Mixtures are liquid preparations intended for the administration of a medicinal substance or substances either in solution or suspension, and compounded in such a manner as to ensure perfect distribution throughout the bulk, with a view to accuracy of dose. Mixtures containing alkaline substances in the presence of vegetable colouring matter usually darken on keeping. To ensure uniformity of colour when dispensed at different pharmacies, such mixtures should be prepared freshly as required. Mixtures containing volatile principles, if intended to be stored, should be kept in small well-filled bottles, in a cool place. Mixtures prepared with infusions or preparations containing an appreciable amount of vegetable extractive, if intended to be kept, require the presence of a preservative, such as emulsion of chloroform (about 10 minims to each fluid ounce), alcohol, glycerin, or an alcoholic tincture (about ½ fluid drachm to each fluid ounce). Mixtures prescribed in concentrated form, or containing potent doses of medicament, and mixtures intended for administration to children or infants, should be made up to the exact volume prescribed, and dispensed in a bottle, bearing, in addition to the prescribed directions, instructions that each dose be measured in a properly graduated glass. The doses indicated by graduated bottles (especially short bottles bearing several graduations) are rarely sufficiently uniform for the administration of potent mixtures. By means of the larger sizes of graduated bottles more uniform doses can usually be measured, and these form a sufficiently accurate approximation to the intention of prescribers as regards the administration of ordinary forms of mixtures. For references to the uses of suspending agents, see monographs upon Acaciae Gummi and Tragacantha, or names of substances or preparations which require suspension when exhibited in mixture form.