SODA SALTS.

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Chlorate of Potash.

Chlorate of potash, KO.ClOs, is prepared by passing chlorine into a hotconcentrated potash lye, and is separated by cooling the fluid, in which it isnot very readily soluble. By heating chlorate of potash the oxygen is setfree, and chloride of potassium remains. In dyeing it is used as an ageingmaterial, especially in conjunction with steam, and in several methods to bedescribed in the course of the work. Its chief impurities are chloride ofpotassium and nitrate of potash.

Hypochlorite of Potash.

Of this salt we shall speak more fully under the head of Chlorimetry. Itsformula is K0,C10 ; it is a yellow-tinted fluid with a peculiar odour. Thechief application is as a bleaching agent. It may be prepared by passingchlorine into a dilute and cold solution of potash until the alkaline reactionceases.

SODA SALTS.

Carbonate of Soda.

Carbonate of soda, or, simply, soda, Na0,C0 3 , occurs in commerce as anartificial product, and partly as the result of the calcination of plants. It isalso found native in the waters of certain lakes and in sea water. The plantsfrom which soda-ash is prepared grow, and in many instances are speciallycultivated, near the sea shore. The genera chiefly employed, in addition tothe species of Fucus thrown up by the sea itself, are those known as Salsola,Atriplex, Salicornia, &c. The process of burning is of a most primitive kind,and is conducted in pits dug in the sand of the sea shore. The heat of com-bustion is generally very intense, and the ash appears as a hard, semi-fusedmass, termed in the trade crude soda or soda-ash, or sal-soda. The best variety,termed Barilla soda , is that obtained from Alicante, Malaga, Carthagena, theCanary Islands, and contains on an average 25 to 30 per cent of carbonateof soda. The next place as regards value is held by Blanquette soda importedfrom Aigues-Mortes, while an inferior variety in common use is the Varecsoda, calcined on the coasts of Normandy and Brittany from the Fucusvesiculosus.

The artificial preparation of soda-ash may be considered as one of themost perfect processes of manufacturing chemistry; indeed, one might say themost perfect and complete process that could be devised. The importance ofthe invention of M. Leblanc is almost without parallel, especially when thereis added the improvement of the recovery of the sulphur from the soda-waste.The process consists of four stages, all of which we shall, as briefly as possible,describe under the following heads:—

1 . Sulphate of soda is prepared from salt by treatment with sulphuric acid,

or by roasting common salt with a native metallic sulphuret, such asiron pyrites.

2 . The sulphate is converted into crude soda by roasting with a mixture

of chalk and small coal.

3. The crude soda is refined by lixiviation and evaporation.

4- The obtaining of sulphur from the soda-waste.

i- Sulphate of soda is generally obtained by treating common salt withsulphuric acid, the hydrochloric acid gas being condensed in condensing- or

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