ness, and examined. It sometimes consists of, or contains titanic acid.

76. ILVAITE.*

The finely-powdered mineral is moistened with a suitable quantity of water, in a porcelain capsule, some concentrated hydrochloric acid and a little nitric acid added, and the whole heated to complete gelatinization. The mass is then evaporated to perfect dryness on a water-bath, during which operation it is frequently stirred.

The dry mass is moistened with concentrated hydrochloric acid, then dissolved in chlorine water, the silicic acid filtered off, and treated in the usual manner (No. 75).

From the solution, diluted with the washing-water, the sesquioxide of iron is precipitated by ammonia, the precipitate allowed to subside in a covered vessel, and rapidly filtered off; the solution should first be passed through the filter, which is kept covered, as far as possible, to prevent absorption of carbonic acid. The precipitate is washed by means of the wash-bottle arranged for the purpose, dried, ignited, and weighed as sesquioxide of iron.

The filtrate from the sesquioxide of iron is acidulated with hydrochloric acid, concentrated by evaporation, in a flask, mixed with ammonia, the lime precipitated by oxalate of ammonia, and treated as in No. 12.

The mineral contains about 1.5 per cent. of protoxide of manganese, and 0.5 per cent. of alumina, both of

*The compact variety from Elba is not rare. It may also be obtained artificially by fusing together 6 parts of forge-scales, 3 parts of fine white quartz-sand, and 1 parts of calcined marble, at a strong white heat.

which are contained in the precipitated sesquioxide of iron, and must be separated from it as in Nos. 21 and

25.

About 1.5 per cent. of water is also present as an unessential constituent; its quantity may be ascertained by ignition in a covered crucible.

In order to ascertain directly the relative amounts of protoxide and sesquioxide of iron, the process described in No. 24 must be followed.

77. CHRYSOLITE (OLIVINE).

2 (MgO, FeO), SiO2.

The very finely-powdered mineral is decomposed by digestion with concentrated hydrochloric acid, the mass dried upon the water-bath, moistened with concentrated hydrochloric acid, and, after some time, mixed with water and filtered from the separated silica.

Small amounts of copper and tin, which are contained in many specimens of olivine, are detected and separated by mixing the, solution with saturated sulphuretted hydrogen-water, until it smells strongly, and allowing it to stand for some time in a closed vessel.

The solution filtered from the precipitate is concentrated by evaporation, some chlorate of potassa being added to peroxidize the iron.

The sesquioxide of iron may be precipitated by an excess of ammonia, and the magnesia separated from it by boiling the solution until all the free ammonia is expelled, when the sesquioxide of iron remains, and may be filtered off.

This filtrate contains, besides magnesia, a small quantity of protoxide of manganese and protoxide of nickel,

which latter is wanting only in the olivine of meteoric iron. These are precipitated by sulphide of ammonium, an excess of which is, as far as possible, to be avoided. The precipitate is not to be filtered off until it has separated so as to leave the solution perfectly clear; it may then be washed with very dilute sulphide of ammonium. If both metals are present only in small quantities, the sulphide of manganese may then be separated from the sulphide of nickel by treating it, upon the filter, with very dilute hydrochloric acid, in which the sulphide of nickel is, practically, insoluble. The small quantity of sulphide of nickel is then ignited in the air, and weighed as protoxide. The manganese is precipitated from the solution by carbonate of soda, at a boiling heat.

The liquid filtered from the precipitate produced by sulphide of ammonium, is mixed with ammonia, and the magnesia precipitated by phosphate of soda (No. 6).

In the analysis of olivine, the iron, when converted into sesquioxide, may also be separated from the other bases by succinate of ammonia (No. 21).

78. DATOLITE.

(3 CaO, 3HO, BO,) SiO,

For the determination of water, a weighed quantity of the mineral is heated to bright redness.

If the unignited mineral, in a finely-powdered state, be digested with moderately strong hydrochloric acid, it becomes a gelatinous mass. If the mixture be heated to boiling, and filtered while hot, boracic acid separates from the solution in crystals.

The finely-powdered mineral is decomposed by digestion with hydrochloric acid, and the mass evaporated to dryness, when a great part of the boracic acid is

volatilized; after exposure for a considerable time to a temperature of 100°, the residue is heated with water containing hydrochloric acid, the silicic acid filtered off, washed, dried and ignited.

The filtrate is neutralized with ammonia, and the lime precipitated by oxalate of ammonia (No. 12).

By this process the boracic acid cannot be determined directly but only by difference, because a large part of it volatilizes during evaporation. In order to make a direct determination, the mineral is decomposed by hydrochloric acid, or a retort furnished with a receiver, distilled to dryness, and the distillate containing the boracic acid poured back upon the residue, with which it is digested for some time, and then filtered from the silicic acid. The lime is then precipitated by a large excess of oxalate of potassa, filtered, and the filtrate concentrated by evaporation. From this the boracic acid is precipitated as a double fluoride of boron and potassium. For this purpose it is placed in a platinum dish with a little potassa, then mixed with a small excess of hydrofluoric acid, and evaporated to dryness. For the separation of the other salts, the mass is treated with a moderately concentrated solution of acetate of potassa, allowed to stand for some time, and the double fluoride of boron and potassium thrown upon a weighed filter, and washed with the solution of the acetate. The acetate of potassa is then washed out with alcohol. The double fluoride is dried at 100° and weighed.

79. ULEXITE.

NaO, 2B00 ̧+2 (CaO, 2B003) +18HO.

3

After determination of the water the mineral is dissolved in hydrochloric acid, neutralized with ammonia,

and the lime precipitated by oxalate of ammonia. The filtered solution is concentrated by evaporation, and the boracic acid separated as in No. 78 as a double fluoride of boron and potassium.

For the determination of the soda another portion is dissolved, the lime precipitated by oxalate of ammonia, the filtrate evaporated to dryness, and heated to drive off the ammoniacal salts. The mass is then digested with strong hydrofluoric acid, evaporated to dryness, digested with concentrated sulphuric acid, and evaporated to drive off the fluoride of boron. The sulphate of soda is finally ignited, a piece of carbonate of ammonia being held in the crucible.

I. The very finely-powdered and levigated mineral, dried at about 200°, is very intimately mixed, in a capacious platinum crucible, with 4 or 5 parts of carbonate of baryta; the crucible is then inclosed in an earthen crucible, which is placed in a wind-furnace with a good draught, and exposed for at least half an hour to an intense white heat, so that the contents may be firmly aggregated into a cinder-like mass. decomposition takes place more rapidly, and with greater certainty, when the crucible is exposed to a blowpipe flame, so that the mass fuses completely.

The

Or the mineral is mixed, in a silver crucible, with 4 parts of hydrate of baryta, previously freed by heat from its water of crystallization, and the mixture heated to fusion.

The mass is then turned out of the crucible into a capacious dish, a quantity of water poured over it, and hydrochloric acid gradually added in slight excess,