Salt is one of the component parts of animal, vegetable, and mineral bodies. It may be distinguished from other matters, such as earths, by its solubility in less than 200 times its weight of boiling water ; by affecting the organs of taste; and being capable of crystallization, either by itself, or in combination with several earths or alkalies.
Salts are divided into two principal classes, namely, acid and alka/ine : from the mutual combination of both, there is formed a third kind, known under the name of neutral salts.
I. Acid salts, possess a sour taste, and change the blue colour of vegetable pigments into red. They are divided, according to the three kingdoms of Nature, into vegetable, animal, and mineral ; but, having already given an outline of this distinction (vol. i. pp. 10, 11), we must refer the reader to the principal acid salts, under their alphabetical heads.
III. Nuetral Salts, are such as are from a combination of acids and alkalies. The principal and most useful of this class is, the Common or Seasalt. It differs from all other neutal substances of this nature, in its being purely saline, and oc-casioning thirst, after it has been swallowed. The primitive figure of its crystals is that of a cube; but, on evaporating a solution of salt, the smaller cubic particles assume the secondary form of hollow squares. When the crystals are perfectly pure, they are not affected by moist air; and, in this state, 100 parts contain, according to Bergman, 52 of muriatic acid, or spirit of salt; 42 of soda, or mineral alkali; and 6 of water of crystalization : though we believe, with Gren, that the proportion of the fluid part is greater, and that of the two first ingredients somewhat smaller. Nature furnishes us with this neutral salt, either in a solid state, in mines; or dissolved in the sea; or in saline springs.
If it be obtained from the bowels of the earth, it is called Rock-salt; and is generally very hard and transparent, though it is sometimes opaque, white, and sometimes of red, green, blue, or other shades. The purest of this kind is colourless; the other species are purified by solution in water, and by re-crystallization, before they can be employed for culinary purposes. The principal saL mines of Rock-salt are in, the vici-nity of Cracow, in Poland, and at Northwich, in the county of Chester.
The salt, however, which is thus easily procured, and in very large masses, by no means affords a sufficient supply: hence numerous persons are employed in extracting it from sea-water, or from saline springs.The former yields only from one-50th to one-30th part of its weight, but the latter produce the greatest quanti-ties; and we are informed by Dr. Browning (Art of Making common Salt, etc. 8vo.), that the celebrated saline springs of North-wich, Nantwich, and Droitwich, in Cheshire (whence Great Britain is principally supplied), contain more than one-sixth part of good salt.
Common salt is obtained from these natural solutions by two different methods : First, the saline fluid is speedily evaporated, till the salt begin to concrete, and settle in the form of grains at the bottom of the pans ; after which it is put into proper vessels for draining the brine; and, when the process is completed, it is called bay-salt. By the second method, the evaporation is slow and gradual; so that it is continued only till a saline crust is formed on the surface of the liquor; which soon shoots into crystalline cubes.
