| 1868 | 1869 | 1870 | 1871 | 1872 |
| none | 38 cwt. | 646 cwt. | 372 cwt. | 501 cwt. |
Chemical Composition—All kinds of aloes have an odour of the same character and a bitter disagreeable taste. The odour which is often not unpleasant, especially in Socotrine aloes, is due to a volatile oil, which the drug contains only in minute proportion. T. and H. Smith of Edinburgh, who contributed a specimen of it to the Vienna Exhibition of 1873, inform us that they obtained it by subjecting to distillation with water 400 lb. of aloes, which quantity they estimate to have yielded about an ounce. The oil is stated in a letter we have received from them, to be a mobile pale yellow liquid, of sp. gr. 0·863, with a boiling point of 266-271° C.
Pure aloes dissolves easily in spirit of wine with the exception of a few flocculi; it is insoluble in chloroform and bisulphide of carbon, as well as in the so-called petroleum ether, the most volatile portion of American petroleum. The sp. gr. of fine transparent fragments of aloes, dried at 100° C., and weighed in the last named fluid at 16° C., was found by one of us (F.) to be 1·364; showing that aloes is much more ponderous than most of the resins, which seldom have a higher sp. gr. than 1·00 to 1·10. In water aloes dissolves completely only when heated. On cooling, the aqueous solution, whether concentrated or dilute, becomes turbid by the separation of resinous drops, which unite into a brown mass,—the so-called Resin of Aloes.[2573] The clear solution, after separation of this substance, has a slightly acid reaction; it is coloured dark brown by alkalis, black by ferric chloride, and is precipitated yellowish-grey by neutral lead acetate. Cold water dissolves about half its weight of aloes, forming an acid liquid which exhibits similar reactions. The solution of aloes in potash or ammonia is precipitated by acids, but not by water.
The most interesting constituents of aloes are the substances known as Aloïn. This name was originally applied to an aloïn which, as it appears to be found exclusively in Barbados aloes, is now termed Barbaloïn, in order to distinguish it from allied substances occurring in Natal and Socotrine aloes.
Barbaloïn was discovered by T. and H. Smith of Edinburgh in 1851,[2574] and was described (1851) by Stenhouse. From good qualities of the drug it can be obtained, according to Tilden,[2575] as a crystalline mass, to the extent of 20 to 25 per cent., but in others it appears to occur partly amorphous or in a chemically altered state. Barbaloïn is a neutral substance, crystallizing in tufts of small yellow prisms. These crystals represent hydrated aloïn, and part with one molecule of water (=2·69 per cent.) by desiccation in vacuo, or by the prolonged heat of a water-bath. Barbaloïn, C₃₄H₃₆O₁₄ + H₂O, dissolves sparingly in water or alcohol but very freely if either liquid be even slightly warmed; it is insoluble in ether.
The solutions alter quickly if made a little alkaline, but if neutral or slightly acid, are by no means very prone to decomposition. By oxidation with nitric acid, barbaloïn yields, as Tilden (1872) has shown, about a third of its weight of chrysammic acid, besides aloëtic, oxalic, and picric acids. It easily combines with bromine to form yellow needles of Bromaloïn, C₃₄H₃₀Br₆O₁₄; Chloraloïn, C₃₄H₃₀Cl₆O₁₄ + 6H₂O, crystallizing in prisms, has likewise been obtained.
In examining Natal aloes in 1871, we observed it to contain a distinct crystalline body, much less soluble than the ordinary aloïn of Barbados aloes. We have accordingly named it Nataloïn.
Nataloïn exists naturally in Natal aloes, from which it can be easily prepared in the crude state, if the drug is triturated with an equal weight of alcohol at a temperature not exceeding 48° C. This will dissolve the amorphous portion, from which the crystals should be separated by a filter, and washed with a small quantity of cold spirit. From 16 to 25 per cent. of crude nataloïn in pale yellow crystals may be thus extracted. When purified by crystallization from methylic alcohol or spirit of wine, it forms thin, brittle, rectangular scales, often with one or more of their angles truncated. The formula assigned to nataloïn by Tilden, which is supported by the composition of the acetyl derivative he has succeeded in obtaining, is C₂₅H₂₈O₁₁.
At 15·5° C., 60 parts of alcohol, 35 of methylic alcohol,[2576] 50 of acetic ether, 1236 of ether, and 230 of absolute alcohol, dissolve respectively one part of nataloïn. It is scarcely more soluble in warm than in cold spirit of wine, so that to obtain crystals it is best to allow the solution to evaporate spontaneously. Water hot or cold dissolves it very sparingly. Nataloïn gives off no water when exposed over oil of vitriol, or to a temperature of 100° C. By the action of nitric acid, it affords both oxalic and picric acids, but no chrysammic acid. It appears not to combine with chlorine or bromine, and we have failed in obtaining from it any such body as bromaloïn.
Liquid Socotrine aloes, imported into London about 1852, was noticed by Pereira to abound in minute crystals, which he termed the Aloïn of Socotrine Aloes, and regarded as probably identical with that of Barbados aloes. Some fine dry aloes from Zanzibar of very pale hue, in our possession, is in reality a perfectly crystalline mass.