It is much to be regretted that the proportion of water directed for the dilution of the acid, varies considerably in the different pharmacopœias; that prepared according to the Edinburgh and Dublin formulæ, being in strength to that of the present Pharmacopœia of London, as 4 to 1: _specific gravity_, 1·080; each fluid-drachm contains nearly 8½ grains of the concentrated acid, and saturates 18 grains of crystallized sub-carbonate of soda. DOSE ♏︎x to xl. The acid is a very powerful anti-phlogistic remedy; it has been much extolled in diseases of the liver, and in syphilis. Mr. Pearson however observes that we ought not to rely upon it in any form of lues venerea, although it may be often serviceable in restraining the progress of the disease when an impaired constitution or other circumstances render the exhibition of mercury improper; when sufficiently dilute, it forms an excellent lotion for old indolent ulcers. It proves also expectorant, see _Form. 139, 140_; and it is occasionally used with success for the purpose of counteracting the consecutive effects of opium. See _Form. 16_.
QUALITIES. A liquid emitting fumes of a flame-red colour, and of a very pungent and remarkable odour. The acid is either blue, green, straw-coloured, clear orange yellow, according to the proportion of nitrous acid gas[353] with which it is charged. CHEMICAL COMPOSITION. This acid is improperly denominated _Nitrous_, for it is nitric acid, holding nitrous acid gas loosely combined; by dilution this last constituent is disengaged, and the acid, after passing through a succession of different colours, becomes pure nitric acid; the application of a gentle heat effects the same changes.
ACIDUM SULPHURICUM. L.E.D. Sulphuric Acid.
QUALITIES. _Form_, a thick liquid of an oily consistence, specific gravity 1·85; a fluid-ounce weighs a fraction of a grain more than fourteen drachms. _Colour_, none, but it acquires a brown tinge from the smallest portion of carbonaceous matter; mere exposure to the air is sufficient for this purpose, in consequence of the acid disorganizing and carbonating the vegetable and animal matter suspended in the atmosphere; it is therefore evident that bottles in which it is preserved ought not to have stoppers of cork, but those of glass. CHEMICAL COMPOSITION. Like the other mineral acids, it has never been obtained in an insulated state without water; according to Davy, the composition of the strongest acid may be thus expressed: sulphur 30, oxygen 45, water 17. It has a very powerful affinity for water, and produces when mixed with it a very considerable heat; exposed to the atmosphere it imbibes at least seven times its own weight of water, and so rapidly as to double its weight in a month; when of the specific gravity 1·85, it rises in vapour at about 550°, and distils unaltered, whereas weaker acids lose water by being boiled, and are brought to that degree of concentration; when diluted with 12 or 13 per cent. of water, an acid results of the specific gravity 1·780, and in this state of dilution it boils at 435°, and freezes sooner than water; a knowledge of this curious fact suggests to the prudent chemist an important precaution; Mr. Parkes, in his Chemical Essays, vol. ii. relates the occurrence of a terrible accident which happened in consequence of this circumstance not having been attended to.—“Carboy after carboy burst by the expansion of the acid in the act of freezing, and had not the packed carboys that remained been immediately immersed in tepid water, not a single one would have escaped the general wreck.”