I endeavored to obtain aloine by operating on considerable quantities of Barbadoes, Cape and Socotrine aloes. These were macerated in cold water, and the aqueous solutions obtained were concentrated to the state of thin extracts on the water-bath. I was quite unsuccessful in every instance. The impurities contained in the extracts in these different kinds of aloes appear, when in contact with the oxygen of the air, to act upon the aloine so as effectually to prevent it from crystallizing. Aloine can only, therefore, be obtained in a crystalline state by {183} concentrating the cold aqueous solution of aloes in vacuo; though, after the aloine has once been crystallized, and it is freed from the presence of those impurities which appear to act so injuriously upon it, the aloine may be quite readily crystallized out of its aqueous solutions in the open air.
Though aloine has as yet only been obtained from Barbadoes aloes, I have scarcely any doubt that it also exists both in Cape and Socotrine aloes. The amount of aloine in Cape aloes, is, however, in all probability, much smaller than in either of the other two species; for Cape aloes is well known to be a much feebler cathartic, and to contain a mass of impurities. In corroboration of this opinion, I would refer to the fact already mentioned in a previous part of this paper, viz. that when aloine is digested with nitric acid, it is converted into Dr. Schunck’s chrysammic acid. Now it has been satisfactorily ascertained that all the three species of aloes yield chrysammic acid, of which in fact they are the only known sources. Cape aloes, as might have been expected, yields by far the smallest amount of chrysammic acid together with much oxalic and some nitro-picric acids. There appears, therefore, great reason to believe that all the three kinds of aloes contain aloine.
Since the above was written, I have learned from Mr. Smith that he has not succeeded in obtaining crystallized aloine from either Cape or Socotrine aloes. Mr. Smith does not doubt that both of these species of aloes also contain aloine, though, most probably contaminated with so much resin, or some other substances, as prevents it from crystallizing. What tends to confirm Mr. Smith in this opinion is the observation he has made, that when the crude crystals of aloine are allowed to remain in contact with the mother liquor of the Barbadoes aloes, they disappear and become uncrystallizable. I have also observed a similar occurrence in the mother-liquors of tolerably pure aloine. These become always darker and darker; so that if we continue to dissolve new quantities of aloine in them, at length scarcely any of it crystallizes out, and the whole becomes changed into a dark-colored magma. {184}
In the year 1846, M. E. Robiquet published an account of an examination he had made of Socotrine aloes. By treating the concentrated aqueous solution of this species of aloes with basic acetate of lead, he obtained a brownish yellow precipitate, which was collected on a filter and washed with hot water. On decomposing this lead compound with sulphuretted hydrogen and evaporating the solution to dryness, he obtained an almost colorless varnish, consisting of a scaly mass, which was not in the least degree crystalline. M. E. Robiquet subjected his substance, which he called aloetine, to analysis, and obtained the following result:—
| 8 C = | 27.7 per cent. |
| 14 H = | 10.8 per cent. |
| 10 O = | 61.5 per cent. |
| 100.0 |
It is plain, therefore, that M. E. Robiquet’s aloetine, if it really is a definite organic principle, which I very much question, is certainly a very different substance from the aloine which has formed the subject of the present notice.—London and Edinburgh Philosophical Magazine.
ON HENRY’S MAGNESIA. BY DR. MOHR.
In England, under this name is sold a calcined magnesia, at a very high price, which is not to be obtained in any other way. Many English travelers, as well as most of their countrymen, believe that they possess a very large knowledge of medicines, because such things as blue pills, calomel, sweet spirits of nitre, and laudanum they administer without medical advice, and {185} bring this magnesia with them to our shops when they wish a recipe to be dispensed, which contains calcined magnesia as one of the ingredients. By such opportunities, I became acquainted with the purity and beauty of this preparation, and its peculiar silky gloss and whiteness. With a view to discover its method of preparation, I made the following research:—
By heating to redness the ordinary carbonate of magnesia, it is not to be obtained. The ordinary magnesia of commerce, which produces by a red heat a fine calcined magnesia, I exposed in a crucible, to a strong white heat. It solidified, and was of a yellow color, and had become so hard that it was only with the greatest labor that it could be powdered and sifted. Prepared in this way, it cannot be used. I now prepared some carbonate of magnesia, observing that Henry’s was very dense, without reference to that result, which was very fine, by precipitation in the heat. The process by which the flocculent magnesia of commerce is obtained, is not explained in any chemical works. Pure sulphate of magnesia, free from iron, was dissolved in distilled water, and a solution of carbonate of soda added to it as long as anything was precipitated by a boiling heat. The ebullition was continued until the mixture ceased to evolve carbonic acid, and set aside for decantation. When decanted, fresh distilled water was added to the precipitate, and the whole again boiled, and afterwards placed on a filter and washed with hot distilled water, until the liquid passing from the filter gave no trace of sulphuric acid. The precipitate, when pressed and dried, was very white and dense. It was exposed to an intense white heat in a closely-covered Hessian crucible for one hour. When the crucible was opened, I found a beautifully white magnesia, finely granulated. Where it had come in contact with the crucible, it had acquired a yellow color, from the peroxide of iron contained in the crucible. The yellow portion alone adhered firmly to the crucible and the rest was perfectly white, and readily removed. In acids, this magnesia was with difficulty dissolved, although ultimately completely soluble therein. By a repetition of this {186} process, an identical result was obtained. The magnesia thus produced in small lumps exhibited by transmitted light a slight rosy tint, and by reflected light, a very white color. In these respects, it agrees perfectly with Henry’s. To determine its comparative density, a cubic inch measure was filled with its powder, and weighed. As the results of three trials, it contained respectively 10,74, 11,19, and 11,18 grammes of the powder. Two experiments with Henry’s magnesia gave 7, and 7,2 grammes. Three of the carbonate of magnesia, prepared by heat, gave 12,68, 12,9, and 12,5 grm. One of the ordinary calcined magnesia gave 1,985 grm.; and one of the ordinary carbonate of magnesia, 1,4 grm.