CARBONATE OF POTASH.

301

sure to the air it attracts water, and becomes liquid, forming the oleumtartari per deliquium. It is insoluble in alcohol, but is very soluble inwater; and in the Pharmacopoeia is an officinal solution, called liquorpotasses carbonatis, composed of twenty ounces of the salt dissolved ina pint of distilled water. The solution is colourless, inodorous, and has asp. gr. of 1’473.

Pure carbonate of potash may be prepared by the combustion of bitar-trate of potash and nitre (forming what is called white flux), lixiviating,concentrating by evaporation, and crystallizing. The primary form of thecrystal is a rhombic octahedron.

Characteristics. —It is known to be a carbonate by its effervescingwith the strong acids, and by a solution of it causing a white precipitate(soluble in acetic acid) with lime w r ater or with chloride of barium. Thatit is a potash salt is determined by the tests for potash already mentioned.From the bicarbonate of potash it is distinguished by its causing a brick-red precipitate with a solution of bichloride of mercury, the precipitatebeing percarbonate of mercury. Sulphate of magnesia produces a whiteprecipitate with the carbonate of potash, and not with the bicarbonate.This test, however, w r ill not recognise the carbonate when mixed witha large quantity of bicarbonate.

Composition. —Mr. Phillips ( Pharmacopoeia ) says, one hundred partsof the carbonate of potash of the shops loses about 16 parts of waterwhen heated to redness. Hence supposing the carbonate to have beenpure (which that of commerce never is) its composition would be asfollow's :—

Eq. Eq.Wt. PerCent.

Potash. 1 .... 48 .... 57*6

Carbonic Acid ......... 1 .... 22 .... 26*4

Water.1*. . ♦ . 13-5 .... 16*0

Pure Granulated Carb. Potash . 1 . . . . 83'5 .... 100*0

The pure crystallized salt contains two equivalents of water of crystal-lization, and its equivalent weight, therefore, is 88.

Impurities. —The ordinary impurities in this salt are silicic acid, thechlorides, and sulphates. The first is detected by supersaturating withhydrochloric acid, evaporating, and igniting the residue : the silicic acidis' insoluble in water. The other impurities are detected by supersatu-rating the salt with nitric acid: if the resulting solution give a whiteprecipitate with nitrate of silver, the presence ofhchloride is to be infer-red : if it produce a white precipitate with chloride of barium, a sulphateis present.

Physiological Effects. —Its effects are in quality precisely those ofcaustic potash already described, but their intensity is much less, onaccount of the presence of carbonic acid, which diminishes the alkalineproperties of the base. When it is taken into the stomach in large quan-tities, it acts as a powerfully caustic poison, sometimes inducing deathin twelve hours, and producing symptoms similar to those caused by themineral acids: at other times, however, the patient recovers from the im-mediate effect of the alkali, but in consequence of the altered condition ofthe alimentary canal the assimilative process cannot be carried on; andafter dragging on a miserable existence for a few weeks, the unfortunatesufferer dies of absolute starvation. And lastly, in some cases, the causticoperation of the poison is principally confined to the oesophagus, causingstricture and death. In one case, related by Sir Charles Bell ( Surgical