Compounds of Lead.- One of the most im portant lead compounds is plumbic carbonate (carbonate of lead, white lead), PbCO, - the cerussite of mineralogists, and now largely mined in the United States as an ore of lead. White lead is manufactured on a large scale, and is extensively used in the arts as a white pigment and as a body for other colors in paints. (See. PAINTS). Another leading com pound is plumbic chloride (chloride of lead), The minerals matlockite and mendipite are both oxychlorides of lead. A basic chloride of lead is made for use as a white pigment, which is, however, not so serviceable as ordi nary white lead. Lead acetate (sugar of lead), Pb(C11-1•01)2, 31-100, is prepared by dissolving massicot in dilute acetic acid. It can be ob tained in transparent crystals or in scales by evaporating the solution. It is soluble in one and one-half parts of cold water, and in eight parts of alcohol. Like litharge, it is in the manu facture of oil-varnishes. Minium or red lead is much used in the manufacture of flint glass, as a cement and as a pigment. For glass making it requires to be made of very pure lead as a slight trace of copper would impart a color to the glass. Minium is prepared. by heating massicot or monoxide of lead to a temperature of 600° F. in iron trays, in an oven, carefully avoiding fusion. More oxygen is thus gradually absorbed; and a bright-red compound 'is formed which is the red lead of commerce. Orange lead, made from white lead instead of from massicot, is a very pure kind of red lead. Yellow lead, so called some times by manufacturers, is a mixture of the oxides of lead and antimony, which is to some extent used to give a yellow color to earthen ware, and as a pigment. The so-called black lead (see GRAPHITE), of which pencils, etc., are made, contains no lead.
Lead in Medicine.— Most of the lead com pounds used in medical practice are made into external applications for 'disorders' of the sys tem which, manifest themselves upon the skin, although some are employed as sedatives, as tringents, etc. Lead acetate is an approved
internal remedy in typhoid fever, diarrhoea and other diseases. Of plasters, ointments and the like, lead carbonate, lead iodide and lead oleate are familiar constituents.
Lead Poisoning.— Under the influence of moist air, or of water in which air is held in suspension, the hydroxide of lead is formed, • and this is soluble in water. To this condition is to be attributed many cases of poisoning by drinking water which has been standing for some time in lead pipes or Vessels. The use of soluble salts of lead in the arts is a' frequent cause of painful• and sometimes poisoning, from the metal finding its into the system. The effects often are not immedi. ate as minute doses are apparently harmless, but these being oft repeated have a cumula tive effect and the seizure is sudden. The glazing of culinary vessels with lead; the color ing of confectionery with the chromate, chlo ride or carbonate of lead; the sweetening of sour wine by litharge or oxide of lead; the drinking of water which has passed through. new lead-pipes; and living much in newly painted with lead-colors, all these may cause exposure to this peril, and often produce lead or saturnine poisoning. But the most frequent and virulent cases occur among painters and persons engaged in white-lead fac tories. In lead-poisoning the countenance as sumes a sallow, earthy hue, the skin becomes dry and harsh, the digestion is deranged and the bowels constipated, and a sweetish metallic taste is felt in the mouth. A specially import ant sign is the appearance of a blue or violet line along the margin of the gums and teeth, due to the formation of sulphide of lead. There is sometimes kidney derangement, mus cular palsy, severe disturbance of the brain, and even epilepsy and some form of insanity. The . most commonly occurring result of lead-poison- , ing is lead-colic, or painters' colic. See ELECTROCHEMICAL INDUSTRIES; ORE DEPOSITS.