Art. LXV.—On a Search for the Poisonous Principle of Brachyglottis repanda and B. rangiora.
[Read before the Wellington Philosophical Society, 11th February, 1882.]
The leaves of Brachyglottis repanda, so well known to be poisonous to horses, etc., I examined some years ago for the purpose of determining the chemical nature of the principle to which this property is referable, but my efforts were unsuccessful, in spite of which I was enabled to report as the result of this investigation that the “poisonous part is not an alkaloid.”
A few weeks ago, however, I was kindly presented by the Hon. Mr. Mantell with a small quantity of a substance which he had observed to exude from a freshly-cut shrub of Brachyglottis rangiora, a variety of the plant distinguished and named by Mr. Buchanan, and stated by him to be a native only of the provincial district of Auckland. This substance proved to be essentially a balsam, that is, a mixture of essential oil and resin, these together amounting to 99.42 per cent.
As in my former experiment, I failed to find anything in it having the character of an alkaloid, although I extracted, by means of warm water, a small quantity of a bitter substance from it, and found a little nitrogenous matter present.
Experimenting with the balsam in a tentative way, I soon found that it gives a very remarkable, indeed I may say an unique, reaction for a balsam with acids generally. In warm hydrochloric acid, for instance, it colours to a purplish red; even at common temperatures, if time be allowed, this comes about. But the most striking effect is produced by heating the balsam with alcohol acidified by any strong acid, a rich deep-blue liquid being thus obtained. Subsequently it was ascertained that the same effect is to be got by using the leaf or the fresh shoots of this plant in place of the balsam; even the old wood can give a feeble reaction of this sort. And it was further ascertained that the variety of this plant which covers many of the hills in the vicinity of Wellington (Brachyglottis repanda) also behaves in this way with acids.
It was considered that the substance giving this reaction is likely to be the poisonous part of the balsam, chromatic reaction being obtainable with a great number of organic poisons. I therefore at once took means to isolate both the oil and resin for separately testing. For this the balsam was put in a retort along with water, and heat applied thereto. The distillate contained an oil which was partly in solution and partly floating upon it; both the clear solution, as separated from the floating oil, and the pure oil, giving the same reaction as the balsam did in the acids and alcohol.
The residue in the retort, however, also gave the same reaction, although the distillation had been continued for eight hours; nor did it appear possible to eliminate from this residue the substance which is colourable in this way. To ascertain, therefore, whether or not this colourable substance is wholly volatile, I evaporated an ethereal solution of the balsam to dryness, and the thin film so obtained I submitted to a temperature of 212° Fahr. for two hours. The residue was not found capable of colouration by acids.
It was established, therefore, that the only part of the balsam which gives this chromatic effect is volatile, and as I was not able to separate any solid matter from this distillate I conclude that it is an essential oil. This oil is, I find, so rapidly changed in contact with air and water at an elevated temperature, that it is best separated from the balsam by dry distillation, out of contact with air as far as possible.
Separated in this way, its taste and other properties are besides best observed. It is then found to be slightly bitter and acid, warm to the mouth, with a fragrant odour; it is feebly soluble in water, readily soluble in alcohol, also in ether. An aqueous solution of it affords no precipitate with mercuro-iodide of potassium, nor yet with mercuric-chloride, but it gives a pale-yellow or white precipitate with the above-named salts successively applied. It also gives a precipitate with tannic acid, but none with alkalies, acids, or bi-chloride of platinum.
With oxalic or tartaric acid, even at a temperature of 212° F., it does not colour; but with all the mineral acids, or even acetic acid, it colours as has been already indicated, and this even at common temperatures. If the oil is, however, first warmed with any free alkali, it then does not become coloured by contact with any acid.
The blue or light purple compound formed out of this oil by acids,* assumes a yellowish colour when alkalized, but reacquires its normal tint when acidified. In contact with warm nitric acid or nascent hydrogen it also loses its blue colour, and in such a way that it appears impossible to restore it.
It has been found to be almost unalterable under ordinary conditions, standing as it does with seeming impunity a temperature of 212° F., but whether it has sufficient permanency to allow of being profitably used in the dye-house, has yet to be ascertained.
The nature of the change which is wrought upon the oil in question while it is acquiring the colour described, I cannot as yet ascertain. All I can yet be certain of is that it then splits into two or more substances. In this respect it resembles digitaline, that poisonous resin of foxglove which
[Footnote] * Both the balsam and this blue-coloured product of it were exhibited.
is coloured green by warm hydrochloric acid, and also to karakine, the crystallizable and most likely the poisonous resin of the karaka berry.* It differs, however, from both these principles in not being a glucoside as I have shown these to be.
The experiments which I have made with this colourable substance upon animals have not given results of a nature so decisive as to warrant me in ascribing to it the poisonous properties of the balsam, but I hope soon to be able to supplement this paper with an account of experiments which will settle this interesting point. Sufficient has, however, I think, been adduced to show that whether or not this colourable matter is the poisonous part of the plant, a very remarkable principle has been found to exist therein, and one which is well worthy of the attention of those who have the leisure and inclination to make organic chemistry their especial study. To coax the labours of these people in this direction, I shall send a sample of the balsam to some chemist of repute in the Mother Country for diffusion at his discretion.
I should state that the resin from which this oily matter has been removed showed no remarkable reaction to chemical tests; it may be divided into two resins by the use of alcohol and ether.
The following tabular statement represents the approximate composition of the balsam:—
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Resin soluble in alcohol||67.42|
|" insoluble in ether and alcohol||.31|
|Water and nitrogenous matter||.57|
In this connection I may observe that the young shoots of all the common shrubs and trees which I have treated in this way with acids, for comparative purposes (some 50), give not a blue-coloured substance, as the Brachyglottis does, but a red-coloured one—Erythrophyll as I conceive, which is the red colouring matter of autumnal leaves.† The singularity of the fact therefore, that the wood, etc., of the Brachyglottis affords, under the circumstances described, a blue substance, is strikingly brought home to us.
[Footnote] * “Trans. N.Z. Inst.,” vol. iv., art. 53.
[Footnote] † The base of this substance is also present in Brachyglottis, but in comparatively small quantity.