This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Cape Aloes. Large quantities of aloes of excellent quality are exported from Mossel Bay to Cape Town in Cape Colony. It is obtained from Aloe ferox, Miller, a species widely distributed in South Africa and often occurring in considerable quantity. The aloe juice is collected in goat-skins covering a hollow in the ground around which the cut leaves are piled; from these it is transferred to tins, and finally boiled down over a naked fire in iron pans. This variety of aloes, which is preferred in Austria and Germany, occurs in masses of a dark reddish brown or nearly black colour, often with a greenish tinge, and breaking with a clean, glassy fracture. Thin splinters are perfectly transparent, of a reddish brown or amber-yellow colour, and exhibit no trace of crystals when examined under the microscope. It belongs therefore to the class of glassy, lucid, or vitreous aloes, and may be easily distinguished from all other glassy aloes by its very distinctive sour odour and by the pale yellow colour of its powder,
Recently the aloe juice has been allowed to undergo slight fermentation and then dried in shallow troughs exposed to the sun's heat. This aloes is known as ' Crown' and also as ' Uganda ' aloes, the latter being a very misleading fancy name; it occurs in bricks or fragments of a yellowish brown colour and bronze-gold fracture; it has the odour of Cape aloes, but is distinctly an hepatic aloes. It is now practically obsolete.
Natal Aloes. The botanical source of this variety of aloes, which is seldom imported, has not yet been definitely ascertained (possibly A. succotrina, Garsault).
Natal aloes is almost always opaque, and has a characteristic dull greenish black or dull brown colour. In odour it closely resembles Cape aloes, and it may therefore be easily distinguished from all other opaque aloes by this character alone. It yields when scraped a pale greyish green or sometimes pale yellowish powder, and when this is mixed with a little sulphuric acid and the vapour of nitric acid blown over it, a deep blue coloration is produced.
These last three characters are so distinctive that Natal aloes is one of the easiest to identify.