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.” ADULTERATIONS. The ordinary acid of the shops contains in general 3 or 4 per cent. of saline matter, which consists of about two-thirds of sulphate of potass, and one-third of sulphate of lead. Dr. Ure observes, that even more is occasionally found, in consequence of the employment of nitre to remove the brown colour given to the acid by carbonaceous matter; the amount of adulteration, he observes, may be readily determined by evaporating a definite weight of the acid in a small capsule of platinum; these impurities however in a medical point of view are immaterial, since they are at once separated by dilution, but in a commercial sense they deserve attention, as their presence considerably increases the specific gravity of the acid. Dr. Ure is of opinion that genuine commercial acid should never exceed 1·8485, and that any density beyond this is the effect of saline combination. _Journal of Science and the Arts, No. 7._ ACIDUM SULPHURICUM DILUTUM. L.E.D. Dilute Sulphuric Acid.