, and will remain in that state indefinitely. For use, it only needs to be rubbed up between the hands. It may be advantageously employed in boilers, steam engines, etc.; it sets perfectly, and does not soften under the influence of heat, but, on the contrary, becomes very hard, especially if care be taken to pass a hot iron over the joints. A sudden leak may be stopped immediately, by applying some of this lute under a hot iron.
It is preferable to red lead.