Hydrargyri Oxidum Flavum

The original Pagen-stecher's ointment is made with oxide freshly precipitated from dilute solutions of mercuric chloride and caustic soda, the washed precipitate being dehydrated by washing with alcohol and ether in succession. This is all done in a dark room, even the mixing with the basis- said to be spermaceti ointment, but the acidity of that basis destroys the colour of the oxide (see page 216). Dr. W. H. Martindale (C.&D. 1906,11. 719) mixes the moist precipitate (without alcohol-ether washing) with soft paraffin in the proportion of 10 of paraffin to 1 of yellow oxide (in the precipitate), diluting as required. Mercuric chloride 1 1/4 yields 1 of yellow oxide. Another good basis for the moist precipitate is wool-fat 1 and soft paraffin 8.

Hydrargyri Perchloridum

Small particles of mercuric chloride irritate the skin intensely, so that in compounding into ointment it is advisable to triturate with glycerin (2 minims to each grain) before adding the basis. When prescribed along with potassium iodide in ointment, rub together in a mortar until perfectly smooth, then mix with the basis. In this case it is apparently the intention to have mercuric iodide formed before the basis is added, and in this connection it should be noted that if the ointment does not contain free alkali (potassium carbonate) it liberates iodine on the cotton dressing or on the abraded skin of the patient, causing intense annoyance. The decomposition has even been observed with ung. potassii iodidi containing 1 of mercuric iodide in 3,000 of the ointment.

Ichthyol

The ammonium ichthyol is generally used, and if prescribed with water and fat dissolve the ichthyol in the water, adding to the fat gradually.

Iodine is first rubbed down by itself, then with about its own weight of the fatty excipient. At this point a few drops of rectified spirit should be added, and the rest of the basis then worked in. If any haloid salt, such as iodide of potassium, is to be combined in the ointment, triturate the iodine with the salt and sufficient water to dissolve, then work in the basis.

Iodoform in ointments should be reduced to fine powder and mixed with the cold basis. Heat should not be used. See remarks under Suppositories.

Mercurial Ointments

A series of experiments published in The Chemist and Druggist, 1884, page 18, proved that mercurial ointments may be made with steel knives with out harm, unless an acid or aqueous ingredient be present. The following prescriptions serve as good examples of chemical changes leading to difference in physical appearance on keeping:

No. I. became dark green in colour, a change which suggests formation of black mercurous oxide and yellow mercuric oxide. In No. II. white streaks formed on keeping, probably owing to fatty acids combining with the yellow oxide; spermaceti ointment is in any case a bad basis for eye-ointments, as it irritates on account of the benzoin which it contains. It is customary to prepare it without benzoin for ophthalmic use.