Detection of Turmeric in Powdered Rhubarb and Yellow Mustard.
By J. M. MAISCH.
Rhubarb root which has been attacked by insects, or deteriorated in consequence of dampness and heat, is by some dealers sent to the mills and ground together with some sound rhubarb, or, if the color is not sufficiently bright, turmeric is added, and the powdered rhubarb finds its way afterwards into the hands of the unsuspicious as a prime article. The fraud may be detected in a few minutes in the following manner:
A small quantity of the suspected rhubarb is agitated for a minute or two with strong alcohol, and then filtered. Chrysophanic acid being sparingly soluble in this menstruum, the brown yellow color of the filtrate is due to the resinous principles of rhubarb mainly; if adulterated with turmeric, the tincture will be of a brighter yellow shade. A strong solution of borax produces in both tinctures a deep red brown color. If now pure muriatic acid be added in large excess, the tincture of pure rhubarb will instantly assume a light yellow color, while the tincture of the adulterated powder will change merely to a lighter shade of brown red. The test is a very delicate one, and is based on the liberation of boracic acid, which imparts to curcumin a color similar to that produced by alkalies, while all the soluble principles of rhubarb yield pale yellow solutions in acid liquids.
The same test, applied in the same manner, is also applicable to ground mustard seed. The seeds of Sinapis alba yield a powder of a yellow grey color, entirely distinct from the color of yellow mustard met with in the market. Agitated with alcohol and filtered, a turbid solution is obtained, which assumes a bright yellow on the addition of the borax solution, and becomes colorless or whitish again on being supersaturated with muriatic acid. If the mustard be colored with turmeric, the filtrate has a yellow tint, becomes brown red by borax, and retains the color on the addition of muriatic acid. All the so.called yellow mustard of our commerce which I have had occasion to examine, whether ground in England or in the United States, contains turmeric. This practice ought to be discountenanced; for, under the yellow color imparted by curcuma, adulteration of mustard may be carried on to an almost indefinite extent, if strength be supplied by the addition of a little capsicum.