Carbonate of barytes is unalterable in the air, and at a red-heat. Upon heating it to redness, together with charcoal, caustic barytes is formed, whilst carbonic oxide gas escapes.

c. Fluoride of silicium and barium exists in small, hard, and colorless crystals; more frequently still, as a crystalline powder. It dissolves in 3800 parts of cold, but more readily in hot water. (Experiment No. 14.) The presence of free hydrochloric acid increases its solubility considerably. (Experiment No. 15.) It is unalterable in the air, and at 212°; when heated to redness, it is decomposed into fluosilicic gas, which escapes, and fluoride of barium which remains behind.

Strontia is determined either as SULPHATE OF STRONTIA, or

AS CARBONATE OF STRONTIA.

a. Sulphate of strontia, artificially prepared, is a white powder. It dissolves in 6895 parts of cold, and 9638 parts of

boiling water. (Experiment No. 16.) It is less soluble in water containing sulphuric acid, requiring as much as 11000 or 12000 parts. (Experiment No. 17.) It dissolves in solution of common salt, but is precipitated again by sulphuric acid. It is nearly altogether insoluble in alcohol as well as in spirits of wine. It does not alter vegetable colors; and is unalterable in the air, and at a red-heat. When exposed to a very intense redheat, it fuses without undergoing decomposition. When heated to redness, together with charcoal, access of air being precluded, it is transformed into sulphuret of strontium.

b. Carbonate of strontia, artificially produced, is a white delicate loose powder. It dissolves at the common temperature in 18045 parts of water. (Experiment No. 18.) The presence of ammonia diminishes its solubility. (Experiment No. 19.) It dissolves readily in solutions of sal-ammoniac and nitrate of ammonia, but is precipitated again from these solutions by ammonia. Water impregnated with carbonic acid dissolves it as a bi-carbonate. Its re-action is very feebly alkaline. It remains unaltered. in the air, and even at a red-heat; but when exposed to a very intense red-heat, it fuses, and gradually loses its carbonic acid. Upon heating it to intense redness together with charcoal, caustic strontia is formed, whilst carbonic oxide gas escapes.

§ 47.

3. LIME.

Lime is determined either as SULPHATE OF LIME or as CARBONATE OF LIME; for the latter purpose, it is precipitated first as

OXALATE OF LIME.

a. Anhydrous sulphate of lime, artificially produced, is a loose white powder. It dissolves at the common temperature in 430 parts, and at 212° in 460 parts of water. The presence of sal ammoniac, sulphate of soda, and common salt increases its solubility. The aqueous solution of gypsum does not alter vegetable colors. Sulphate of lime is nearly altogether insoluble in alcohol, as well as in spirits of wine. Exposed to the air, it slowly absorbs water; it remains unaltered at a dull red-heat. When heated to a bright redness, it fuses without undergoing decomposition. Upon being heated to redness together with charcoal, access of air being precluded, it is reduced to sulphuret of calcium.

b. Carbonate of lime, artificially prepared, is a white fine powder. It dissolves in 10601 parts of cold, (Experiment No. 20,) and in 8834 parts of boiling water, (Experiment No. 21). Its solution has a hardly perceptible alkaline reaction. Water impregnated with ammonia and carbonate of ammonia dissolves it far more sparingly, one part requiring about 65000 parts for its solution. (Experiment No. 22.) This solution is not precipitated by oxalate of ammonia. It dissolves more readily in solutions of sal ammoniac and nitrate of ammonia, but is preci

Neutral potass

Water impreg

pitated again from these solutions by ammonia. and soda salts likewise increase its solubility. nated with carbonic acid dissolves carbonate of lime as a bicarbonate. Carbonate of lime is unalterable in the air at 212°, and even at a red-heat; but upon the application of a more intense heat, it gradually loses its carbonic acid, more especially with free access of air. Attempts at calcining carbonate of lime completely, in a platinum crucible over a spirit-lamp, with double draught, have, however, failed. (Experiment No. 23.) It yields up its carbonic acid, (as carbonic oxide gas,) far more readily when heated to redness together with charcoal.

c. Oxalate of lime is a fine white powder, nearly absolutely insoluble in water. The presence of free oxalic acid and acetic acid increases its solubility slightly; but ammoniacal salts exercise no influence whatever in this respect. The stronger acids (hydrochloric acid, nitric acid) dissolve oxalate of lime readily; and from these solutions it is precipitated again unaltered by alkalies; and likewise (provided the excess of acid be not too great) by the addition in excess of alkaline oxalates, or of alkaline acetates. It is unalterable in the air, and at 212°; dried at 212°, its composition is as follows:-(Experiment No. 24.)

At a temperature of from 356° to 392°, oxalate of lime loses its water without undergoing decomposition; when heated to incipient dull redness it is decomposed, without actual separation of carbon, into carbonic oxide, which escapes, and carbonate of lime, which remains behind. The powder, which was previously of snowy whiteness, transiently assumes a grey color in the course of this process, even though the oxalate be of the most perfect purity. Upon the continued application of heat this grey color disappears again. If the oxalate of lime is heated in small coherent fragments, such as are obtained upon drying the precipitated salt upon the filter, the commencement and progress of the decomposition can be readily marked by this transient appearance of grey. If the process of heating be conducted properly and cautiously, the residue will not contain a trace of caustic lime.

§ 48.

4. MAGNESIA.

Magnesia is determined either as SULPHATE OF MAGNESIA, PYROPHOSPHATE OF MAGNESIA, OR AS PURE MAGNESIA. To transform it into the pyrophosphate, it is precipitated as BASIC

PHOSPHATE OF AMMONIA AND MAGNESIA.

a. Anhydrous sulphate of magnesia is a white opaque mass. It dissolves readily in water. It is nearly altogether insoluble in absolute alcohol; and but very sparingly soluble in spirits of wine. It does not alter vegetable colors. Exposed to the air, it absorbs water rapidly. It does not undergo decomposition at a moderate red-heat, but it is partially decomposed when heated to very intense redness. It loses part of its acid in this process of decomposition, and is afterwards no longer completely soluble in water. (Experiment No. 25.)