Lead oxide

“ When the nitrate is heated, either lead oxide is obtained or else the oxide in combination with peroxide.
Lead chloride, PbCl2, is precipitated from the soluble salts of lead when a strong solution is treated with hydrochloric acid or a metallic chloride. It is soluble in considerable quantities in hot water, and therefore if the solutions be dilute or hot, the precipitation of lead chloride does not occur, and if a hot solution be cooled, the salt separates in brilliant prismatic crystals. It fuses when heated (like silver chloride) , but is insoluble in ammonia. ”

“ Red lead is produced by raising massicot, which is the commercial name for oxide of lead, to a high temperature, short of fusion, during which it absorbs oxygen from the air and is converted into red lead or minium, also an oxide of lead. The color is lasting, and is unaffected by light when it is pure and used alone, but any preparation containing lead or acids mixed with it deprives it of color, and impure air makes it black. ”

“ In the same way with lead driers, excessive amounts of lead oxide seem to have no beneficial effects on the drying of an oil, and when the percentage which seems to be the most beneficial, namely 0.5% lead oxide, is exceeded, the film is apt to become brittle. ”

“ The muffle is placed in a furnace, where it is strongly heated. Under the action of the air entering the muffle the copper of the silver alloy is oxidised, but as the oxide of copper is infusible, or, more strictly speaking, difficultly fusible, a certain quantity of lead is added to the alloy; the lead is also oxidised by the air at the high temperature of the muffle, and gives the very fusible lead oxide. The copper oxide then fuses with the lead oxide, and is absorbed by the cupel, whilst the silver remains as a bright white globule. ”

“ In this last case an alkaline solution of lead oxide is formed, and the tin acts on the solution in such a way as to reduce the lead to the metallic state, and itself passes into solution. It is very remarkable that lead displaces tin when in combination with acids, whilst tin, on the contrary, displaces lead from its alkali compounds. By dissolving the mass obtained in water, and adding alcohol, sodium stannate is precipitated, which may then be dissolved in water and purified by re-crystallisation. ”

“ The hardening is based on the reaction of the lead oxide with glycerine (Moraffsky) .
[50] It is very instructive to observe that lead not only easily forms basic salts, but also salts containing several acid groups. Thus, for example, lead carbonate occurs in nature and forms compounds with lead chloride and sulphate. The first compound, known as corneous lead, phosgenite, has the composition PbCO3,PbCl2; it occurs in nature in bright cubical crystals, and is prepared artificially by simply boiling lead chloride with lead carbonate. ”

“ It is, however, useful in internal decoration, as it retains its colour well, even when subjected to the action of gases. Red lead is a lead oxide. It is used chiefly in the priming coat and as a base for some red paints. Like white lead, it is injured if exposed to acids or impure air, which cause discoloration and decay. Oxide of iron is used chiefly as a base in paints used for covering iron-work, the theory being that no destructive galvanic action can be set up, as might be the case with lead paint when used on iron. ”

“ Many methods are employed. Sometimes the lead sulphide is decomposed by heating it with cast iron. The iron takes up the sulphur from the lead and forms [135] easily-fusible iron sulphide, which does not mix with the heavier reduced lead. But another process is more frequently used: the lead ore (it must be clean; that is, free from earthy matter, which may be easily removed by washing) is heated in a reverberatory furnace to a moderate temperature with a free access of air. During this operation part of the lead sulphide oxidises and forms lead sulphate, PbSO4, and lead oxide. ”

“ A stick of green wood is forced into it, and the vapours and gases set free expose new surfaces to the air, which at this temperature has only a mildly oxidizing effect. The pole, the use of which is awkward, has been replaced by dry stream, which has a similar effect. To remove tin, arsenic and antimony, the lead has to be brought up to a bright-red heat, when the air has a strongly oxidizing effect. Tin is removed mainly as a powdery mixture of stannate of lead and lead oxide, arsenic and antimony as a slagged mixture of arsenate and antimonate of lead and lead oxide. ”

