416
DYEING AND CALICO PRINTING.
yellow, and it emits an aromatic yet nauseous odour. The aloes contains—A yellow crystalline principle, soluble in cold water, and named aloin ; aresinous-looking substance, soluble in boiling water, and called ciloetin . Thefirst-named substance, also known as aloes bitter, is best obtained by ex-hausting Barbados aloes with cold water, after having previously mixed itwith sand, so as to prevent it from caking together. The solution yields, onevaporation to a syrupy consistence, and after standing for a few weeks, acrystalline deposit. The other varieties of aloes do not yield, when treatedas described, an aqueous extract of sufficient purity to obtain therefrom aloinin a crystalline state. The latter substance has the following properties :—Itforms prismatic crystals, tasting at first sweetish, but with a very bitter afterflavour ; sparingly soluble in cold water and cold alcohol, more readily in thesefluids when hot; neutral to test-paper; solutions bright yellow, becomingorange upon the addition of alkalies ; formula, according to Dr. Stenhouse,
C17H18O7.
Aloetin, or aloes resin, is viewed by Winkler as an acid, and by M. Bley asa mixture of two acids : it is insoluble in cold, but readily soluble in hot,water.
According to M. Ulex, commercial aloes consists, in 100 parts, of—Aloin,6g'2 ; aloetin, 25^6; albumen, 5*2. Dr. Kossmann* found that Cape aloescontains chiefly two substances, one of which is soluble in water, and theother insoluble therein, while both, on being treated with very dilute boilingsulphuric acid, are split up into glucose and several resinous substances,which aCt as acids. He finds that the aloetic principle is very readilyoxidisable, especially so in the presence of alkalies. The composition of thesoluble portion of the aloes is Ci 7 H220 io , and by being split up by sulphuricacid it yields aloeretic acid, being a resinous matter, formula C15H16O7, andaloeretin, CX5H24O20, which the above-named author considers as a product ofthe oxidation of aloeretic acid.
The aloin of Stenhouse .is the substance which is primitively present in thelactiferous vessels and cells of the Aloe spicata , and is originally a crystallineand almost colourless substance, but by the aCtion of air, water, and heat,becomes brown and amorphous.f This substance, insoluble in water, has,according to Dr. Kossmann, the composition C51H60O27, and on being treatedwith boiling dilute sulphuric acid it yields glucose and aloeresinic acid,C^HjgOo. The aloin as originally present in the juice of the plant, 3 Ci 7 Hi 80 7 ,yields, by hydratation and oxidation, products insoluble in water, and otherssoluble :—
3C17H18O7 + O3+ 6H 2 0 = 3^i7^220io ; 3C17H18O7+O3+3H2O — C5iH(x>027*^Soluble aloin. Insoluble aloin.
When treated with nitric acid, aloin yields several nitrated coloured com-pounds, and in the first place aloetic acid—prepared by heating, upon a water-bath, 1 part of aloes of commerce with 8 parts of nitric acid (sp. gr. 1*31): thevessel containing the mixture is withdrawn from the ‘water-bath as soon as
* “ Journal dePharmacie et de Chimie,” September, 1861. “Repertoire de Chimie Pure,”vol. v., 1863, p. 530.
t Our readers may be reminded that the ornamental plant commonly called aloe by nursery-men is not an aloe, but an Agave, and entirely different from the aloe here spoken of.