Coal Tar and Zinc Ointment

Coal Tar and Zinc Ointment contains 30% w/w of Zinc Oxide and 10% w/w of Strong Coal Tar Solution in a suitable hydrophobic basis.

The following formula and directions apply.

Strong Coal Tar Solution	100 g
Zinc Oxide finely sifted	300 g
Yellow Soft Paraffin	600 g

Mix the Zinc Oxide with the Strong Coal Tar Solution, triturate with a portion of the Yellow Soft Paraffin until smooth, gradually incorporate the remainder of the Yellow Soft Paraffin and mix.

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

28.5 to 31.5% w/w.

The residue obtained in the Assay is yellow when hot and white when cool.

Heat 0.5 g of the ointment gently in a porcelain dish over a small flame until the basis is completely volatilised or charred. Increase the heat until all the carbon is removed. Dissolve the residue in 10 mL of 2m acetic acid and add sufficient water to produce 50 mL. To the resulting solution add 50 mg of xylenol orange triturate and sufficient hexamine to produce a violet-pink colour. Add a further 2 g of hexamine and titrate with 0.1m disodium edetate VS until the solution becomes yellow. Each mL of 0.1m disodium edetate VS is equivalent to 8.138 mg of ZnO.