Cod-liver-oil emulsions have long been prepared with Irish moss. Mr. Peter Boa (Edinburgh) obtains a clear mucilage of the moss by straining the mucilage through absorbent cotton-wool supported on muslin in a hot-water funnel. The mucilage itself is prepared by digesting \ ounce of washed moss in 24 ounces of water for an hour, boiling for five minutes, and straining the moss mucilage. It serves as well as acacia for chalk mixture. For suspending copaiba it is superior to acacia- separation taking place much more slowly and less completely. Part of the copaiba remains in an emulsified state at the bottom of the bottle when moss is used, but with acacia the whole rises to the top. For emulsifying cod-liver oil it is greatly superior to acacia in preventing separation, but finer division of the oil is obtained with acacia. Moss mucilage 3vj., cod-liver oil and water 3ij. produce an emulsion that does not readily separate. Using 3vj. acacia mucilage, cod-liver oil, and 3ij. water, the resulting emulsion soon separates. Irish-moss mucilage is not good for suspending heavy powders, such as bismuth subnitrate. It keeps well in full bottles. One of the chief drawbacks to the use of Irish moss in preparing extemporaneous emulsions is its variability. Every new supply requires to be standardised, so to speak. By the aid of strong machinery it breaks up oil very finely and it retains a tenacious grip of it. An emulsion made with it is less easily put out of gear than an emulsion made with gums or egg. Its employment is restricted mainly to manufacturing circles.

Malt Extract is considerably used for emulsifying cod-liver oil without any other emulsifier. The plan is to use a mortar which has been warmed well by filling with boiling water, the pestle also being warmed in the water ; put the extract in the mortar, stir to liquefy it, and add the oil in small portions at a time, stirring well. The oil may be mixed with liq. calc. sacch. in the proportion of 5 minims to 1 ounce.

Gelatin has also been proposed as an emulsifying agent, especially for paraffin oils, and was the subject of a patent (No. 3466, 1886). According to this patent a solution of gelatin or other similar substance is made, in the proportion of 4 ounces to the gallon of water. In 12 parts of this 1 part of phosphate of soda or potash, or carbonate of soda or potash, is dissolved by the aid of heat, and this mixture is capable, by the ordinary means, of emulsifying from 24 to 36 parts of animal or vegetable oils. For embrocations ammonia is substituted for the above-named salts. Chloroform and such liquids may be emulsified in this manner. For mineral oils and the like the alkali is replaced by soft soap. For example, an emulsifying solution is made with 6 ounces of concentrated size, 1 pound of soft soap, and 1 gallon of water, and this mixture is capable of emulsifying 2 gallons of paraffin oil. The following is an excellent example of the utility of gelatin:

The prescriber expected this to form an emulsion, but it does not. Acacia gum, milk, and gelatin were tried as the emulsifiers, and the best results were obtained with 1 1/2 part of gelatin. This was soaked in 20 of the water, dissolved by gentle heat, the glycerin added, and 3 or 4 drops of liquor potassae to neutralise the acids in the tar. The oil of cade was then added by degrees, stirring constantly, the emulsion diluted with 30 of water; and finally the liq. plumbi was added, diluted with the remainder of the water.

Senega-root and Quillaia-bark contain a principle (saponin) which possesses powerful emulsifying properties and imparts to infusions of either of these drugs the frothing property which is not the least important of their characteristics. The late Mr. H. Collier, of Guy's Hospital, studied the use of a tincture of quillaia made by digesting 4 ounces of the coarsely powdered inner bark in 20 ounces of rectified spirit for a week, then filtering, but a proof-spirit tincture is equally good. This tincture is peculiarly valuable for converting an oil into an emulsion in presence of an acid; for example:

This forms a very good emulsion.1 Ext. filicis maris is a troublesome substance to emulsify, milk being one of the best vehicles. Although it may with care be turned into a perfect emulsion with acacia, the mixture is not at all pleasing in character. The following is, however, all that can be desired:

1 The tincture varies in saponin-content according to the alcoholic strength of the menstruum, and saponin per se is most reliable : 1/4 grain of saponin and 2 grains of powdered tragacanth emulsify 1 ounce of any fixed oil with 1 ounce to I 1/2 ounce of aqueous vehicle.

Oil of turpentine works well with its own measure of the tincture, e.g.:

Resinous tinctures require more than their own volume of the quillaia tincture to prevent separation of resin; thus:

Misce.

After a short time the resin deposits, but it readily diffuses on shaking. It will be found that in cases of this kind acacia acts better- it gives viscosity to the liquid, and thus helps to retain the separated resin. For the same reason acacia or tragacanth is better for resin of copaiba than quillaia- in fact, quillaia is at its best with oils and oleo-resins, and should be avoided for resins.

The rectifled-spirit tincture is used in the preparation of liquor picis carbonis, the full-strength spirit being required to dissolve the coal-tar, and the quillaia to emulsify the mixture when it is mixed with water.