We have described, at page 52, the method of refining lead for obtaining the silver which it usually contains, by which process there results an oxide of lead, called litharge. The use of this substance for making oil and oil paints dry sooner is well known; it remains to be observed in this place, that it is the material from which red lead is made. The litharge is put into pots, and exposed to the action of flame in a reverberatory furnace for forty-eight hours, during which time it is frequently stirred; hence it acquires the orange-red colour, termed minium, or red lead. There are other modes of obtaining red lead. In Germany and some other places, metallic lead is calcined on the hearth of a cupola furnace, and constantly stirred for eight hours; then left in the furnace for sixteen hours more, stirring only at intervals. The massicot thus produced is then ground in a mill, washed, dried, and put into earthen pots, so as only to make them about a quarter full, in which they are exposed to the action of flame, enveloping them in a furnace for forty-eight hours, by which time, the colour being fully developed, the pots are taken out, and their contents passed through sieves to separate any foreign or gross matter.
Turner's Patent Yellow, now almost entirely disused, may be obtained by pouring upon litharge, one-third of its weight of muriatic acid, and, after letting it stand for twenty-four hours, melting the whitened litharge, by which it becomes yellow. Goulard's extract is made by boiling litharge in vinegar.