(Experiment No. 4 b) It dissolves completely in caustic potass; the color of this solution is yellow. It is unalterable in the air, and at 212°. Upon being exposed to an intense red heat, that portion of the chlorine which is combined with the potassium escapes completely, and metallic platinum and chloride of potassium remain; but there still remains some chloride of platinum and potassium undecomposed, even after the mass has been kept in fusion for a long time. Complete decomposition takes place, however, if the salt is heated to redness in a stream of hydrogen gas.

Soda is usually weighed as SULPHATE OF SODA, NITRATE OF SODA, CHLORIDE OF SODIUM, OR CARBONATE OF SODA.

a. Anhydrous neutral sulphate of soda occurs as a white powder, or a white, very friable, mass. It dissolves readily in water; in absolute alcohol it is sparingly soluble, but somewhat more readily in spirits of wine; (Experiment No. 5;) the presence of free sulphuric acid increases its solubility in absolute alcohol. It is neutral to vegetable colors; exposed to a moist atmosphere, it slowly attracts water. (Experiment No. 6.) It remains unaltered at a gentle heat, but when exposed to an intense red heat, it fuses without decomposition or diminution of weight.

The acid sulphate of soda (bisulphate of soda).

3

(Na O, S 0, +H O, SO3) is uniformly produced when a solution of the neutral salt impregnated with sulphuric acid in excess is evaporated to crystallization; this acid salt fuses even at a gentle heat; it may be readily converted into the neutral salt in the same manner as the bisulphate of potass is reconverted into the neutral sulphate (vide § 42 a).

b. Nitrate of soda crystallizes in obtuse rhomboidal cubes. In analysis it is mostly obtained as an amorphous mass. It dissolves readily in water, but is nearly altogether insoluble in absolute alcohol, and but little more soluble in spirits of wine. It is neutral to vegetable colors, and unalterable in the common atmosphere; but when exposed to a very moist air, it absorbs water. It fuses without decomposition at a temperature far below red heat; at a higher temperature it undergoes the same decomposition as nitrate of potass. (Vide § 42 b.) (Comp. Experiment No. 7.)

(Experiment No. 8.) Crystals

c. Chloride of sodium crystallizes in cubes, octahedrons, and hollow square pyramids. In analysis it is frequently obtained as an amorphous mass. It dissolves readily in water; it is hardly soluble in absolute alcohol, and but sparingly so in spirits of wine. It is neutral to vegetable colors. Exposed to a somewhat moist atmosphere, it slowly absorbs water. of this salt that have not been kept long drying decrepitate when heated, yielding a little water, which they hold confined between their plates. At a red heat, it fuses without decomposition; at a white heat, and in open vessels, even at a bright red heat, it volatilizes in white vapors. (Experiments No. 9.)

d. Anhydrous carbonate of soda exists as a white powder, or a white, very friable mass. It dissolves readily in water, but is insoluble in alcohol. Its reaction is strongly alkaline. Exposed to the air, it absorbs water very slowly. At a strong red-heat it fuses without decomposition, and without volatilizing.

Ammonia is most advantageously weighed as CHLoride of am

MONIUM, AND CHLORIDE OF PLATINUM AND AMMONIUM. Under certain circumstances, ammonia may likewise be determined from the volume of nitrogen separated from it.

a. Chloride of ammonium crystallizes in cubes and octahedrons, but more frequently in feathery crystals. In analysis we obtain it uniformly as a soft white mass. It dissolves readily in water, but is difficultly soluble in spirits of wine. It does not alter vegetable colors, and is persistent in the air. Solution of sal-ammoniac when evaporated in the water-bath, loses a small proportion of ammonia, and becomes slightly acid. The diminution of weight occasioned by this loss of ammonia is very trifling. (Experiment No. 10.) At 212° sal ammoniac loses nothing, or next to nothing, of its weight. At a higher temperature it volatilizes readily, and without undergoing decomposition.

b. Chloride of platinum and ammonium occcur either as a heavy lemon-yellow powder, or in small, hard, octahedral crystals of a bright yellow color. It is difficultly soluble in cold, but more readily in hot water. It requires for its solution 26535 parts of absolute alcohol; 1406 parts of spirits of wine of 76 per cent., 665 parts of spirits of wine of 55 per cent. The presence of free acid sensibly increases its solubility. (Experiment No. 11.) It is unalterable in the air, and at 212°. When heated to redness, chlorine and chloride of ammonium escape, and metallic platinum remains behind as a spongy mass.

c. Nitrogen gas is colourless, tasteless, and inodorous, miscible with air without producing the slightest coloration; it is indifferent to vegetable colors; its specific gravity is 0.9706. (Air=1). One litre (one cubic decimeter) weighs at 32. and 0.76 metres atmospheric pressure (29.8 of the barometer) 1.2609 grammes.

It is difficultly soluble in water; one volume of gas requiring, at 64.4° 24 volumes of water.

BASES OF THE SECOND GROUP.

$ 45.

1. BARYTES.

Barytes is generally weighed as SULPHATE OF BARYTES, CARBONATE OF BARYTES, FLUORIDE OF SILICIUM AND BARIUM.

a. Sulphate of barytes, artificially produced, is a fine white powder. It is almost absolutely insoluble in cold as well as in hot water; the presence of free acid hardly increases its solubility. It is quite unalterable in the air, at 212°, and even at a red heat. When heated to redness, together with charcoal, it is transformed into sulphuret of barium. This reduction, however, takes place only if the access of air is precluded.

b. Carbonate of barytes, artificially produced, is a white powder. It dissolves in 14137 parts of cold, and in 15421 parts of boiling water, (experiment No. 12); it dissolves far more readily in solution of chloride of ammonium, or nitrate of ammonia. From these solutions it is, however, precipitated again by caustic ammonia. Water containing free carbonic acid dissolves carbonate of barytes as a bi-carbonate. It is almost absolutely insoluble in water impregnated with ammonia and carbonate of ammonia, one part requiring about 141000 parts. (Experiment No. 13.)

Solution of carbonate of barytes has a feebly alkaline reaction.