Lead Bromide, PbBr2, is obtained by treating a soluble lead salt with solution of potassium bromide. In many respects it resembles the chloride.

Lead Iodide, Pbl. Plumbi Iodidum, U. S. P.

Preparation. I part of lead nitrate in 20 parts of water is poured, with constant stirring, into I part of potassium iodide in 10 parts of water :

The resulting precipitate is collected on a filter, washed well with cold water, and carefully dried. Instead of the lead nitrate, one may use 9 parts of lead acetate in 90 parts of water acidified with a little acetic acid, and 8 parts of potassium iodide in 80 of water.

Properties.-Lead iodide is a heavy, lemon-yellow powder, without odor or taste; soluble in about 2000 parts of water at 15° and in 200 parts of boiling water, "separating from the latter solution in brilliant, golden-yellow spangles or crystalline laminæ. Very slightly soluble in alcohol, but soluble, without color, in solutions of the fixed alkalies, in concentrated solutions of the acetates of the alkalies, of potassium iodide, and of sodium hyposulphite, and in a hot solution of ammonium chloride. When moderately heated, the salt fuses to a thick, reddish-brown liquid, which congeals, on cooling, to a yellow, crystalline mass. higher temperature it is decomposed, with the evolution of violet vapors of iodine, leaving a lemon-yellow residue of lead oxyiodide."

At a

Uses. The principal use of lead iodide is in medicine, where it is employed externally in the form of an ointment.

Lead Fluoride, PbF2, is precipitated as a white insoluble powder when hydrofluoric acid is added to a soluble salt of lead.

OXYGEN SALTS OF LEAD.

Lead Sulphate, PbSO4, is found in nature as lead vitriol or anglesite, in transparent rhombic crystals. These crystals are isomorphous with those of strontium and barium sulphate.

Lead sulphate is prepared by precipitating lead nitrate or acetate with sodium sulphate. It is only slightly soluble in water and in dilute acids, but somewhat more soluble in concentrated sulphuric acid. Hot concentrated nitric acid dissolves it, and it is readily soluble in solutions of sodium thiosulphate or ammonium acetate.

Lead sulphate is a by-product in the manufacture of aluminum acetate in calico print-works and dyeing establishments. It is used to mix with

other lead compounds in the manufacture of paint and in the manufacture of lead chromate.

Lead Nitrate, Pb(NO3). Plumbi Nitras, U. S. P.

Preparation. This salt is prepared by adding, in small portions at a time, 10 parts of lead oxide to 23 parts of nitric acid (25 per cent.), previously mixed with an equal weight of water and warmed:

The solution is filtered, and, after the addition of a few drops of nitric acid, is set aside to crystallize.

Properties. Lead nitrate crystallizes in large, anhydrous, regular, mostly octohedral crystals, isomorphous with the nitrates of barium and strontium. When these crystals separate from hot solutions they are white and opaque, but if formed by the spontaneous evaporation of cold solutions they are transparent. The salt is soluble in 2 parts of water and in 0.75 part of boiling water; almost insoluble in alcohol. On the application of heat nitrous fumes are evolved and a residue of lead oxide remains.

Uses. Lead nitrate is used extensively in the manufacture of mordants for use in dyeing and calico-printing, and in the manufacture of lead chromate.

Lead Nitrite, Pb(NO2)2, is obtained by decomposing silver nitrite with lead chloride. The solution is concentrated in a vacuum, when yellow, prismatic crystals separate, which are readily soluble in water.

Lead Phosphate, Pb3(PO4)2, forms as a white precipitate when solutions of lead acetate and sodium phosphate are mixed. When phosphoric acid is added to a boiling lead nitrate solution, lustrous, white crystals having the composition PbHPO4 separate.

Lead Borates.-A number of these salts appear to exist, one of which is obtained by precipitating a soluble lead salt with solution of borax. It appears to have the composition Pb,BO11.4H2O.

Lead Silicates.-These compounds are formed in the manufacture of some kinds of glass. When equal weights of lead oxide and silica are fused together a yellow glass is formed.

Lead Carbonate, PbCO,.-The normal lead carbonate is found in nature as the mineral cerussite, or it may be artificially prepared by precipitating a solution of lead acetate with one of ammonium carbonate. This compound is not much used.

Basic Lead Carbonate, (PbCO),Pb(OH) ̧. Plumbi Carbonas, U. S. P. White Lead. This compound was known to the ancients.

Preparation.-White lead is manufactured on a large scale by the following processes:

1. The Dutch Process is the oldest, and is employed in Holland, Belgium, and some parts of Germany. It consists in placing coils or buckles of lead in earthenware pots, in the bottom. of which is a small quantity of vinegar. The lead is placed on projections in the pots so as not to come in direct contact with the liquid; the walls of the pots are perforated just above the vinegar, so as to allow a free circulation of air and gas. A number of the pots are placed together as shown in Fig. 84, and FIG. 84.

after covering each with a wooden plate they are surrounded with horse manure or spent tan-bark. The fermentation of the manure or tan causes the requisite elevation of temperature to vaporize some of the acetic acid of the vinegar, which acts on the lead with the formation of basic lead acetate. This is slowly converted into carbonate by the carbon dioxide which results from the fermentation. After some weeks the lead will be found wholly converted into basic carbonate.

