ART. V.-Account of some Experiments, made with the view of ascertaining the different substances from which Iodine can be procured. By ANDREW FYFE, M. D., Lecturer on Chemistry. Communicated by the Author.

SIR HUMPHRY DAVY, in one of his early papers on Iodine,

published in the Philosophical Transactions for 1814, mentions, that he had procured this substance from the

Fucus cartilagineus.

membranaceus.

rubens.

Fucus filiformis.

Ulva pavonia.

linza.

He did not, however, obtain it from the alkaline matter manufactured at Sicily, Spain, and the Roman States, nor did coral and the ashes of the sponge seem to contain it.

Shortly after the publication of this paper, I commenced a series of experiments, to ascertain the different substances from which iodine could be obtained.

An account of these was read before the Royal Medical Society of this place, in the winter of 1815. Since then I have had several opportunities of subjecting other substances to analysis, with the view of ascertaining if they would yield iodine.

I may here remark, that at the time when most of these experiments were made, it was not known that starch proved a delicate test of the presence of iodine. I had therefore recourse to that of silver, as pointed out by Sir H. Davy, when the vapour of iodine did not appear, on the addition of sulphuric acid to the saline substance.

The first object in these experiments, was to ascertain the different marine plants from which iodine could be obtained. For this purpose I procured quantities of all the common kinds of sea-weed growing on the shores of Leith. These were dried by a gentle heat, and then burned, either in a large crucible, or in a chaffer; the temperature never being so high as to cause the fusion of the substances. The product of the combustion was then dissolved in water, and the solution was evaporated to dryness. Sulphuric acid was added to the residue in a glass tube,

2

and heat was applied, by which means the iodine, when present, was driven off in vapour. In those cases in which iodine did not appear by the above method, recourse was had to the more delicate test of the presence of this substance.

In this way I procured iodine from the residue of the combustion of the Fucus nodosus, the Fucus serratus, the Fucus palmatus, and the Fucus digitatus; the last of which seemed to afford it in greatest quantity, both from the leaf and stem.

I likewise obtained it from the ashes of the Ulva umbilicalis, and of a species of Conferva. I repeatedly attempted, but without success, to procure it from the Fucus vesiculosus, the ashes o which did not yield the vapour of iodine, on the addition of sulphuric acid, nor did the more delicate test indicate the presence of their substance in their solution. This confirms an experiment of Professor John, in which he failed in obtaining iodine from the Fucus vesiculosus. Dr Thomson likewise mentions, that a foreign chemist did not succeed in procuring it from the above plant +.

I next endeavoured to procure iodine from plants growing near the sea, not belonging to the class Cryptogamia. With this view the Plantago maritima, and Arenaria peploides, were subjected to the usual trials, but without success. I also failed in my attempts to obtain it from the ashes of the Salsola Kali. I was led to expect this, as I did not succeed in procuring iodine from barilla, the product of the combustion of different species of Salsola and Salicornia.

From the above experiments, I concluded that iodine was contained only in the plants of the class Cryptogamia. I was naturally led to examine, if all the plants of this class afforded this substance.

For this purpose I procured several of the fresh water cryptogamous plants, and subjected them, after incineration, to the action of sulphuric acid; but no iodine was given off. I likewise attempted to obtain it from the Agaricus campestris, and a Boletus growing near the sea, from the filices (Polypodium filix and aculeatum), from the musci, and from several species of

• Vid. Annals of Philosophy, November 1815.

+ Ibid. January 1816.

lichens, but without success. It seemed, therefore, that iodine was confined not only to the class Cryptogamia, but to the ma rine productions of this class.

The next object was, to ascertain if the marine animals of the lower orders could be made to yield iodine. For this purpose, the residue of the incineration of oysters was dissolved in water; the solution was evaporated to dryness, and sulphuric acid was added, but without any appearance of iodine. Coral was likewise subjected to a similar trial, and with the same result. I however succeeded in procuring it from the common sponge of the shops, after burning it, and treating it in the usual way *.

As from these experiments, it appeared that iodine was afforded only by marine productions, it was of consequence to ascertain if it could be procured from sea-water itself. With this view, I subjected the residue of the evaporation of sea-water, to various trials.

