This method applies in the base or a liquid in small amounts.
(i) Solids are finely powdered and
are passed through a sieve (#250, #180, #125).
(ii) The powder is taken on an
ointment slab and triturated with a small amount of the base. A steel spatula
with a long, broad blade is used. Additional quantities of the base are
incorporated and triturated until the medicament is mixed with the base.
(iii) Finally, liquid ingredients
are incorporated. To avoid loss from splashing, a small volume of liquid is
poured into a depression in the ointment and thoroughly incorporated before
more is added in the same way. Splashing is more easily controlled in a mortar
than on a tile.
Examples
(i) Whitfield ointment (Compound benzoic acid ointment B.P.C.)
Benzoic acid, in fine powder - 6
gm
Salicylic acid, in fine powder -
3 gm
Emulsifying ointment - 91 gm
Method: Benzoic acid and
salicylic acid are sieved through No. 180 sieves. They are mixed on the tile
with a small amount of base and levigated until smooth and dilute
gradually.
(ii) Sulphur ointment I.P.
Sublimed sulphur – 10 g
Simple ointment – 90 g
Method: Sublimed sulphur
is sieved through no. 180 sieves. Then sublimed sulphur is triturated with a small
amount of simple ointment. Then the remaining amount of simple ointment is
added and the mixture is levigated until smooth and homogenous mass is
obtained.