[294] An apparatus similar to that used for ice-cream.
Obs. When water, acidulated with acetic acid, is employed in the preparation of extracts, the vegetable substances are usually macerated in it, in the cold, or the dilute acid is sprinkled over the bruised plant in the fresh or recent state, and the whole is then submitted to strong pressure, to expel the juice, which is strained and evaporated in the usual way, but preferably in a well-tinned or plated-copper pan.
Alcoholic and SPIRITUOUS EXTRACTS are prepared by evaporating a filtered concentrated tincture of the ingredients in any suitable vessel, by which the volatilized spirit may be saved. In general, rectified spirit is used as the menstruum; but in some cases proof spirit is employed; and, in others, the substances are first digested in proof spirit, and afterwards in water, and the mixed tincture and infusion evaporated in the usual manner.
Ethereal extracts are obtained in a similar manner to alcoholic ones; but being merely prepared in small quantities at a time, the process may be conveniently performed in glass vessels. When it is required to boil either of the above fluids (alcoholic or ethereal), or any other volatile liquid on the ingredients, a vessel fitted with a long tube, or a Liebig’s condenser reversed, as noticed under ether, may be used to prevent any loss of the menstruum.
The INSPISSATED VEGETABLE JUICES (JUICES, E.; SUCCI, L.) of the British Pharmacopœia are obtained by expressing the juices from the fresh plants, and preserving them by the addition of spirit. “By thus preserving the juice of the plant its properties are not impaired by the action of the air during the time necessary to dry the leaf for tincture, nor by the action of both air and heat during the time necessary to evaporate the juice to the consistence of an extract.”—Squire. The directions of the Edinburgh College for preparing their inspissated juices (SUCCI SPISSATI,
L.) are—“Beat the fresh substance, and press it strongly through a canvas bag, in order to obtain the juice; which, being put into a wide, shallow vessel, and heated by means of boiling water saturated with sea-salt, is to be reduced to the consistence of honey. The mass, when cold, is to be put into glazed earthen vessels, and moistened with strong alcohol.” By operating in this way a considerable portion of the activity of narcotic vegetables is lost. Some of their juices, as that of aconite, are impaired in so short a time as scarcely to compensate for the trouble of preparing them. This deterioration does not, however, take place in any remarkable degree, if the expressed juice from the recent vegetable be evaporated by exposing it in a thin stratum to a current of very dry air, as adopted by Mr Squire. This may be managed by putting the juice into small, flat trays or dishes, placed on shelves in a suitably arranged apparatus, alternated with similar vessels of concentrated sulphuric acid; or by causing a current of very dry air, at the common temperature of the atmosphere, to pass over them. It has been shown that 10 gr. of extract, thus prepared, were more than equal to 20 gr. prepared in vacuo; and to more than 60 gr., and in some cases, 90 gr., of those prepared by the common process of boiling down the juice to an extract.
The concluding portion of the process of extract-making, technically termed ‘finishing-off,’ requires the most scrupulous attention. As the evaporation advances, the heat should be lessened, and as soon as the extract acquires the consistence of thick treacle it should be removed altogether, and the remainder of fluid matter evaporated by the heat retained by the copper pan, the escape of vapour being promoted by assiduous and laborious stirring with a suitably shaped wooden spatula. This part of the process should be continued until a proper consistence is attained and the extract is nearly cold. When high-pressure steam or a chloride of calcium bath is employed, care must be taken to withdraw the heat before stirring the semi-liquid mass; as, if an extract having a temperature of about the boiling-point of water, or even a few degrees below it, is agitated, it becomes full of bubbles, and appears rough and puffy, and this appearance cannot be removed by subsequent stirring, or by any method but redissolving it in water and re-evaporation. This is especially the case with the extracts of sarsaparilla (simple and compound), gentian, liquorice, and most others of a similar class. A good laboratory man knows from experience the proper time for the removal of the heat, but unpractised persons often fail in this particular. In such cases should the heat retained by the evaporating pan, and by the extract, prove insufficient to complete the process, a little more may be cautiously applied. Without assiduous and laborious stirring in the way described, a very smooth and glossy extract cannot be produced. To promote this artificial appearance, some persons add 3% or 4% each of olive oil and gum arabic, dissolved in water, with about 1% or 2% of spirit of wine.
The consistence of the ordinary extracts of the shops is the same as that of electuaries and confections, and is described in the Ph. E. as equal to that of “thick honey.” The instructions of the Ph. L. and D., to evaporate the mass “until it acquires a consistence proper for making pills,” except in 2 or 3 cases (as Ext. Colocynth. Comp., &c.), is not adopted, and, indeed, would be found inconvenient in practice. Extracts evaporated to such a consistence are commonly termed ‘pilular extracts,’ and when evaporated so that they are quite dry, and brittle when cold, they are called ‘hard extracts’ (EXTRACTA DURA, L.).
Pres. Extracts should be put into pots as soon as taken from the pan, and, after being carefully and securely tied over with bladder, should be ‘stored’ in a dry situation. The London College orders “a small quantity of rectified spirit to be sprinkled upon all the softer extracts, to prevent them becoming mouldy.” A better way is to employ a little spirit, holding in solution a few drops of oil of cloves, or a still less quantity of creasote. This should be added to them the last thing before removing them from the evaporating pan, and when they are nearly cold. The same object is effected by moistening the inside of the bladder (used to tie them over) with a few drops of oil of cloves or creasote. Hard extracts should be kept in bladders or gut skins, placed in stone pots, and well covered over. With care, extracts prepared from recent vegetable substances may be preserved twelve months, or from season to season; and those from dry ingredients, or such as are less inclined to spoil, for perhaps double that time; but beyond these periods their virtues cannot be relied on, and they should consequently be discarded, if remaining unused or unsold.
Pur., &c. The quality of an extract cannot be ascertained by mere inspection, nor is it readily discovered by chemical tests. A knowledge of these facts has induced the mercenary and fraudulent manufacturer to employ damaged and inferior drugs in their preparation, alike regardless of the welfare of the patient and the credit of the practitioner. A common practice with some manufacturers is, not only to pick out the least expensive variety of every drug for the preparation of their extracts, but the most inferior and often damaged and worthless portion of this already inferior article. The production of a smooth, bright, and glossy extract is all that is usually attempted by these individuals, and all that is sought after by the mass of purchasers, who mistake the simulation of the mere external signs of good quality for its actual existence. It is a fact, which we can verify from extensive