47*

Alkalies and Neutral Salts.

part ni.

1220 to 1000. If the salt be not very pure, repeat the solutionand crystallization."

Barilla, besides the subcarbonate of soda, contains sulphateand muriate of soda, charcoal, lime, magnesia, argil and silex,from which these processes are intended to separate it. Theearths being insoluble are separated by the solution and filtra-tion ; while the foreign salts remain dissolved in the residuaryliquor after the subcarbonate of soda has crystallized. In theLondon formula, it has been justly observed', the evaporationis directed to be tob soon stopped. One pound of barillayields, when properly managed, from 3iij to gv of the crystallizedsubcarbonate.

A pure subcarbonate of soda is now manufactured, on agreat scale, by the decomposition of sulphate of soda, and ofmuriate of soda, which will probably supersede altogether theprocesses ordered in the pharmacopoeias.*

Qualities. — Subcarbonate of soda has a mild alkalescenttaste, and changes the vegetable blue and red colours to green.Its crystals are large transparent octohedrons, truncated at thesummits of the pyramids, which effloresce when exposed to adry air, and crumble down into a white opaque powder. Itundergoes the watery fusion, at 150° Fah.; is soluble in twoparts of water at 60°, and in considerably less than its weightof boiling water, its abundant water of crystallization assistingthe solution of the salt at that temperature. Its constituents,according to the late analysis of D'Arcet 3 , are, in TOO parts,16'0* of acid, 20"85 of alkali, and 63 , 61 of water; but, Berardmakes them to be 13'98 of acid, 23'33 of alkali, and 62'69 ofwater. By treating this salt in the method described undersubcarbonate of potash, any muriates or sulphates it may con-tain are detected, while the tartaric acid, added to its solution,discovers potash, by forming a precipitate of the supertartrate.

Medical properties and uses. — This salt is antacid and deob-struent. It is less acrid than the subcarbonate of potash; andhence is in more general use in dyspepsia and acidities of thestomach, and in scrophulous affections. Its use has been latelystrenuously recommended in hooping-cough, the protractionof which it is said to prevent. It is given at first, after thestomach and bowels have been duly evacuated, in combinationwith ipecacuanha and opium, and afterwards, when the violenceof the cough has abated, with myrrh or cinchona. 4 The doseof this salt is from grs. x, to 5j, given twice or thrice a day.

i London Medical Review, April 1808. 139.

* For experimental purposes, it is obtained, Mill purer from the crystallised acetate byignition.

3 Annates de Chimie, lxxi. 208. 4 Mtdieo~Chirurgical Transactions, vol. i.