This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Extract of Hemp (Extractum Cannabis), as recognized in the U. S. Pharmacopoeia, is prepared by treating the dried tops with alcohol, and evaporating the tincture thus obtained. But it may also be procured by purifying the crude churrus of the Hindoos, by dissolving what is soluble of it in alcohol, allowing the undissolved impurities to subside, and then decanting and evaporating. In this way is prepared the Purified Extract of Hemp (Extractum Cannabis Purificatum) of the U. S. Pharmacopoeia. A still purer form of it is prepared by a somewhat complicated process, for an account of which the Dispensatories may be consulted. One of the best tests of its strength, independently of actual trial, is its possession, in the highest degree, of the characteristic properties of smell and taste. Prof. Procter, who has specially investigated the subject, gives as its characteristic properties, its peculiar smell when slightly heated, its indifference to the alkalies, and its solubility in alcohol, ether, chloroform, benzole, and oil of turpentine; but the best test. he thinks, is nitric acid, which acts on it slowly when Cold, but rapidly with heat, giving out red fumes, and converting the resin into an orange-red substance, which, when washed and dried, closely resembles gamboge in colour. (U. S. Dispensatory, 12th ed).
The dose of the extract varies extremely, in consequence of the variable strength of the preparation. When of the best quality, half a grain of it will produce obvious effects, while ten or twelve grains are often required, and sometimes the drug is quite inert. It is best, as a general rule, to begin with one grain or less, which may be repeated every two, three, or four hours, until its effects are produced; and, if none can be obtained from this dose, gradually to increase it, until the amount is ascertained in which the parcel employed will act. In tetanus, ten grains may be given every half hour till it operates, and the quantity increased, if necessary. It may be administered in pill or emulsion. The latter is the preferable form, where speedy effect is required. It may be made by rubbing the extract up with a little olive oil, and then suspending it in water, or one of the aromatic waters, by means of gum arabic and sugar.
Tincture of Hemp (Tinctura Cannabis, U.S.; Tinctura Cannabis Indicae, Br.) is made by dissolving six drachms of the extract in a pint of officinal alcohol (sp. gr. 0.835). The dose, equivalent to one grain of the extract, is about 20 minims or 40 drops. Dr. O'shaugh-nessy gave 10 drops of the tincture every half hour in cholera, and a fluidrachm as often in tetanus, until the desired effects were produced, or the medicine showed decided signs of acting on the brain. This is among the substances which have been used in the form of spray, as made by the atomizer; from five to ten minims being mixed for the purpose with a fluidounce of water. It has been inhaled for the relief of nervous or spasmodic cough, and that attendant on phthisis. It has also been used hypodermically for the general effects of the medicine, in the dose of from ten to twenty drops.