River. Part is exported to London via Singapore, but much reaches the market by way of France. It appears in commerce either as separate tears or in the form of masses composed of tears more or less firmly cemented together by a dark reddish brown, transparent resin.

The tears vary considerably in size, but seldom exceed 5 cm. in length, by 1 cm. in thickness; usually they are much smaller. They are flattened, or sometimes, if large, concavo-convex, this shape being evidently caused by the resin accumulating between the trunk and bark of the tree. They are opaque, brittle, and milky-white internally, but are usually covered with a thin coating of brownish resin, which increases as the tears are kept, being produced from the opaque tear by oxidation.

Block Siam benzoin consists of small tears cemented together by a glassy, reddish-brown, transparent or translucent resin, which gives them a peculiar varnishy appearance. In this case also the proportion of the red, transparent resin increases as the drug is kept until it becomes its most prominent feature.

Both varieties of Siam benzoin are characterised by their agreeable fragrant odour, recalling vanilla; they are almost entirely soluble in alcohol and in ether, yielding only about 2 per cent, of insoluble residue. When quite pure Siam benzoin affords only traces of ash.

Good commercial samples of Siam benzoin should not yield more than 3 per cent, of substances insoluble in alcohol or more than 1 per cent, of ash.

Constituents

The white tears of Siam benzoin are crystalline and consist chiefly of the benzoate of a resin alcohol, lubanol. When warmed "to about 50° the white tears become yellow, red and brown and lose their crystalline character, a change due to oxidation. In addition the drug contains siaresinol benzoate which also is crystalline and an amorphous benzoate which in alkaline solution, readily oxidises.

Further constituents are vanillin and an oily aromatic liquid, probably an ester of benzoic acid. Siam benzoin contains about 39 per cent, of total aromatic acids (about 23 per cent, free and 16 per cent, combined), 36 per cent, being benzoic acid and 3 per cent, cinnamic acid (Cocking and Kettle, 1914). This proportion of cin-namic acid is so small that it cannot be detected by the official test (heating with solution of potassium permanganate).