“ On ignition, it loses oxygen and forms litharge. Commercial red lead is frequently contaminated with this oxide, which may, however, be removed by repeated digestion with lead acetate. Its common adulterants are iron oxides, powdered barytes and brick dust. Acids decompose it into lead dioxide and monoxide, and the latter may or may not dissolve to form a salt; red lead may, therefore, be regarded as lead orthoplumbate, Pb2PbO4. It is chiefly used as a pigment and in the manufacture of flint glass. ”

“ Prepare a 10 per cent. solution for use.
Lead Nitrate (Pb (NO3) 2) can be purchased pure. It is used for standardising.
Lead Dioxide (PbO2) occurs as a dark-brown powder. It is used as an oxidizing agent and for absorbing sulphurous oxide. It can be prepared by digesting red lead with warm dilute nitric acid; washing and drying the residue.
"Litharge," PbO.—It can be purchased as a yellow heavy powder. It is used in dry assaying as a flux, as a desulphurising agent, and also as a source of lead. It always contains some silver, the amount of which must be determined. ”

“ By digesting red oxide of lead in dilute nitric acid; or by infusing a mixture of protoxide of lead and chlorate of potassium at a heat a little below redness, and washing the powdered mass in water; or by transmitting a current of chlorine gas through a solution of neutral acetate of lead. This oxide gives up half its oxygen at a red heat; acids also decompose it. Its chief use is in chemical analysis, to separate sulphurous acid from certain gaseous mixtures, which it converts into sulphuric acid, which it at the same time absorbs, forming sulphate of lead. ”

“ Although, of course, if the cupel is very coarse-grained the metal may sink into the hollows.
Copper, antimony, tin, and most other metals, form powdery oxides, which are not of themselves easily fusible, and it is necessary when these are present to add some solvent or flux to render the oxide sufficiently fluid. Fortunately, oxide of lead is sufficient for the purpose; hence, mixed oxides of copper and lead, provided the lead is present in proper proportion, form a fluid slag. ”

“ Taking oxide of lead therefore as the illustration, I conceive that it is not the particles of oxygen and lead which polarize separately under the act of induction, but the molecules of oxide of lead which exhibit this effect, all the elements of one particle of the resulting body, being held together as parts of one conducting individual by the bonds of chemical affinity; which is but another term for electrical force (918.) .
1702. In bodies which are electrolytes we have still further reason for believing in such a state of things. Thus when water, chloride of tin, iodide of lead, &c. ”

“ It has been observed at all times, that the oxide of lead carries off with it, into the cupel, a little silver in the state of an oxide. This effect becomes less, or even disappears, when there is some copper remaining; and the more copper, the less chance there is of any silver being lost. The loss of silver increases, on the other hand, with the dose of lead. Hence the reason why it is so important to proportion the lead with a precision which, at first sight, would appear to be superfluous. ”

“ Oxide of Lead, in the form of red lead or litharge, is a valuable flux; it easily dissolves those metallic oxides which are either infusible or difficultly fusible of themselves, such as oxides of iron or copper. The resulting slag is strongly basic and very corrosive; no crucible will long withstand the attack of a fused mixture of oxides of lead and copper. With silicates, also, it forms very fusible double silicates; but in the absence of silicates and borates it has no action upon lime or magnesia. ”

“ Oxide of lead, called “litharge,” enters into the composition of flint glass, and in combination with a larger quantity of oxygen forms “red lead,” a substance much used in painting. Lead is found in many parts of England, especially Cornwall, where many lead mines exist; it is got from the sulphuret called “galena,” which is lead in union with sulphur. What is called “black-lead” is not lead at all, but is an ore of iron, being iron in combination with carbon. Lead is about eleven-and-a-half times heavier than water. ”

