Rape oil is the subject of extensive adulteration, principally with the cheaper hemp oil, rosin oil and mineral oils.
These sophistications can be most conveniently detected, first by taste and next by saponification, rosin oil and mineral oil remaining unsaponified, hemp oil giving a greenish soap, while rape oil yields a soap with a yellow tinge.
Linseed oil is subject to various falsifications, chiefly through the addition of cotton-seed, niger-seed and hemp-seed oils; and rosin oil and mineral oils also are not infrequently added.
On a large scale it is treated by destructive distillation for the production of rosin spirit, pinoline and rosin oil.
