Sulphate of potassium is employed in the production of carbonate by a process analogous to the Le Blanc soda process, and enters into the manufacture of certain kinds of glass and alum. It is also used to a considerable extent as a manure.
Bisulphate of Potassium. (Fe., Bisulfate de Potasse ; GER., Znifaoh Schwefelsaures Kali.) For mula, salt when pure crystallizes in flattened rhombic prisms, soluble in twice their weight of water at 15°, and less than half that amount at 100°. The solution has a strung acid reaction and taste. The crystals fuse at 197°, and at about 600° lose half their sulphuric acid.
Bisulphate of potassium is usually prepared by heating the neutral sulphate with sulphuric acid, in the proportions of about 87 parts of the salt with 49 parts of acid. It is necessary, how ever, as a rule, to have the acid in excess. It is also prepared largely as a bye-product in the decomposition of nitre by sulphuric acid—in the preparation of nitric acid, &c. It is used for cleansing metals, as a chemical reagent, and in calico printing and dyeing. For the latter purposes, it is only used for lower styles of work, as a substitute for tartaric acid. Its application requires care, as the fibre of the cloth is apt to be damaged by freed sulphuric acid.
Tartrate of Potassium.—The nentral salt is of slight importance. It crystallizes in right rhombic prisms, which are permanent in the air and have a strong saline taste. Tartrate of potassium is obtained by neutralizing cream of tartar with chalk or potassium carbonate. It is very soluble in water.
The bitartrate, or acid tartrate (Fe., Tartrate wide de Potasse ; GER., Saures Weinsaures Kali, or Weinstein), is a substance of very considerable importance. It is commonly known as cream of tartar, or, in the crude state, " argol," and exists in the juice of the grape, tamarind, pine apple, and many other fruits (see Argol). It forms small, hard, colourless, prismatic crystals of irregular grouping, with a strong acid taste and reaction, especially in solution. Exposed to heat iu a close vessel it is decomposed with evolution of inflammable gas, leaving a mixture of finely divided charcoal and potassium carbonate. This residue has already been mentioned when speaking of the preparation of potassium carbonate. It is known as " black flux."
To refine the crude article and produce the commercial cream of tartar, the argol is dissolved in hot water and crystallized, the operation being repeated until a pure product is obtained. It is usual to employ a little pipeclay and animal charcoal or albumen to remove the colouring matter.
Cream of tartar and the crude tartar are both largely used in the manufacture of tartaric acid. The finer qualities form esteemed reagents in dyeing and priutiag operations, though, on the score of expense, their use is not as groat as in former times. As a mild substitute for tartaric acid, cream of tartar forms a discharge on dipped blues and turkey reds, and is used in steam colours for blues and greens. In conjunction with alum and the salts of tin, it is employed to some small extent in mordanting, but it is in all these processes a very mild agent. It acts probably in two ways ; (1), as a corrective of bad, hard waters, with regard both to lime and iron ; (2), as a mild acidifying agent, enabling the fibre, especially woollen stuffs, to take the colour well. For inferior work, sulphuric and arsenic acids, and bisulphate of potash, have to a great extent superseded tartaric acid and cream of tartar, but where economy is not of the first importance, the finer sorts of bitartrate hold their own as a safe reagent.
Rochelle salt is a tartrate of potassium and sodium, forming large clear prismatic orystals, with a mild saline taste. They effloresce slightly in the air and dissolve in 1 parts of water. The usual method of preparation is to saturate a hot solution of cream of tartar with carbonate of soda and evaporate to a thin syrup, from which the salt erystallizes out. It enters into certain medicinal preparations, forming a well-known purgative. J. L.
term is applied scientifically only to the oxides of the metal sodium, but practically it covers several other sodium compounds, more particularly the hydrate and carbonates. Three oxides are known, the euboxide, monoxide, and dioxide. Of the suboxide little is known. The monoxide and dioxide are both formed when metallic sodium is heated in dry air or oxygen gas. The former may be prepared pure by heating sodium hydrate with sodium ; thus :— NaHO Na = + H.