Yellow.
Blue.—
| Indigo carmine | 1 part |
| Water | 2 parts |
Mix.
Indigo carmine is a beautiful, powerful, and harmless agent. It may usually be bought commercially, but if it cannot be readily obtained, proceed as follows:
Into a capsule put 30 grains of indigo in powder, place on a water bath, and heat to dryness. When entirely dry put {219} into a large porcelain mortar (the substance swells enormously under subsequent treatment—hence the necessity for a large, or comparatively large, mortar) and cautiously add, drop by drop, 120 grains, by weight, of sulphuric acid, C. P., stirring continuously during the addition. Cover the swollen mass closely, and set aside for 24 hours. Now add 3 fluidounces of distilled water, a few drops at a time, rubbing or stirring continuously. Transfer the liquid thus obtained to a tall, narrow, glass cylinder or beaker, cover and let stand for 4 days, giving the liquid an occasional stirring. Make a strong solution of sodium carbonate or bicarbonate, and at the end of the time named cautiously neutralize the liquid, adding the carbonate a little at a time, stirring the indigo solution and testing it after each addition, as the least excess of alkali will cause the indigo to separate out, and fall in a doughy mass. Stop when the test shows the near approach of neutrality, as the slight remaining acidity will not affect the taste or the properties of the liquid. Filter, and evaporate in the water bath to dryness. The resultant matter is sulphindigotate of potassium, or the “indigo carmine” of commerce.
Tincture of indigo may also be used as a harmless blue.
Green.
Voice And Throat Lozenges.—
| Catechu | 191 grains |
| Tannic acid | 273 grains |
| Tartaric acid | 273 grains |
| Capsicin | 30 minims |
| Black-currant paste | 7 ounces |
| Refined sugar, Mucilage of acacia, of each a sufficient quantity. | |