Oleates

For the preparation of oleates see 'Pharmaceutical Formulas,'page 562, and C. & D., March 30, 1901, page 524. It is important for dispensers to remember that oleates should not be melted in metallic dishes, but in porcelain basins, glass rods or bone spatulas being used to stir or mix them. If the oleates are prescribed for their local effects, and are to be diluted, vaseline is the best diluent; on the other hand, if absorption is not to be retarded, oleic acid should by preference be used, or lard, lanoline, or fixed oil. The oleates of the alkaloids are generally employed without dilution. Most of the metallic oleates are obtainable in the powder form for use as dusting-powder or for making ointments. The following are the accepted strengths of the more common oleates or oleate-ointments:

Aconitine, 1 grain; oleic acid, 49 grains.

Aluminium

Oleate, 1 or 2 drachms, to 1 ounce lard.

Arsenic

Oleate, 20 grains; lard, 1 ounce.

Atropine, 1 grain; oleic acid, 49 grains.

Bismuth Oleate is made into ointments of strengths varying from 5 to 20 per cent, with yellow vaseline as the diluent.

Cocaine, 6 grains; oleic acid, 94 grains. [The B.P. ointment contains cocaine 4, oleic acid 16, lard 80.]

Copper

Ten and 20 per cent, ointments are generally used, the diluent being soft paraffin with a fifth of its weight of hard paraffin added to it. Lard is preferred by some physicians. Melt the oleate with the basis and stir until cold.

Iron

Oleate and lard, equal parts.

Lead

Hebra's ointment is a favourite remedy in skin-diseases. It is generally made by melting lead plaster in its own weight of olive oil, but equal parts of the plaster and vaseline make a much better preparation. Melt the plaster first, then add the vaseline or oil, and perfume with oil of lavender.

Mercury

Precipitated mercuric oleate is now in the British Pharmacopoeia, its ointment consisting of 1 part and 3 parts of benzoated lard. Oleates of mercury and morphine contain 1 grain of the alkaloid in each drachm, irrespective of the mercurial strength.

Nickel

Oleate, 1 part ; lard, 7 parts.

Quinine

One part of the alkaloid dissolved in 3 parts of oleic acid.

Silver

One part of the oleate to 9 parts of lard.

Strychnine

One grain in 49 grains of oleic acid.

Tin

Oleate, 1 part; lard or vaseline, 7 parts.

Veratrine

One grain dissolved in 49 grains of oleic acid.

Zinc

The British Pharmacopoeia ointment is made with precipitated oleate, which in the dry state is largely used as a dusting-powder, generally diluted with boric acid, starch, or talc, or a mixture of these.

Oleates in combination are liable to curious changes in colour- for example, mercuric oleate with ung. potassii iodidi is blue on mixing, but becomes brown quickly, and in a few days it is yellowish white, owing to a series of chemical changes which finally fix the oleic acid as potassium oleate (soft soap). The following are also interesting:

No. I. when dispensed with white soft paraffin (bleached with acid, probably) as the basis for the oleate ointments became green in colour, but did not change with the unbleached paraffin. Copper oleate is easily reduced on heating with certain substances. This was found to be the case with No. II. when the oleate was warmed with 2 drachms of lanoline, but not so when it was melted with olive oil on a water-bath, and the lanoline added when nearly cold.

Percentage questions in respect to the oleates sometimes give rise to divergence of opinion. Thus in a prescription (1897) 'oleat. zinci (5 per cent.) occurred, and the dispensers in the pharmacy suggested that (1) 12 grains of zinci oleat. pulv. should be used or (2) 2 drachms of zinci oleat. B.P., 1885, and the same of oleic acid. At that time the oleate of the British Pharmacopoeia contained 10 per cent, of zinc oxide, and there should have been little hesitation in concluding that the pre-scriber meant a similar preparation containing 5 per cent, of oxide. This oxide basis of calculation no longer obtains since the pharmacopoeial preparations are made by interaction of hard soap and soluble metallic salts. Normal oleate of mercury (to which the B.P. oleated mercury approximates) contains the equivalent of 28.4 per cent, of mercuric oxide, and normal zinc oleate the equivalent of 12.9 per cent of zinc oxide.