Lead bichromate

Lead Bichromate. See Lead Dichromate in Vol 3 of Encycl, C284-R... 

Lead chromates are prepared by precipitation techniques from soluble salts ia aqueous media. The raw material Hst iacludes a number of different lead compounds, eg, Htharge, lead nitrate, basic lead acetate, basic lead carbonate, as well as acids, alkahes, sodium bichromate, and sodium chromate. The typical reaction can be represented by the foUowiag equation ... 

If-Phenylenediamine, when warmed with dilute sulphuric acid and potassium bichromate or lead peroxide, gives the odour of quinone (p.-iqa). After warming and cooling, extract with ether. The ethereal solution has a yellow colour. Decant the ether extract on to a watch-glass and leave it to evapoiate in the air. A deposit of microscopic yellow crystals remains. See Appendix., p. 286. 

Chrom-gehaltf m. chromium content, -gelatine, /. chromatized gelatin, bichromated gelatin, -gelb, n. chrome yellow (lead chromate) Cologne yellow (lead chromate and... 

The largest solubility isotope effects are found for sparingly soluble salts. For example, lead chloride and potassium bichromate are 36% and 33.5% more soluble in H20 than D20 at 298.15 and 278.15 K, respectively. For the more soluble salts, NaCl and KC1, the values are 6.4% and 9.0%. Interestingly LiF and LiCl.aq have inverse effects of 13% and 2%, respectively. Recall that lithium salts are commonly designated as structure makers . Almost all other electrolytes are structure breakers . 

Amm acetate soln and add sufficient Na bichromate soln to ppt all lead as chromate. Test for the completion of destruction by transferring a portion of slurry to a filter paper and treating the filtrate with a few drops of Na bichromate soln. Confirm the absence of LA by washing.with distd w,the residue on filter,free of so azide salts, drying it,and subjecting a 20 mg portion to the impact test, using 2 kg wt. The material should not detonate... 

Chromate and bichromate of lead—known respectively as lemon and orange chrome, or as chrome yellow and chrome red—yellow ochre, gamboge, and other pigments, furnish a yellow hue. 

Bichromate of Lead—2 PbO, CrOj— chrome red— may bo obtained by boiling oxide of lead, or its car-bonato, with on aqueous solution of monochromate of potassa, or by digesting the neutral chromate of lead in a dilute solution of caustic potassa. Liebig prepared it by adding a neutral ebromate to fased nitre, and washing the residuum it is an insoluble, scarlet colored powder. 

Lead chromates and lead molybdates are produced by precipitation of soluble salts in aqueous media. Various lead sources include litharge, lead nitrate, basic lead actetate, and lead carbonate. The lead carbonate and basic lead acetate are used primarily to control particle size. Other ingredients include acids, alkalis, sodium bichromate, and sodium chromate. Additionally, molybdate orange manufacture involves the use of sodium molybdate and sodium sulfate as raw materials. 

In a large lead-lined vessel, 300 grams of sublimed, still moist, anthracene (calculated on the basis of 100 per cent product) is stirred with 6 liters of water and 600 grams of sodium bichromate. The mixture is heated to 80°C. over a Fletcher burner, and 1800 grams of 50 per cent sulfuric acid is added over a period of 10 hours. Chromic-acid should always be present, and the mixture should be stirred with a wooden or glass rod. Finally, the mixture is boiled for 2 hours, replacing the water lost by evaporation. The precipitate is then filtered off and washed thoroughly. The mother liquor can be worked up to recover chrome alum or chromic sulfate. 

Potassium Cyanate.—When iso-cyanic acid is neutralized with potassium hydroxide, potassium cyanate is obtained. Potassium cyanate is also obtained when potassitun cyanide is oxidized by means of lead oxide or potassium bichromate. 

For the manufacture of alizarin on a large scale a very pure anthraquinone is required, and this is generally prepared by oxidation of anthracene with sodium bichromate and dilute sulphuric acid. The anthracene is generally a 50-per-cent, product which has oeen converted into a soft powder by subliming with superheated steam. The oxidation takes place in lead-lined vessels in which the mixture is heated by direct steam. By employing a pure anthracene and a not too concentrated oxidation-mixture, the anthraquinone separates as soft grey powder, which is freed from acid by washing wdth water. The crude product is then dried, dissolved in concentrated sulphuric acid, and precipitated with water. A further purification is effected by sublimation with superheated steam. 

The manveine dyestuffs are formed, although only in small quantities, by oxidation of primary monamines in neutral solution with potassium bichromate, cupric chloride, lead peroxide, and other oxidising agents. It has not been determined with certainty what monamines are capable of yielding dyestuffs of this class but it is probable that the manveine C27H2iN4 is formed from three molecules of toluidine (ortho and para ) and one molecule of aniline, according to the equation —... 

These salts are yellow, orange, or red, the latter colour predominating when the acid is in excess, except in the case of dichromate of lead, which is red. The soluble chromates are recognised by their colour, which is changed to green when alcohol and hydrochloric acid are added, and the mixture is boiled. The general formula for neutral chromates is MO, Cr O3 and for bichromates, MO, 2 Cr O3. 

Bichromate of lead, 2 Pb 0 -H Cr 0, is found native, as the red-lead ore, forming beautiful red crystals. It may also be formed by fusing the neutral chromate of lead with nitrate of potash, or by boiling carbonate of lead with chromate of potash and is much used as a paint. 

Chromate of lead, PbO, CrOs, is an insoluble powder, of a very fine yellow colour, much used in painting, under the name of chrome yellow. It is formed by the action of soluble salts of lead on chromate, or bichromate of potash. 

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