HYDRATE OF POTASH,

415

c.

heat it fuses, and at a higher temperature is volatilized. It is odourless, but hasa caustic, urinous taste. It rapidly decomposes organic substances. It possessesthe properties of an alkali in an eminent degree.

Characlerlstics. —Potash, free or combined with an acid to form a neutral salt, isvecognised by the following characters:—The hydrosulphurets, ferrocyanides, andcarbonates, produce no precipitate with its Solutions. Tartaric (in excess,) perch-loric, and carbazotic acids, occasion precipitates of the bitartrate, Perchlorate, andcarbazotate of potash respectively. Chloride of plantinum throws down a yel-low precipitate. Lastly, the potash salts communicate a violet tinge to the flameof alcohol.

Free potash is distinguished from its salts by its communicating a green colourto the infusion of red cabbage or syrup of violets; by its reddening turmeric, andrestoring the blue colour of litmus reddened by an acid ; by its not whitening limewater, or effervescing on the addition of an acid; by its soapy feel; by its solubilityin alcohol; and by its dissolving alumina.

Impurities.— Potassa fusa of the shops contains various impurities, such as ses-quioxide of iron, carbonate of potash, and silica. These, however, do not mate-rially affect its medicinal value.

"ßoiling water ooinmonly leaves oxide of iron undissolved, which should not excecd 1*25per cent.: the Solution neutrallized with nitric acid gives a faint precipitate with a Solution ofnitrate of baryta, and raore with Solution of nitrate of silver,—owing to the presenee of impu-rities" Ph. Ed.

The nitrate of baryta detects sulphates, while nitrate of silver is a test for Chlo-rides.

Composition. —Pure anhydrous potash has the following composition:—

Potassium .Oxygen

Potash................ 1

Eq. Wt. Per Cent Bcrzeüus.

.. 40 ........ 8334 ........ 83-05

.. 8 ........ lfi-66 ........ 16-95

48 ........ 100-00

100-00

The hydrctle of potash is thus composed :-

Potash.Watet.

Atoms. 1 .. 1 .

Eq. Wt.

. 48 ..

Per Cent.. 84-2 . .. 15 8 ..

BerzeHus.

... 84... 16

Hydrate of Potash___ 1 ........ 57 ........ 100.0 ........ 100

Physiological Effects, a. On Vegetables. —Caustic potash promptly destroysthe parts of living plants with which it is placed in contact, and even in the dilutestate kills haricots [Phaseolus vulgaris) in a few hours. (Marcet, in De Candolle,Phfs. Feget.) -

ß. On animals generali}/. —It acts on animals generally as an energetic causticpoison. It is, says Orfila, (Toxicnl. Gener.) of all poisons, that which most fre-quently perforates the stomach. He found, that injected into the jugular vein ofa dog, it coagulated the blood, and caused speedy death. It is, however, remark-able, that when mixed with the blood out of the body, it not only does not coagu-late it, but actually prevents its spontaneous coagulätion. Magendie has observed,that by the exhibition of alkalis to dogs, the urine aequires alkaline properties.

y. On Man. —The general Operation of alkalis has been already noticed (see pp.194 and 207.) The local action of caustic potash, especially when in the solid form,is exceedingly energetic. It neutralizes any free acid in the part to which it is applied,and decomposes whatever ammoniacal salts may be present, causing the evolution ofammoniacal gas. It combines with fibrin and albumen, forming soluble Compounds{fibrate and albuminate of potash.) Hence, rubbed between the fingers, it corrodesand dissolves the epidermis, and thereby gives rise to a soapy feel. Gelatine is alsoreadily dissolved by it, and any phosphate of lime which may be present is de-posited. These phenömena are to a certain extent comparable to those of saponi-flcation. As, then, potash and the other alkalis form soluble Compounds with sub-stances which enter largely into the composition of the organized tissues we can