2. In the English Method sheet-lead is melted on the hearth of a reverberatory furnace so as to convert it into oxide, and this in turn is intimately mixed with a small quantity of solution of lead acetate. The resulting mass is placed in a series of closed troughs communicating with one another, and so arranged as to admit the passage of a current of carbon dioxide. This gas is obtained by the combustion of coke in a furnace provided with a blast to give impulse to the gas.

3. The German or Austrian Method involves the action of acetic acid and carbon dioxide on sheets of lead as in the Dutch process, but a large number of the lead coils are placed in a room with vinegar and tan on the floor. The tan is caused to ferment and furnish the necessary carbon dioxide.

4. The French Method consists in dissolving an excess of lead or lead oxide in acetic acid, so as to form basic lead acetate, and then passing carbon dioxide into this solution, by which means two molecules of lead oxide are converted into basic carbonate, while neutral acetate of lead remains. This is again converted into basic acetate, which is, in turn, decomposed by more carbon dioxide.

The principle involved in this method was first explained by Thénard, but it is generally known as the Clichy Process, because of the works

located at Clichy, near Paris. Fig. 85 shows a plan of these works. In the tub A, the litharge is dissolved in acetic acid, the solution being aided

by means of the stirrer e e. The solution of basic lead acetate is run into the vessel E, where the impurities subside, and the clear solution is then run into the decomposing vessel FF, which is supplied with several hundred tubes for the admission of the carbon dioxide. In 12 to 16 hours the conversion is complete. The neutral lead acetate is run into the tank m and returned to A, while the semi-liquid basic lead carbonate is drawn into the tank o.

The carbon dioxide is generated in D and purified in the vessel j.

Many more processes have been patented and worked in a small way in the production of white lead, but it is probable that in this country, as well as in most foreign countries, the Dutch method is given the preference.

The product in all the foregoing processes is finely ground with water, well washed to remove lead acetate, and finally dried.

Some white lead is made from lead sulphate by heating together this salt and solution of sodium hydrate, whereby a basic lead sulphate is formed, and this, by boiling with sodium carbonate solution, is converted into basic lead carbonate and sodium sulphate.

Properties.-Basic lead carbonat is a heavy, white,

amorphous powder. It is without odor or taste, and is perma

nent in the air.

Water and the other ordinary solvents do not

dissolve it, but acetic acid and dilute nitric acid readily dissolve it with effervescence. When heated to 200° it turns yellow without charring, and gives off its carbon dioxide, leaving a residue of oxide.

Uses. White lead is frequently mixed with gypsum, and with barium sulphate or heavy spar. Hamburg white is a mixture of 1 part white lead and 2 parts barium sulphate. Dutch white contains 3 parts of the barium sulphate to I part of white lead. The amount of barium or calcium salt is readily determined by treating the powder with warm acetic or dilute nitric acid, which will dissolve only the lead salt. Lead sulphate is sometimes used as an adulterant. The chief objection to it is its deficient covering power when made into paint.

Paint is chiefly made by grinding white lead with oil, and then thinning with linseed oil or oil of turpentine, according to the use to which it is to be applied.

LEAD AND SULPHUR.

Lead Sulphide, PbS, is very widely distributed in nature as a strongly lustrous, bluish-gray mineral. It may be artificially prepared by passing hydrogen sulphide into a solution of lead acetate. It is a black, insoluble powder, which is scarcely dissolved by hydrochloric acid, but converted by hot concentrated nitric acid into lead sulphate. At a red heat it melts, and it may be sublimed in a current of carbon dioxide or hydrogen. Lead sulphide is used in the glazing of certain kinds of pottery-ware.

TITANIUM.

Atomic Weight, 48.

Valence, IV.

Symbol, Ti. Occurrence.-Titanium occurs as oxide, TiO2, under the names of rutile, anatase, and brookite, and in titanates such as CaTiO, and FeTiOg. Preparation and Properties.-The metal is a gray, metallic powder, and has been obtained by heating the double fluoride, K,TiF。, with potassium. It burns when heated in the air, and is dissolved by dilute hydrochloric and sulphuric acid with evolution of hydrogen.

COMPOUNDS OF TITANIUM.

Titanium Chloride, TiCl, and Titanium Fluoride, TiF4, are known. The latter forms compounds like K„TiF, analogous to the silico-fluoride of potassium, KaSiFe

Titanic Acid, H4TiO4, is obtained as a white, amorphous powder on adding ammonium hydrate to the hydrochloric acid solution of the titanates. It readily loses i molecule of H2O, and becomes TiO(OH)2, analogous to CO(OH)2.

Titanium Dioxide, TiO2, is abundantly found in nature. It is almost insoluble in the acids, being dissolved only by hydrofluoric acid. It forms titanates on fusion with the alkalies.