i The common brass cocks is an alloy of these two metals. The union is, how ever, so partial, that on heating the cock the lead melts out and leaves the copper. This process is called liquation. The nitrate of lead is made by heating the me tal with warm nitric aeid,—a crude and weak solution of this salt of lead, consti tuted the disinfecting liquid of Ledoyen & Calvert, which has been so preposter ously overrated. It is capable of decom posing animal sulphurets, phosphurets, and hence of removing the unpleasant smells of drains and water-closets, but beyond this action it has hardly any, and it is quite incapable of breaking up and rendering innocuous a miasin in the way in which chlorine does. Calvert fell a victim to his trials of this solution in the Fever Hospitals in Canada.
Lead constituted the writing-table of the ancient Greeks and Romans.
When metallic lead is strongly heated in the reverberatory furnace it beomes of a dull color on the surface, loses its me tallic appearance, and puts on the appear ance of a dross or powder. When this dross is healed to a low ignition, it be comes of a dull yellow color, and is called common massicot ; and, by a higher heat and longer exposure to the fur, it as sumes a deeper yellow, and is then called massicot. This is the protoxide of lead, and consists, in 112 parts, of 104 lead and 8 oxygen. When it contains about four per cent. of carbonic acid, it is called li tharge. It unites with acids, and is the base of all the salts of lead. If the pro toxide, or metallic lead, be subjected, during 48 hours, to the heat of a rever beratory furnace, it passes to the condi tion of red oxide, or what is commonly called mininm, or red lead. Its composi tion is, in 116 parts, 104 lead, 12 oxygen. Lead forms a compound with chlorine. The union is effected by adding muriatic acid, or a solution of common ialt, to the acetate or nitrate of lead dissolved in wa ter. This chloride fuses at a temperature below redness, and forms, as it cools, a semi-transparent horny mass, sometimes called horn lead.
The pigment called mineral, or patent yellow, is a compound of the chloride and protoxide of lead. It is prepared for the purposes of the arts by the action of moistened sea-salt on by which means a portion of the protoxide is con verted into chloride.
Wurrx-LEAD, or carbonate of lead, is prepared by exposing narrow slips, or thin lead, to the steam of vinegar, in a close vessel. The slips are laid on bars of wire above the surface of the boiling vinegar. For flake-white, dilute sulphu ric acid is preferred. i There is, (says Thomson,) only one direct poison among the salts of lead, which is the carbonate ; and, when the other salts of lead display poisonous ef fects, these are to be attributed either wholly, or in part, to their conversion into the carbonate. This salt acts as a powerful sedative astringent on the liv ing system, diminishing the nervous en ergy, and, consequently, greatly depress ing the powers of the cirfulation, and lowering the tone of the muscular system. It is probably taken into the blood, which may account for its slow operation when it is introduced into the stomach in mi nute doses, for a considerable length of time, and also for its producing similar effects, when applied to the surface of the body denuded of the cuticle, or in a state of ulceration.
Great mischief has been produced by the use of lead in dairies. If the milk runs into the slightest acidity, some lead will be dissolved, and injurious conse quences will follow if it is taken into the stomach.
Lead in Wines is detected by a black precipitate, which will be instantly pro duced by the following mixture :—Ex pose equal parts of sulphur and powder ed oyster-shells to a white heat for a quarter of an hour. cold, add an equal quantity of cream of tartar, and boil them with water in a strong bottle for an hour. Transfer to ounce phials, and add to each 20 drops of muriatic acid.
To reduce Red Lead. Heat in a Hessian crucible 2 oz. of red lead with 2 drs. of powdered charcoal, and 1 oz. of common salt. The result will be 2 oz. of pure me tal.
When nitrate of lead or of bismuth is boiled with carbonate of lime, magnesia, or barytes, these salts are decomposed, and the oxides are so completely precipi tated that hydrosulphuret of ammonia shows no traces of them in the solution. Carbonate of lime, when added to a cold solution of these metals, precipitates only the oxide of bismuth. Several methods have been proposed for separating the lead which is contained in the bismuth of commerce; but carbonate of lime is pre ferable.