310
ELEMENTS OF MATERIA MEDICA.
I
Properties. —It crystallizes in colourless cubes, or more rarely in :regular octahedrons. In the salt pans the little cubes are frequently soaggregated as to form hollow, four-sided pyramids, whose sides havesome resemblance to a series of steps: these are technically calledhoppers. The specific weight of salt is 2T7. The taste is pure saline.When free from all foreign matters, chloride of sodium is permanent inthe air, but ordinary salt is slightly deliquescent, owing to the presence ofsmall quantities of chloride of magnesium. When heated it decrepitates(more especially the coarse-grained or bay salt), at a red heat fuses, andat a still higher temperature volatilizes. Rock salt is transcalent ordiathermanous : that is, it transmits radiant heat much more readily thanmany other transparent bodies, as glass. It is soluble in water, andslightly so in alcohol. Hot and even boiling w ater dissolves very littlemore salt than cold water. At 60° it requires about twice and a half itsweight of water to dissolve it.
Characteristics. —Its characters as a soda salt are the following:—
It produces no precipitate with the hydrosulpliurets, ferroeyanides, phos-phates, or carbonates. Prom the salts of potash it is distinguished bycausing no precipitate with perchloric or tartaric acid, or with chlorideof platinum, and by the yellow tinge which it communicates to the flameof alcohol. As a chloride it is known by nitrate of silver throwingdown a wiiite precipitate, soluble in ammonia, but insoluble in nitricacid. Lastly, chloride of sodium is odourless, and devoid of bleaching jproperties.
Composition. —Pure chloride of sodium has the following composition:
Eq. Eq.Wt. Per Cent. Ure.
Sodium. 1 .... 24 ... . 40 ... . 39*98
Chlorine.1 .... 36 ... . 60 ... . 60*02 ;
Chloride of Sodium.I .... 60 ... . 100 .... 100*00
The crystals contain no w r ater in chemical combination with them, but alittle is frequently mechanically lodged between their plates.
Impurities. —The commercial salt of this country is sufficiently pure jfor all dietetical and therapeutical purposes ; and its low' price is a <sufficient guarantee against its adulteration. In France , however, serious \accidents have happened in consequence of the use of sophisticated salt. I(Christison ’s Treatise on Poisons, 3d ed. p. 604, and Devergie, Med. Leg. 't. ii. p. 876.)
Physiological Effects. («.) On vegetables. —In minute quantitychloride of sodium is injurious to very few, if any, plants, and to some itappears to be beneficial. Used moderately it is a most excellent manureto certain soils. In large quantities it is injurious, though unequally so,to all plants. (Davy, Agricult. Chem. , and Decandolle, Phys. Veg. pp. 1262 i.and 1343.) ij
(A) On animals. To marine animals common salt is a necessary con- •stitueut of their drink. It is relished by most land animals. “ The jeagerness with which many quadrupeds and birds press towards salt jsprings and lakes, situated in inland districts, for the purpose of tasting jtheir contents, indicates,” says Dr. Fleming, ( Philosophy of Zoology, vol. i.p. 316) “ a constitutional fondness for salt.” In the Ruminantia the Jsalutary effects of salt are especially observed. “ They contribute power- |