of fresh leaves, and making ultimately four ounces of the menstruum, of which from ♏︎xxx to fʒj every six hours may be given until a sedative effect is produced. See _Oleum Amygdalæ Amaræ_. INCOMPATIBLE SUBSTANCES. Hydro-cyanic acid is decomposed by most of the _oxydes_ usually employed in medicine, particularly by those of _Mercury_ and _Antimony_. The alkalies do not appear to diminish its efficacy. _Nitrate of Silver_, and the salts of iron occasion precipitates; nor ought the _sulphurets_, the _mineral acids_, or _chlorine_ to enter with it into prescriptions. DOSE. Of the medicinal, or _diluted_ hydro-cyanic acid, ♏︎ij,–viij. There is however considerable difficulty with regard to the strength of the dilute acid employed in medicine, since the density is a criterion of greater nicety than can be conveniently used by the majority of practitioners; in fact, as Dr. Ure has observed, the liquid at 0·996, contains about double the quantity of real acid, which it does at 0·998. Dr. Ure has accordingly proposed another test of the strength of this powerful and dangerous medicine, which is not only easier in use, but more delicate in its indications;[347] it is as follows. To 100 grains, or any other convenient quantity of the prussic acid, contained in a small phial, add in succession, small quantities of the peroxide of mercury, (the common _red precipitate_ of the shops) in fine powder, till it ceases to be dissolved on agitation. The weight of the red precipitate taken up, being divided by four, gives a quotient representing the quantity of real prussic acid present. By weighing out before hand, on a piece of paper, or a watch glass, forty or fifty grains of the peroxide, the residual weight of it shews at once the quantity expended. The operation may always be completed in five minutes, for the red precipitate dissolves as rapidly in the dilute prussic acid, with the aid of slight agitation, as sugar dissolves in water. ADULTERATIONS. If, says Dr. Ure, the presence of muriatic acid be suspected, then the specific gravity of the liquid compared with the gravity of the peroxide dissolved, will shew how far the suspicion is well founded; thus if 100 grains of acid, specific gravity 0·996, dissolve more than 12 grains of the red precipitate, we may be sure that the liquid has been contaminated with muriatic acid. _Nitrate of Silver_, in common cases, so valuable a reagent for muriatic acid, is unfortunately of little use here, for it gives with prussic acid, a flocculent white precipitate, soluble in water of ammonia, and insoluble in nitric acid, which may easily be mistaken by common observers, for the _chloride_ of that metal. But the difference in the volatility of prussiate and muriate of ammonia may be had recourse to with advantage; the former exhaling at a very gentle heat, the latter requiring a subliming temperature of about 300° _Fah._ After adding ammonia in slight excess to the prussic acid, if we evaporate to dryness at a heat