Flowers are to be dried nearly as leaves, but more quickly, and with more atten tion. As they must not be exposed to the sun, it is best done by a slight degree of artificial warmth. When they lose their colour and smell they are unfit for use.
Seeds and fruits, unless when other wise directed, are to be gathered when ripe, but before they fall spontaneously. Some pulpy fruits are freed from their core and seeds, strung upon thread, and dried artificially. They are in general best preserved in their natural coverings, although some, as the colocynth, are peeled, and others, as the tamarind, pre served fresh. Many of these are apt to spoil, or become rancid; and as they are then no longer fit for medical use, no very large quantity of them should be collected at a time.
The proper drying of vegetable sub stances is of the greatest importance. It is often directed to be done in the shade, and slowly, that the volatile and active particles may not be dissipated by too great heat; but this is an error, for they always lose infinitely more by slow than by quick drying. When, on account of the colour, they cannot be exposed to the sun, and the warmth of the atmosphere is insufficient, they should be dried by an artificial warmth, less than Fahren heit, and well exposed to a current of air. When perfectly dry and friable, they have little smell; but after being kept some time, they attract moisture from the air, and regain their proper odour.
The boxes and drawers in which vege table matters are kept, should nut impart to them any smell or taste; and more .cer tainly to avoid this, they should be lined with paper. Such as are volatile, of a delicate texture, or subject to suffer from insects, must be kept in well covered glasses. Fruits and oily seeds, which are apt to become rancid, must be keptin a cool and dry, but by no means in a warm or moist place.
Oily seeds, odorous plants, and those containing volatile principles, must be collected fresh every year. Others, whose properties are more permanent, and not subject to decay, will keep for several years. Vegetables collected in a moist and rainy season are in general more watery and apt to spoil. In a dry season, on the,
contrary, they contain more oily and re sinous particles, and preserve much bet ter, Alechanical Operations.
These consist of the mode of deter mining the weight or measure of bodies; their division into minute particles; their separation of part from part, or of the useful from the useless; the modes of intermixing them.
Weights and Measures. The quantities of substances employed as medicines are determined with the greatest accuracy by weighing. The scales should balance with the utmost precision, and turn with the utmost facility. Balances should be defended as much as possible from acid and other corrosive vapours, and not be unnecessarily suspended, ast heir delicacy of decision is hereby much impaired; and to guard against this last evil in another way, they should never be over-loaded.
The want of an uniformity of weights And measures, which is felt in every coon try, and in every branch of trade and commerce, is of peculiar inconvenience in pharmacy. All our college pharmaco poeias command the use of troy weight; yet the wholesale druggists in every in stance, excepting where a very small portion of an article is bought by grains, scruples, or drachms, sell by avoirdupoise weight; and there is reason to fear that, both amongst apothecaries and druggists, most of the pharmaceutic compositions are prepared by this last division; in con sequence of which it is impossible for the physician to know the exact strength of the dose he prescribes; and if he do, he cannot often obtain it in the proper pro portions of its respective ingredients. The difficulty is still increased by is pro miscuous use of weights and measures, in determining the quantities of fluids; on which account, though the London col lege still authorises both fbr distinct pur poses, the colleges of Edinburgh and Dublin have rejected measures altogether.
For measuring fluids, the graduated glass measures are always to be preferred: they should be of different sizes, accord ing to the quantities they are intended to measure. Elastic fluids are also measured in glass tubes, graduated by inches and their decimals.