Acidum Tannicum

This acid should be compounded with fats in the cold, if possible. First triturate the acid lightly in a mortar, then add its own weight of the basis, and continue trituration for three minutes before adding the rest. This is the plan to adopt with most crystalline substances.

Alkaloids

It is commonly said that alkaloids ordered in ointments should be combined as oleates, so that they may be certain of absorption. The remarks made on this subject in dealing with suppositories apply equally to ointments. It is not advisable to add oleic acid unless the ointment is to be used by friction. Castor oil has been recommended for dissolving pure alkaloids either for use in such solution or previous to admixture with another base. In this connection it is well to bear in mind that castor oil and liquid paraffin are not soluble in each other: they appear to be at first sight, but ultimately separate into two layers. Alkaloidal salts, which are readily soluble in water, may be dissolved in the smallest possible quantity of that solvent before being added to the basis, provided the weight of the ointment is not materially increased by the addition.

No. I. is the prescription of the late Mr. Marcus Gunn. It is peculiar in prescribing yellow vaseline, because Mr. Gunn found from experience that white vaseline irritates the eye, which is against the rule 'white vaseline for colourless ointments, yellow for any other.'The ointment was made by triturating the alkaloid with a few grains of the basis and adding the rest. It acted promptly and perfectly. From the ointment No. II. atropine crystallised out on cooling. This alkaloid was therefore mixed with the boric acid, the cocaine dissolved in the vaseline, and the two then incorporated.

Balsam. Tolutan. - An ointment containing 1 ounce of this balsam and 1 ounce of lanoline was compounded by Mr. Forster (Northampton) by dissolving the balsam in 6 drachms of chloroform (by careful heating), squeezing through muslin, and mixing with the lanoline.