Oils which contain sulphur-compounds are subjected to a special process of refining in which cupric oxide or litharge is employed as a desulphurizing agent.
Many substances were employed in ancient medicine: galena was the basis of a valuable Egyptian cosmetic and drug; the arsenic sulphides, realgar and orpiment, litharge, alum, saltpetre, iron rust were also used.
In regard to the ancients' knowledge of lead compounds, we may state that the substance described by Dioscorides as, uoXv,3Saiva was undoubtedly litharge, that Pliny uses the word minium in its present sense of red lead, ana that white lead was well known to Geber in the 8th century.
The temperature is then raised, and the scum which forms on the surface is withdrawn until pure litharge forms, which only takes place after all the tin, arsenic and antimony have been eliminated.
Formerly all argentiferous lead had to be cupelled, and the resulting litharge then reduced to metallic lead.
After it has been melted down and brought to a red heat, the blast, admitted at the back, oxidizes the lead and drives the litharge formed towards the front, where it is run off.
The working door through which the litharge is run off lies under the flue which carries off the products of combustion and the lead fumes, the lead is charged and the blast is admitted near the fire-bridge.
The zinc and some lead are oxidized; part of the zinc passes off with the fumes, part is dissolved by the litharge, forming a melted mixture which is skimmed off and reduced in a blast-furnace or a reverberatory smelting furnace.
The liquid litharge when allowed to cool solidifies into a hard stone-like mass, which, however, when left to itself, soon crumbles up into a heap of resplendent dark yellow scales known as "flake litharge."
"Buff" or "levi gated litharge" is prepared by grinding the larger pieces under water.
Litharge is much used for the preparation of lead salts, for the manufacture of oil varnishes, of certain cements, and of lead plaster, and for other purposes.
The Kassner process for the manufacture of oxygen depends upon the formation of calcium plumbate, Ca2Pb04, by heating a mixture of lime and litharge in a current of air, decomposing this substance into calcium carbonate and lead dioxide by heating in a current of carbon dioxide, and then decomposing these compounds with the evolution of carbon dioxide and oxygen by raising the temperature.
Another process depends upon the formation of lead chloride by grinding together litharge with salt and water, and then treating the alkaline fluid with carbon dioxide until it is neutral.
It may be artificially prepared by leading sulphur vapour over lead, by fusing litharge with sulphur, or, as a black precipitate, by passing sulphuretted hydrogen into a solution of a lead salt.
By fusing litharge with boron trioxide, glasses of a composition varying with the proportions of the mixture are obtained; some of these are used in the manufacture of glass.
Lead silicates are obtained as glasses by fusing litharge with silica; they play a considerable part in the manufacture of the lead glasses.
Fischer, Ber., 1884, 17, p. 102); by passing the vapours of orthoaminodiphenylmethane over heated litharge (0.
Sometimes reagents are placed in the combustion tube, for example lead oxide (litharge), which takes up bromine and sulphur.
The conversion of silver into the sulphide may be effected by heating with antimony sulphide, litharge and sulphur, pyrites, or with sulphur alone.
The sulphur and litharge, or Pfannenschmied, process was used to concentrate the gold in an alloy in order to make it amenable to " quartation," or parting with nitric acid.
Litharge and red lead are used in silver and gold assays, acting as solvents for silica and any metallic oxides present.
For use with wood which is exposed to moisture, as in the case of wooden cisterns, a mixture may be made of 4 parts of linseed oil boiled with litharge, and 8 parts of melted glue; other strong cements for the same purpose are prepared by softening gelatine in cold water and dissolving it by heat in linseed oil, or by mixing glue with one-fourth of its weight of turpentine, or with a little bichromate of potash.
On the 1st of November 1772 he deposited with the Academy a sealed note which stated that sulphur and phosphorus when burnt increased in weight because they absorbed "air," while the metallic lead formed from litharge by reduction with charcoal weighed less than the original litharge because it had lost "air."
The oil, when boiled with small proportions of litharge and minium, undergoes the process of resinification in the air with greatly increased rapidity.
Then by slow degrees a proportion of " dryers " is added - usually equal weights of litharge and minium being used to the extent of 3% of the charge of oil; and with these a small proportion of umber is generally thrown in.
It combines directly with sulphur and phosphorus, and is readily oxidized when heated with metallic oxides (such as litharge, mercuric oxide, manganese dioxide, &c.).
Antimony trioxide occurs as the minerals valentinite and senarmontite, and can be artificially prepared by burning antimony in air; by heating the metal in steam to a bright red heat; by oxidizing melted antimony with litharge; by decomposing antimony trichloride with an aqueous solution of sodium carbonate, or by the action of dilute nitric acid on the metal.
When the lead melts and begins to oxidize, the lead oxide, or so-called litharge, combines with or dissolves the non-metallic and readily oxidizable constituents of the ore, while the gold and silver alloy with the lead.
The door of the muffle is then opened and the current of air which is drawn over the scorifier rapidly oxidizes the lead, while the melted litharge gradually closes over the metal.
Other metals, except the silver and gold, also oxidize, and are carried by the melted litharge into the cupel.