292 



LEAD. 



white carbonate, and chromate of potash will throw down a beau- 

 tiful orange-yellow powder. When the presence of any of the 

 oxides or salts of this metal are suspected in a dry substance, 

 it may be reduced to a metallic state by subjecting it to the action 

 of heat by means of a blow-pipe upon charcoal. For an account 

 of several ingenious processes for discovering the presence of this 

 metal in mixed fluids, the reader may consult Dr. Christison's 

 valuable "Treatise on Poisons." 



The officinal preparations of lead are the semi-vitrified oxide, 

 the red oxide or minium, the white oxide or sub-carbonate, and the 

 acetate and sub-acetate. 



Oxides of Lead. 



Semi-vitrified Oxide of Lead, or Litharge. Plumbi 

 oxidum semi-vitreum, L.E.U.— This is a protoxide of lead in the 

 form of semi-transparent scales, of a reddish-yellow colour. It is 

 usually obtained during the calcination of lead, when separating 

 the silver with which the metal is often combined. The lead is 

 placed in a wind furnace, on a large dish, or cupel, exposed to a 

 strong heat, with a current of air from a large pair of bellows 

 directed upon its surface. It is used only in some pharmaceutical 

 preparations, particularly for forming, when boiled with oil, a 

 plaster, {Emp. plumbi, Ph.) which has been long known under the 

 name of Diachylon, and is used as a common application in exco- 

 riation of the skin, as a dressing to wounds, and for forming the 

 basis of other compound plasters. 



Red Oxide of Lead. Oxidum plumbi rubrum, Ph. E. 



Minium, the deutoxide of lead, or red lead, is obtained by exposing 

 the yellow oxide to heat and atmospheric air in a reverberatory 

 furnace, until it acquires a bright red colour. It is in the form of 

 a very heavy scaly powder, its specific gravity being 8-94. It is 

 sometimes applied to the same purposes as litharge, and is used in 

 considerable quantities as a flux. 



Subcarbonate of Lead. Plumbi subcarbonas, Ph. L.— -This 

 preparation, well known by the name of Cerusse, or white lead, 

 is prepared by suspending thin sheets of lead in the vapours of 



