The exactness of the chief facts relative to the solubility in weak alcohol of the active principle of senna set forth by the said chemists, was also remarkably supported by the long practical experience of T. and H. Smith of Edinburgh.[845]
When cathartic acid is boiled with alcohol and hydrochloric acid, it is resolved into sugar and Cathartogenic Acid.
The alcoholic solution from which the cathartates have been separated contains a yellow colouring matter which was called Chrysoretin by Bley and Diesel (1849), but identified as Chrysophan[846] by Martius, Batka and others. Dragendorff and Kubly regard the identity of the two substances as doubtful.
The same alcoholic solution which contains the yellow colouring matter just described, also holds dissolved a sugar which has been named Catharto-mannite. It forms warty crystals, is not susceptible of alcoholic fermentation, and does not reduce alkaline cupric tartrate. The formula assigned to it is C₄₂H₄₄O₃₈.
Senna contains tartaric and oxalic acids with traces of malic acid. The large amount of ash, 9 to 12 per cent., consisting of earthy and alkaline carbonates, also indicates the presence of a considerable quantity of organic acids.
Commerce—Alexandrian Senna, the produce of Nubia and the regions further south, was formerly a monopoly of the Egyptian Government, the enjoyment of which was granted to individuals in return for a stipulated payment: hence it was known in continental trade as Séné de la palte, while the depots were termed paltes and those who farmed the monopoly paltiers.[847] All this has long been abolished, and the trade is now free, the drug being shipped from Alexandria.
Arabian senna is brought into commerce by way of Bombay. The quantity of senna imported thither from the Red Sea and Aden in the year 1871-72 was 4,195 cwt., and the quantity exported during the same period, 2,180 cwt.[848]
Uses—Senna leaves are extensively employed in medicine as a purgative.
Adulteration—The principal contamination to which senna is at present liable arises from the presence of the leaves of Solenostemma Argel Hayne, a plant of the order Asclepiadeæ, 2 to 3 feet high, growing in the arid valleys of Nubia. Whether these leaves are used for the direct purpose of adulteration, or under the notion of improving the drug, or in virtue of some custom or prejudice, is not very evident. It is certain however that druggists have been found who preferred senna that contained a good percentage of argel.
Nectoux, to whom we owe the first exact account of the argel or hárgel plant,[849] describes it as never gathered with the senna by accident or carelessness, but always separately. In fact he saw, both at Esneh and Phile, the original bales of argel as well as those of senna: and at Boulak near Cairo, at the beginning of the present century, the argel used to be regularly mixed with senna in the proportion of one to four.