The objects to be obtained in these preparations are the following: -
1. A preparation containing all the soluble ingredients of the substance employed.
2. A uniform strength, so that it may be always known exactly how much of the dry crude material is represented in-a given measure of the tincture.
3. A fixed alcoholic strength, so that in making dilutions all decomposition may be avoided, by using a spirit of the same alcoholic strength as that existing in the tincture.
These objects may be attained in the following manner: -
1. The complete solution of all soluble matter can be accomplished by varying the alcoholic strength to suit the nature of the ingredients in each plant; using a very dilute spirit where the ingredients are chiefly soluble in water, and a strong spirit where alcohol is the best solvent. Also, by using a sufficient quantity to insure the complete exhaustion of the plant.
2. The uniform strength of tincture is advisable for many reasons, and especially in connection with the making of attenuations. Hitherto the mother tinctures made from fresh plants have varied greatly in strength, not only among themselves, but the tincture of the same plant differed from time to time according to whether the fresh plant chanced to be more or less juicy. In consequence of this, the lower attenuations have varied in strength, since in every instance the same number of drops of mother tincture were added to a given quantity of spirit. To obtain uniformity it is necessary to ascertain the quantity of moisture contained in the fresh plant, and to allow for this in making the tincture.
In every instance the dry crude substance is taken as the starting-point from whence to calculate the strength, and, with very few exceptions, the mother tinctures contain all the soluble matter of 1 ounce of the dry plant in 10 fluid ounces of the tincture.
3. It will be noticed that a series of tables are given at the close of the Tincture Process, by means of which the pharmaceutist can calculate the exact quantity and strength of spirit which he has to use in the case of each medicine. The necessity for these tables is owing to the water present in the fresh plant mixing with and diluting the spirit employed in making the tincture, so that the quantity of the spirit used should vary according to the percentage of moisture in the plant. By careful attention to these tables, uniform products may be obtained from all plants, notwithstanding their variableness of moisture; and also by diluting the matrix tinctures with a spirit of the same strength, dilutions may be always made of the same medicinal value.