ALOES.

417

effervescence sets in, and when this ceases cold water is added, whereby ayellow powder is thrown down, consisting of a mixture of aloetic and chry-sammic acids, which may be separated by utilising the property of the latterof being insoluble in boiling alcohol, or also by first converting the joint acidsinto potassa salts, and making use of the insolubility of the chrysammate ofpotassa in water.

Aloetic acid is an orange-yellow, crystalline, pulverulent, hitter substance,sparingly soluble in cold water, more readily so in boiling water and boilingalcohol. Its solutions in caustic alkalies are red, while it yields with ammoniaa violet solution which contains an amide. The alkaline aloetates are crys-talline and soluble in water, but the other aloetates are insoluble. Theformula of aloetic acid is C 7 H 2 (N 0 2 ) 2 0 .

When aloes is treated with an excess of boiling and concentrated nitric acid,it is converted into chrysammic acid, C 7 H 2 (N 0 2 ) 2 0 2 . According to Dr. Sacc*this acid is prepared for industrial purposes as follows :—8 kilos, of nitric acid(sp. gr. 1-31) are heated on a water-bath, with the addition of 1 kilo, of aloesin lumps : when the effervescence at first ensuing is finished, another kilo, ofnitric acid is added, and the heating is continued as long as any gas is givenoff; the liquid is then poured into cold water; the acid, which separates as aflocculent matter, is washed first by decantation, and next on a filter, until thefiltrate begins to assume a purplish colour: the quantity of chrysammic acidobtained amounts to about 43 grins.: there are also oxalic and picric acidsformed during this reaction.

Chrysammic acid is a crystalline, beautifully golden-yellow substance,almost insoluble in cold water, to which it imparts, however, a fine purplecolour; it is readily soluble in alcohol and ether; the chrysammates aresparingly soluble in water, and when crystalline display a golden-greenish hue.Chrysammic acid explodes if suddenly heated; sulphuric acid decomposes it,causing an abundant evolution of gas and the produdtion of a violet substance,which, by the addition of ammonia, yields an insoluble blue and a similarlycoloured soluble matter. The alkaline sulphides convert chrysammic acid, inpotassic solution, into a blue crystalline compound (hydrochrysamide), inso-luble in water and alcohol. Ammonia forms, with chrysammic acid, twoamides, viz., chrysamide, a crystalline brownish-red substance, with a metallichue, and chrysamidic acid, a deep olive-green matter.

The first attempts to apply industrially the colouring matters contained inaloes, and those which are its produdts of decomposition, were made inFrance, by Boutin in 1840, E. Rohiquet in 1847, an| i Sacc in 1854. Theresults obtained may be summarised as follows :—An aqueous decodtion ofaloe yields, upon cotton, with acetate of alumina as mordant, and followedby steaming, a pale nutty colour; upon wool, a canary-yellow; with pyro-lignite of iron this decodtion gives upon cotton a deep nut-colour, upon woola bright bistre-brown ; with aluminate of soda the decodtion produces uponcotton a very bright nut-colour, and with stannate of soda a bright dust-greycolour. When aloes decodtion and nitric acid or ammonia are mixed, wool isdyed a deep brown ; aloetic acid yields upon wool a full deep brown colour,which becomes brighter by being passed through a very weak solution ofbichloride of tin, and turns deep bistre-brown when passed through a solution

* “ Bulletins do la Soc. de Mulhouse,” vol. xxvi., p. 149 and following.