Coal Tar and Salicylic Acid Ointment

Coal Tar and Salicylic Acid Ointment contains 2% w/v of each of Coal Tar and Salicylic Acid in a suitable emulsifying basis.

The following formula and directions apply.

Coal Tar	20 g
Polysorbate 80	40 g
Salicylic Acid	20 g
Emulsifying Wax	114 g
White Soft Paraffin	190 g
Coconut Oil	540 g
Liquid Paraffin	76 g

Disperse the Coal Tar in the Polysorbate 80, incorporate the Salicylic Acid and mix with the previously melted Emulsifying Wax. Separately, melt the White Soft Paraffin and the Coconut Oil, incorporate the Liquid Paraffin warmed to the same temperature and add, with stirring, the resulting solution to the Coal Tar dispersion. Mix thoroughly and stir until cold.

The ointment complies with the requirements stated under Topical Semi-solid Preparations and with the following requirements.

1.90 to 2.10% w/w.

Disperse 2 g of the ointment in 20 mL of water with the aid of gentle heat, cool and filter. The filtrate yields reaction A characteristic of salicylates, Appendix VI.

To 2 g add 50 mL of water, warm until melted, cool and decant the supernatant liquid through moistened absorbent cotton. Repeat the operation with a further three 50 mL quantities of water. Dilute the combined aqueous extracts to 250 mL with water, filter and dilute 10 mL of the filtrate to 50 mL with iron(iii) nitrate solution. Filter if necessary and measure the absorbance of the resulting solution at the maximum at 530 nm, Appendix II B, using in the reference cell a solution prepared by diluting 10 mL of the filtered extract to 50 mL with water. Calculate the content of C₇H₆O₃ from the absorbance of the solution obtained by diluting 10 mL of a 0.016% w/v solution of salicylic acid to 50 mL with iron(iii) nitrate solution, filtering if necessary, and using water in the reference cell.