The common method of procuring muriatic acid from the saline matter of sea-water, by the addition of sulphuric acid, convinced me, that if this substance contained iodine, it could not in this way be got from it. I was therefore obliged to have recourse to other means. When sea-water is subjected to galvanism in a gold cup, a small quantity of a black powder is formed; this, it is supposed by Sir H. Davy, might be a compound of iodine and gold. To ascertain if this was the case, a quantity of sea-water concentrated by evaporation, was put into a silver vessel, attached to one end of a galvanic battery; a gold wire from the other end, was introduced into the fluid. The silver in a short time acquired a dark coating, and a minute portion of a black powder was formed. This was subjected to the action of fused potassa, and then to sulphuric acid, but without any appearance of iodine.

During the preparation of kelp, from which iodine is procured, the vegetable matter is subjected to a high temperature. Conceiving that, perhaps, the iodine might be a product of the combustion, some of the residue of the evaporation of sea-water

In the experiments with sponge, the vapour of iodine was given off copiously, by the addition of sulphuric acid to the ashes. I repeated these experiments several times, as they were at variance with those of Sir H. Davy, Phil. Trans, 1815.

was mixed with charcoal in powder, and a high heat applied to it. When cold, the mixture was treated with sulphuric acid, but without obtaining any iodine.

The saline matter of sea-water was subjected to various other trials, but uniformly with the same result.

In the experiments on the substances mentioned, from which iodine was procured, and also, as I have said, in the preparation of kelp, the bodies are subjected to a high temperature,—are we to infer from this, that the iodine is a product of the combustion?

To determine this, a quantity of the Fucus serratus was infused in water for some hours. On evaporating the solution, a mass of a syrupy consistence was obtained. When this was subjected to the action of sulphuric acid, with the aid of heat, iodine in vapour appeared. The stem of the Fucus digitatus, treated in the same way, afforded iodine. It is remarkable, however, that the infusion of sponge did not in this way yield iodine, though the sponge which had been kept in water for some time, afforded it after being burned and acted on by sulphuric acid.

From the above, we may conclude, as far as these experiments go,

1. That iodine is not contained in sea-water.

2. That it is confined alone to marine productions.

3. That the iodine contained in kelp, is not a product of the combustion.

4. That the substances which afford iodine, belong to the class Cryptogamia, unless, with some naturalists, we consider Sponge as belonging to the animal world, In the classification of Linnæus, however, the Fuci, Ulvæ, and Confervæ, from which I have procured iodine, belong to the class Cryptogamia, subdivision, Algæ aquatica. Along with these, Linnæus was inclined to place the sponge, though he was doubtful of the correctness of this arrangement. If, then, we adopt the opinion of Linnæus, we must conclude, that iodine is confined to the vegetable world; if we incline to the former opinion, iodine must be considered a product likewise of the animal kingdom.

May not the fact, that sponge contains iodine, be an argument in favour of the opinion of Linnæus, that this substance,

properly belongs to the vegetable world, class Cryptogamia, from the plants of which iodine is obtained.

5. It appears that the iodine contained in sponge, is in a different state of combination from what it is in the other substances, as in the former it is not soluble in water, while it is so in the latter.

ART. VI.—On the preparation of Opium in Great Britain. By JOHN YOUNG, Fellow of the Royal College of Surgeons, Edinburgh. Communicated by the Author.

THE natural history of Opium, and the manner of collecting

and preparing it in the East Indies and in Persia, has been fully detailed by Dr Samuel Crump, in his Inquiry into the Nature and Properties of Opium. He examined the different accounts related by authors, from Dioscorides, Pliny, Kæmpfer, and many others, till the year 1792, when his very interesting work was completed.

The preparation of opium in Britain has long been a desideratum. Premiums have been offered by the Society of Arts, and more recently by the Caledonian Horticultural Society. Specimens of British opium have been produced, and proved to be in no degree inferior to the best foreign opium: But it has not yet been ascertained that this valuable drug can be cultivated in Britain with profit to the grower.

The few experiments which have been made, were conducted according to the eastern mode. But the temperature, winds and rain of this climate, have hitherto been justly-considered as insuperable obstacles. Of these the temperature may be held as the least objectionable, for the large White Poppy (Papaver somniferum of Linnæus) from which foreign opium is obtained, comes to maturity in this climate. But it is further objected, that the high winds beat down the plants, and the rains wash off the opium, before it can be collected, when the eastern mode of gathering it is practised. It has therefore been proposed to cultivate the garden poppy of this country, because it is not so liable to be damaged by wind as the large white poppy.