℞. Tincturæ Iodini ♏︎v. Aquæ destillat: f℥j =N.= Sumr: guttæ x ter quotidie. 6. ℞. Quinæ Sulphat: gr. ij Acid: Sulphuric: dilut: ♏︎ij =L.= Aquæ destillat: f℥j Fiat Haustus, bis terve de die sumend: OF THE MEDICINAL DYNAMETER. This instrument is capable of showing, on mere inspection, the absolute as well as relative strengths of the different Officinal Preparations of the Pharmacopœia. The active Principles, or Medicinal Bases, are distinguished by CAPITAL LETTERS, placed in coloured compartments, and each Officinal preparation is marked by a line corresponding in colour with that of its active ingredient. Where a preparation contains two active ingredients it is distinguished by two coloured lines, as may be seen in the _Pulvis Ipecacuanhæ comp_. By this expedient the eye, at once, recognises the different classes of medicines; all those, for instance, coloured _red_ are Opiates; those _blue_, Mercurials; _green_, Acetic acid; &c. The introduction of colours, moreover, immediately indicates the basis to which any preparation refers, and thus prevents the possibility of doubt or confusion. If we wish to learn the actual quantity of active matter contained in any given proportion of a compound, we have only to turn the scale until the name of such compound coincides with the number in question, when the figure opposite to the basis solves the problem; thus—how much opium is contained in 5 grains of the _Pulvis Ipecacuanhæ compositus_? By having brought this preparation to 5, we shall see ½ opposite to Opium, denoting that such a number of grains contains half a grain; for, unless it be otherwise expressed, the figures denote _grains_ for the solids, and _minims_ for the liquids. And, since the number opposite to the Base denotes the absolute quantity of it contained in those several proportions of its Officinal compounds, which are expressed by the respective numbers opposite to each, it follows that these latter must all be medicinally equivalent to each other; thus we have seen that 5 grains of _Pulvis Ipecacuanhæ compositus_ contains ½ grain of Opium, if we turn our eyes to the other Opiate preparations we shall perceive that each has a different number opposite to it, these figures show the number of grains of each which contains ½ grain of opium, and consequently those numbers must be all Equivalents; thus 2½ grains of _Pil. Saponis comp:_ 5 grains of the _Pulv: Corn: ust: cum Opio_, 9½ minims of Tinctura Opii, 10 grains of _Pulv: Kino comp:_ 18 grains of _Confectio Opii_, 20 grains of _Pulv: Cretæ comp: cum Opio_, and 120 minims, or two fluid-drachms of _Tinctura Camphor: comp:_ contain half a grain of Opium, and are consequently all equivalent to each other. This system of Equivalents will be found of much practical value to the