This section is from the book "Materia Medica And Therapeutics: An Introduction to the National Treatment of Disease", by John Mitchell Bruce. Also available from Amazon: The pharmacology and therapeutics of the materia medica.
The dried tubercles of Exo-gonium purga. Imported from Mexico.
Characters.-Varying from the size of a nut to that of an orange, ovoid, the larger tubercles frequently incised, covered with a thin brown wrinkled cuticle; presenting, when cut, a yellowish-grey colour, with dark brown concentric circles.
Composition.-Jalap contains 15 to 20 per cent. of the officinal resin, which in turn is composed in part of convolvulin, C31H50Ol6, a colourless, tasteless, odourless body, of gummy appearance. This is the anhydride of convolvulinic acid, into which it can be converted by alkalies. Convolvulin is probably identical with the jalapin of scammony.
Dose.-10 to 30 gr.