The practice has been recommended of making certain emulsions by very carefully smearing the bottle with the emulsifying agent. But it has been generally condemned, as not being an effectual method. Copaiba forms an exception, and the balsam may be as well emulsified in this way as by any other.

Rotate the mucilage in the bottle, well covering the inside. Add the copaiba by degrees; perfectly emulsify by adding the alkali, previously diluted with 3 drachms of cinnamon-water ; then add the rest of the cinnamon-water by degrees, retaining or allowing for 2 ounces with which to cleanse the measure from both the liquor potassae and the spirit of nitrous ether, which should be added last.

Some prescribers are particular in the exhibition of copaiba, and occasionally want it to be taken without other ingredients. It can be so prepared, or made to combine at pleasure in all strengths by using freshly made thick mucilage ; thus :

Extractum filicis liquidum and tinctura cannabis indicae may both be compounded in the same manner.

Notes.

Glycerin, like an alkaline salt, is a disturbing agent in an emulsion when another emulsifier is present. Many salts spoil emulsions when they are either neutral or acid, but when alkaline they favour the process. Borax has a beneficial action in the absence of acacia, and is in itself an excellent emulsifying agent.

Professor Redwood used to say that mucilage answers better than an alkali for making an emulsion with castor oil or copaiba, but that the alkali is best for oil of almonds. Moreover, a good emulsion of oil of almonds and alkali is spoiled by the addition of mucilage. This the late Mr. Ince confirmed from constant disappointment.

M. Constantin (in 1854) advocated what may be called the ignition process for emulsion of the gum resins and resins. He took a weighed quantity of gum resin, and, having placed it in a mortar, added about four times its weight of alcohol. The spirit being ignited, the whole was triturated until all the alcohol was burned away. The gum resin became a soft extract; the liquid was then added in small quantities at a time, and a perfectly homogeneous emulsion was produced without subsequent separation. In the case of resins they must be converted into gum resins by the addition of powdered gum arabic. To the resin- balsam of tolu, for instance- twice its weight of gum arabic is to be added, and alcohol used in the same way. The peculiar taste and odour remain undiminished. The method is expensive, but quite successful.

With the softer resins and gum resins trituration in a hot mortar gives pretty much the same result as regards facilitating procedure in emulsirlcation, and there is less risk of any of the volatile constituents being dissipated. See procedure of analogous kind in mixture of Indian hemp extract and chalk mixture on page 311.