Several hydrated forms of the oxide are known, and a colloidal variety may be obtained by the dialysis of a strong hydrochloric acid solution of sodium molybdate.
Molybdenum trisulphide, MoS3, is obtained by saturating a solution of an alkaline molybdate with sulphuretted hydrogen and adding a mineral acid.
Ann., 1826, 8, p. 23), by converting lead molybdate into lead nitrate, obtained the value 95.
Of other lead minerals we may mention the basic sulphate lanarkite, PbO PbSO 4; leadhillite, PbSO 4.3PbCO 3; the basic chlorides matlockite, PbO PbC12j and mendipite, PbC1 2.2PbO; the chloro-phosphate pyromorphite, PbC12.3Pb3(P04)2, the chloro-arsenate mimetesite, PbC12.3Pb3(As04)2; the molybdate wulfenite, PbMoO 4; the chromate crocoite or crocoisite, PbCrO 4; the tungstate stolzite, PbW04.
Other precipitants of phosphoric acid or its salts in solution are: ammonium molybdate in nitric acid, which gives on heating a canary-yellow precipitate of ammonium phosphomolybdate, 12[M00 3] (NH 4) 3 PO 4, insoluble in acids but readily soluble in ammonia; magnesium chloride, ammonium chloride and ammonia, which give on standing in a warm place a white crystalline precipitate of magnesium ammonium phosphate, Mg(NH 4)PO 4.6H 2 0, which is soluble in acids but highly insoluble in ammonia solutions, and on heating to redness gives magnesium pyrophosphate, Mg 2 P 2 0 7; uranic nitrate and ferric chloride, which give a yellowish-white precipitate, soluble in hydrochloric acid and ammonia, but insoluble in acetic acid; mercurous nitrate which gives a white precipitate, soluble in nitric acid, and bismuth nitrate which gives a white precipitate, insoluble in nitric acid.
There are several volumetric methods for assaying lead ores, but the best known is that based on the precipitation of lead by ammonium molybdate in an acetic acid solution.
A standardized solution of ammonium molybdate is then added from a burette.
As long as the solution contains lead, the addition of the molybdate solution causes a precipitation of white lead molybdate.
The appearance of a yellow colour shows that all the lead has been precipitated and that the solution contains an excess of molybdate.
The molybdate solution should be of such a strength that i cc. will precipitate o oi gramme of lead.
The salts of arsenic acid, termed arsenates, are isomorphous with the phosphates, and in general character and reactions resemble the phosphates very closely; thus both series of salts give similar precipitates with "magnesia mixture" and with ammonium molybdate solution, but they can be distinguished by their behaviour with silver nitrate solution, arsenates giving a reddish-brown precipitate,whilst phosphates give a yellow precipitate.
The phosphorus in solution reacts with the molybdate ion to produce a blue coloration whose intensity is directly proportional to the concentration of phosphorus.
These data were collected on a solution of sodium molybdate.
Chem., 1848, 44, P. 301), or by long fusion of a mixture of ammonium molybdate, potassium carbonate, and boron trioxide (W.
Chem., 18 94, 5, p. 280), by heating pure sodium molybdate in hydrochloric acid and estimating the amount of sodium chloride formed, obtained the value 96.087.
The ordinary ammonium molybdate, used as a test reagent for phosphates, is a salt of composition (NH4)10M012041; it has been examined physicochemically by J.
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