In the first volume of the Trans-actions of the Royal Sociey of Edin-burgh, we meet with a memoir, by the Earl of Dundonald, contain-an account of a new expedient of purifying.sea-salt. He observes that the common salt is mixed with various substances, which in a measure render it unfit for the important purpose of preserv ing food ; and which appear from experiments to be nauseous, bitter. and cathartic salts, with earthy bases. And, as the mode of purifying salt by dissolution in Water, and precipitation of the earthy matters with fossil alkali, is not only too tedious, but also too expensive for common use, Lord D. proceeds on the fact, that hot water, when saturated with sea-salt, will still dissolve some portion of bitter salts. He, therefore, directs the small end of a funnel, or similar vessel, which is perforated, to be placed downwards ; filled with sea-salt, and kept in a moderate heat. One 20th part of such salt is now to be dissolved in the smallest possible quantity of boiling water, which must be poured into the cone, that contains the remaining 19 parts. The boiling water, being thus saturated, will not take up any more salt, but liquefy a considerable part of the bitter, earthy, or saline particles, which consequently will ooze out at the hole. When this solution ceases to drop, the process must be repeated, by using fresh portions of the same parcel of salt thus partially refined, till the requisite degree of purity be obtained. Lord Dundonald is of opinion, that three washings will lender the British salt much purer than that obtained from any other country : - the superiority of such salt is evident both to the taste, and for its effects in preserving animal food and butter. This is an object of the greatest importance, and from the simplicity, facility, and cheapness of the above stated process, we trust it will shortly be introduced into more general practice. - Various other, though more, complicated attempts, haye lately been made by private individuals, to expedite and improve the preparation of salt, as well as to decompose it with a view to extract the soda : among these, we shall mention only the following patents : namely, Mr. GeoRge HOdson's, obtained in August, 1792, for his new method of separating fossil alkali from common salt; and also of separating the same substance from ;kelp ; his second patent, granted in February, 17971 for an improved mode of effecting the same object; and likewise of extracting the mineral alkali from the muriatic acid, contained in rock-salt, common salt, brine, etc; - Mr. James Manley's patent, dated July, 1801, for various improvements in the process of manufacturing salt. As, however, these different processes would not be generally interesting, and could be understood only by the aid of engravings, the inquisitive reader will consult the 2d, 10th, and 15th volumes of the Repertory of Arts, etc.
Uses : The value of salt for culinary purposes is well known : it is likewise of peculiar service in preserving the health of cattle (see vol. i. p. 460-7), and particularly in preventing that most fatal disorder in sheep, the rot (see vol. iii. p. 510-11). Besides, salt is an excellent manure ; as it is equally destructive to weeds and vermin : the most accurate proportion appears to be sixteen bushels per acre; but, if that quantity be exceeded, or doubled, it will produce effects diametrically opposite to those intended, and completely check vegetation.
With respect to its medicinal properties, common salt, when taken in small quantities, promotes the appetite and digestion 5 but, if given in large doses, for instance, half an ounce, it operates as a laxative. It deserves, however, to be remarked, that its useful pr are greatly changed in a state of intimate combination with animal matters: thus, silt-batter and salt-meat, or fish, are less wholesome than those substances when eaten in a fresh state, with a due portion of that domestic spice ; nay, if used too frequently, the former often lay the foundation of tedious maladies, such as leprosy, scurvy, and other cutaneous eruptions. - Lastly, salt is sometimes administered with a view to restrain the operation of emetics, or to carry them off by stool; and likewise as 3 stimulus in clysters.
A new species of neutral salt has lately been discovered in France, an account of which we have abstracted from M. Chaussier's Memoir, inserted in the 37th No. of the " Recueil Periodique, " a Medical Journal published at Paris. This new salt is the sulphurated hydro-sulphur of soda, and is formed spontaneously in manufactories where the sulphate of soda, or Glauber's Salt (which see) is decomposed, by being melted in a reverbcratory furnace, with a certain portion of iron filings, and carbon or charcoal. Our limits will not permit us to state the whole of this process; we shall therefore only observe, that the sulphurated hydro-sulphur of soda is found in the leys which remain, after the carbonate of soda has been obtained by ebullition. Such leys being suffered to stand for some time, a crystallization takes place in the residuum ; and the crystals appear of a dusky yellow colour, being sometimes soiled, or tinged with a black powder, adhering to their surface: these are ne\t thrown into a proper quantity of water ; and, when almost dissolved, the fluid is strained and deposited in a cool place, when the saline matter will again be Thus purified, the salt forms large transparent crystals, having a fresh taste, which speedily becomes somewhat bitter: it retains its form and properties on exposure to the air, neither deliquescing, nor crumbling into powder.
M. CHaussier has successfully administered this neutral salt in cases of inveterate herpetic affections, which were not accompanied with fever or inflammation : he observes, that it may also be prescribed in certain intestinal diseases, occasioned by metastases, or the repulsion of a psoric and scorbutic virus. - The doses must at first be small, and gradually increased ; while the efficacy of the drug may be promoted by diluents, or such drinks as are best calculated to alleviate the situation of the patient.