This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The Pharmacopoeia recognizes three degrees of consistence, namely, 1, like thick honey (Extr. malti); 2, pilular consistence; and 3, dry. In the manufacture of carbonated beverages, fluid extracts are principally employed. The addition of 5 per cent, of glycerine to some extracts, is intended to preserve the proper consistence. Extracts which do not contain any fixed oil or hygroscopic constituents, may usually be reduced to powder when sufficiently evaporated and cooled. On being warmed all extracts become softer, and, if pulverulent at the ordinary temperature, acquire sufficient pliability to be rolled into pills.
"The consistence of extracts nearly neutralizes any injurious effect which contact with the atmosphere might otherwise exert, and the most ordinary care will therefore suffice to keep them unaltered for a considerable time. The sprinkling upon the softer extracts of a small quantity of alcohol has been recommended, but this is entirely unnecessary for those which are to some degree hygroscopic, and of little permanent utility for those which have a tendency to become tough. The difficulty may generally be avoided by spreading a few drops of glycerine over the surface, or, as has been proposed, by working into the warm extract half its weight of glycerine, and dispensing 50 per cent, more than prescribed. This plan has been adopted in principle by the United States Pharmacopoeia, but the glycerine has been reduced to 5 per cent.
"The ordinary extracts are kept in jars of queensware, or, preferably, of porcelain or glass, with a cover of the same material. Small quantities may be kept in wide-mouthed vials with a very narrow shoulder, or in an ordinary tie-over jar, enclosed in a tin box just large enough to receive ' it, and provided with a well-fitting cover to prevent absorption of moisture from the atmosphere, or evaporation of the water contained in the extract. Extracts are rarely liable to mould, unless they contain a considerable proportion of mucilaginous principles, and such are nearly always adapted to be brought to a dry condition. Dry extracts are in most cases preferably reduced to a granular or rather coarse powder. Extracts which have become too soft should be evaporated to the proper consistence by means of a water-bath, and those having become hard and unmanageable should be softened by the heat of a water-bath, when the requisite quantity of distilled water may be incorporated to bring them to the proper consistence.
"For the preservation of fluid extracts, the same precautions are required as for the preservation of most other liquid medicines. The bottles in which they are kept should be provided with a well-ground glass stopper, or with a sound cork, to prevent the slow evaporation of alcohol, which would occasion a change in the solvent power of the menstruum; and they should be placed in a position where they are exposed neither to the direct sunlight, nor to any great or sudden change in temperature. It should be remembered that perhaps all fluid extracts are saturated solutions of some of the principles naturally contained in the drug, and that their re-solution in the fluid extract from which they may have deposited in the cold, can be effected only very gradually at the same temperature at which they previously existed in perfect solution.
"Fluid extracts, if properly made, will fairly represent the drugs, and necessarily must vary in some extent to their efficacy; but the variation should only be within the limits of the variation which is unavoidable in the crude material". - N. D.