“ When carbonic acid is present the dissolved oxide is soon precipitated as basic carbonate, so that the corrosion of the lead becomes continuous. Since all soluble lead compounds are strong cumulative poisons, danger is involved in using lead cisterns or pipes in the distribution of pure waters. The word “pure” is emphasized because experience shows that the presence in a water of even small proportions of calcium bicarbonate or sulphate prevents its action on lead. All impurities do not act in a similar way. Ammonium nitrate and nitrite, for instance, intensify the action of a water on lead. ”

“ Red oxide of lead turns black when heated in the glass tube closed at one end, and liberates oxygen, which is easily detected by the introduction of an ignited splinter, when a more lively combustion of the wood proves the presence of uncombined oxygen. The red oxide in this case is reduced to the protoxide. Heated upon platinum foil, it first turns black, is reduced to the protoxide, and melts into a dark yellow liquid. In the reduction flame, upon charcoal, it is reduced to the metal with intumescence. ”

“ While he also prevents interruption of the operation by means of water-jackets, he uses hot-blast, and produces, besides metallic lead, large volumes of lead fumes which are drawn off by fans through long cooling tubes, and then forced through suspended bags which filter off the dust, called “blue powder.” Thus, a mixture of lead sulphate (45%) and oxide (44%) with some sulphide (8%) , zinc and carbonaceous matter, is agglomerated by a heap-roast and then smelted in a slag-eye furnace with grey slag from the ore-hearth. ”

“ Yes; it may be beaten out into a pretty thin leaf, but it will not bear drawing into fine wire. It is not only very fusible, but very readily oxidized by heat, changing into a powder, or a scaly matter, which may be made to take all colours by the fire, from yellow to deep red. You have seen red lead?
Geo. Yes.
Tut. That is oxide of lead exposed for a considerable time to a strong flame. Lead may even be changed into glass by a moderate heat; and there is a good deal of it in our finest glass.
Geo. What is white lead?
Tut. It is lead corroded by the steam of vinegar. ”

“ When metallic sulphides are present in the ore, an excess of oxide of lead helps to keep the sulphur out of the button of metal. In addition to the oxide of lead required as a flux, some will be required to provide the lead in which the silver is to be collected. Oxide of lead, mixed with charcoal or flour, yields, when heated, a multitude of minute buttons of metal uniformly distributed through the mass of the charge ”

“ It has already been stated that when red lead is exposed to heat, oxygen gas is given out, and it may be added, a small trace of water; and yellow oxide remains. [Pg 44]
This experiment requires considerable skill. If too great a heat is used, a part of the lead is reduced or revived as it is termed; if too little heat, then a part of the red lead remains unaltered. In performing this experiment I use a small clean iron spoon to hold the red lead, and cover it by another iron spoon ”

“ If solutions of the salts of lead, thallium, silver, bismuth, nickel, and cobalt are decomposed by the current between platinum electrodes, metal is deposited at the negative, and oxide at the positive electrode. Manganese is precipitated only as peroxide. The formation of peroxide is, of course, effected by the ozone found in the electrolytic oxygen at the positive pole; the oxide existing in solution is brought to a higher degree of oxidation, and is separated out. ”

“ The lead ore is not charged in large quantity and left for an indefinite time, but is thrown in in quantities of a few shovelfuls at a time, the object being to effect extremely rapid volatilisation and consequent oxidation. The proportion of ore to fuel is 1 ton to 1 ton, and the result is said to be the conversion of 95 per cent. of the charge into its equivalent in white lead. In the first or wide chamber, the coke is oxidised, carbonic oxide being the resulting gas, the rapid volatilisation of the galena or sulphide of lead also taking place in the same chamber. ”

“ Lead which contains a good deal of pewter or tin must be rejected, because it tends to produce elongated drops or tails.
From two to three tons are usually melted at once in the large establishments. The surface of the lead gets covered with a crust of oxide of a white spongy nature, sometimes called cream by the workmen, which is of use to coat over the bottom of the cullender, because without such a bed the heavy melted lead would run too rapidly through the holes for the granulating process, and would form oblong spheroids. ”