the deposition of binoxide of manganese, and a green solution of manganate of potash passes through.

The solid permanganate of potash forms hard prismatic crystals which appear almost black, but are really dark red with a green reflection, and are at once known by the intense purple color which they impart even to cold water.

Manganate of Potash, KMnO4, is met with as a fine green solution which becomes red (permanganate) when diluted with much water, depositing brown hydrated peroxide of manganese. Dilute nitric acid produces a similar change.

56. Several other substances beside phosphate of lime might also be precipitated here, but this being far more common than any of the others, would be found in most cases to compose the precipitate. Phosphate of Alumina (112), Phosphate of Magnesia, Oxalate of Lime, and Fluoride of Calcium are some other common substances which might be met with here. (Phosphate of Baryta and Phosphate of Strontia would also be precipitated, but they are very uncommon.)

In order to be quite sure that phosphate of lime is present, the original solution should be mixed with some acetate of ammonia (prepared by adding acetic acid to ammonia until it reddens blue litmus paper) and divided into two parts.

One part is tested with oxalate of ammonia, which will produce a white precipitate of oxalate of lime.

The other part is tested with a drop of perchloride of iron, which will give a white precipitate of phosphate of iron.

The common form of phosphate of lime, Ca,2PO,, is Bone Ash, which is usually sold as a white powder, insoluble in water but dissolving easily in hydrochloric acid, with slight effervescence, due to the escape of carbonic acid from the carbonate of lime always present in bones, and often leaving a slight dark residue of charcoal.

Superphosphate of Lime, CaH2PO,, is commonly sold as a gray damp powder, which dissolves to a great extent in water yielding a strongly acid solution.

57. Phosphate of Magnesia would be known by its not yielding any precipitate on the addition of oxalate of ammonia, as above directed for the detection of lime; but if an excess of ammonia be afterwards added, and the solution briskly stirred (6) a crystalline precipitate of ammonio-phosphate of magnesia will be deposited.

Should there be no precipitate, add some phosphate of soda, and again stir. If this produces a precipitate, it will indicate that magnesia has been precipitated in the wrong place, in consequence of too little chloride of ammonium having been added in Table A.

The only common form of phosphate of magnesia is that of ammonio-phosphate or triple phosphate found in calculi, MgNH,PO; it is insoluble in water, but dissolves easily in hydrochloric acid.

58. Oxalate of Lime, CaC,O,, would be precipitated on mixing its original solution with acetate of ammonia, since it is insoluble in the acetic acid thus set free.

Oxalate of lime may be easily identified by its not effervescing when moistened with hydrochloric acid, unless it has been previously heated on a piece of glass or porcelain, when it becomes converted into carbonate of lime, which should be allowed to cool and tested with hydrochloric acid. It may also be tested for oxalic acid according to (114).

59. Fluoride of Calcium, CaF2, or Fluor Spar is met with in greenish or purple cubical crystals. Its powder resembles powdered glass in appearance and feel. It is not affected by water, and is dissolved only to a slight extent by diluted hydrochloric acid, the filtered solution yielding a flocculent precipitate with ammonia.

When heated on a knife, or thrown upon a hot surface, fluor spar generally crackles and flies off, at the same time emitting a peculiar phosphorescent light, somewhat resembling that of burning sulphur. It may be tested for fluorine according to Table G.

59a. If chromium be present in the form of chromate or

bichromate of potash, it will not be detected in the Table, but may be recognized by the yellow or red color of the solution, and by the yellow precipitates which it gives with acetate of lead and with nitrate of baryta.

60. The green solution produced by excess of potash will deposit a green precipitate of oxide of chromium when boiled. To confirm the presence of chromium, fuse a very little of the original substance with nitrate of potash, in a small tube (17), when a bright yellow mass of chromate of potash will be produced. This may be dissolved in water, and tested with acetate of lead which gives a yellow precipitate.

61. Metallic chromium, Cr, is not likely to be met with in ordinary analysis.

Oxide of Chromium, Cr,O,, is a green powder which is insoluble in water, but generally dissolves, at least partly, in hydrochloric acid, yielding a green solution. If it has been heated to redness, it is insoluble in hydrochloric and in nitric acids, but may be dissolved by boiling it with strong nitric acid, and adding a little chlorate of potash, which oxidizes the chromium into chromic acid, recognizable by the yellow precipitate of chromate of lead which is obtained on adding acetate of ammonia (56) and acetate of lead.

Chrome Iron Ore, FeCr,O,, is a hard mineral, of a dark

CHROMIUM COMPOUNDS.

67

brown or dark green color, which is almost insoluble in acids, and may be treated in a similar manner to the preceding, in order to detect the chromium.

Chromate of Potash, K,CrO4, forms bright yellow crystals easily soluble in water, giving a yellow solution, which becomes orange red when mixed with hydrochloric acid, from the production of bichromate of potash. Hydrosulphuric acid added in large excess to the acidified solution converts it into green chloride of chromium, rendering it opaque from the separation of sulphur.

Bichromate of Potash, K,CrO.CrO,, is sold in large irregular crystals of a fine orange red color, easily soluble in The solution of this salt also becomes green when mixed with hydrochloric and excess of hydrosulphuric acids.

water.

Chromate of Lead has been described at page 29.

Chrome Alum, KCr2SO,.12Aq., forms a dark purple crystals, which dissolve in water, yielding a purple solution, becoming green when boiled.

62. Examples for Practice in Table D.-The following substances may be analyzed (10):—

Chrome alum
Sulphate of nickel
Iron pyrites

Sulphate of manganese
Sulphide of iron

Oxide of zinc

Binoxide of manganese

Common alum
Sulphate of iron

Peroxide of iron
Sulphate of zinc
Bone-ash

Metallic zinc.