I. Substances which are capable of entering into chemical combination, or of decomposing each other, ought not to be mixed together, unless it be with a view of obtaining the new products as a remedy.
II. Transparency is not a necessary condition,[[302]] and hence insoluble powders may be advantageously introduced into mixtures, if the following precautions be observed.
1. They must be divisible and mechanically miscible in the liquid.
2. They must not possess too great a specific gravity.
3. They must not render the liquid too mucilaginous or thick; thus, f℥j should seldom contain more than ʒss of a vegetable powder, ℈ij of an electuary, and conserve; or grs. xv, or ℈j of an extract.
III. The taste, the smell, and the general aspect of the mixture should be rendered as pleasant as possible; thus milk covers the taste of bark, of the tinctures of guaiacum and valerian, and that of lime water; and a light decoction of the liquorice root disguises a bitter taste more effectually than sugar.
The Physician may also produce occasional changes in the appearance of his mixture, in order to reconcile a delicate taste to its continuance; he never ought however to alter the essential part of plans which he finds advantageous.
A Draught differs merely from a mixture in quantity; it is usually taken at once, and should not exceed f℥iss; it should be always preferred when,
1. The remedy is to be taken in a precise dose.
2. Whenever it is liable to spontaneous decomposition.