PART III.

Alkalies and Neutral Salts.

611

and in this state it is soluble in its own weight of water at 60°;but in the granular form, four parts of cold water are requiredfor its solution. When long kept in solution, its acid is de-composed, and its alkali remains in the state of a subcarbon-ate.' Alcohol also dissolves it readily. R is partially decom-posed by the weaker acids and the acidulous salts, and alsoby tamarinds and other sub-acid fruits, which reduce it to thestate of supertartrate; and it is completely decomposed bylime-water, muriate of barytes, magnesia, nitrate of silver, andacetate and superacetate of lead. Its constituents, abstractingthe water of crystallization, are, in 100 parts, 58-69 of acid,and 41-31 of alkali. 1

Medical properties and uses. — Tartrate of potass is a valu-able purgative, operating easily and without griping ; and evencorrecting the griping properties of some other substances, asof senna and the resinous purgatives, with which it is, there-fore, usually combined. The dose is from jj. to %]. in solution.

AQUA SUPERCARBONAT1S H3TA6SJE, Edin.Water of Supercarbonate of Potass.

" Take of water, ten pounds •, pure subcarbonate of potass,one ounce ; dissolve, and expose the solution to a current ofcarbonic acid gas arising from carbonate of Vime in powder,three ounces,- sulphuric acid, three ounces; and water, threejwtinds ; gradually and cautiously mixed. The chemical appa-ratus of Dr. Ncoih is well adapted for this preparation. Butif a larger quantity of the solution be required, an apparatuswhich will admit of a sufficiently great pressure should be em-ployed. The solution must be preserved in well-stopped vessels.

This water is seldom sufficiently impregnated with the acid,when made on a small scale ; but in the great way, and with anapparatus from which a much greater pressure is obtained, asolution is prepared for sale, which contains a very large quan-tity of uncombined carbonic acid.

Qitalitics. —When properly prepared, this solution has apungent, acidulous taste, and reddens tincture of litmus; isperfectly transparent, sparkles when poured into a glass, andeffervesces violently with all the acids.

Medical properties andUses. — This solution is tonic, diuretic,and antacid. It has also been regarded as a lithontriptic, andis much used in calculous cases: but its properties as a solventof calculi, if it possess any, must depend upon the potass itcontains, and, hence, the more completely it is impregnatedwith carbonic acid, the more its lithontriptic powers must be di-minished. There is, however, reason for believing, that evenpure potass when taken into the stomach exerts no influence

1 Murray's Chemistry, 2d ed. iv. 329.

R R 2

* Berzelius,