We are glad, in conclusion, to be able to say that there are few passages in the volumes before us so liable to objection as that which we have last produced; that the translation is in general respectably executed, rarely falling into great errors, and sometimes displaying considerable vigour and beauty; and that those persons of literary curiosity, who cannot peruse the tragedies of Alfieri in the Italian, will deny themselves a gratification, if they do not apply to the version of Mr. Lloyd.

ART. XVI.-Memoire sur l'Iode. Par M. Gay-Lussac; lu a l'Institut Royal, le 1er Aout, 1814.

THE discovery of a new simple supporter of combustion, capable, like oxygen, of combining with almost all the combustible bodies, and of forming various acids and genera of salts hitherto unknown, constitutes a very important addition to the science of chemistry, and must have attracted the particular attention of all those who are interested in chemical pursuits. We conceive, therefore, that we shall perform a very acceptable task to our English readers, if we lay before them a clear account of all the facts hitherto ascertained respecting iodine. The treatise which we have placed at the head of this article is by far the fullest that has been published on the subject. But several facts of importance have also been ascertained by Sir Humphry Davy, M. Vauquelin, MM. Colin and Gaultier de Claubry, Dr. Wollaston, and some others. We shall take advantage of the contributions of all these chemists, and endeavour to steer clear of the hypotheses in which some of them have involved themselves. For in chemistry, and indeed in all other sciences, the facts constitute the important department. Hypotheses claim a very subordinate consideration, and indeed are of value merely as they serve to connect the facts already known, or lead to the performance of new experiments.

Iodine was accidentally discovered about three years ago by M. Courtois, a saltpetre manufacturer at Paris. This gentleman thought of employing kelp in his manufactory, and accordingly subjected it to a course of experiments. He observed the metallic vessels in which the solutions of kelp were evaporated very much corroded. This observation led him to make farther experiments, the result of which was the discovery of iodine. He concealed his discovery for some time, doubtless with the intention of investigating the properties of this new substance, and

he actually made some progress in the investigation. But finding that the cares of his manufactory would not allow him the leisure requisite for such an investigation, he communicated the secret to M. Clement, presented him with a quantity of iodine, and requested him to determine its nature. M. Člement accordingly made a good number of experiments upon the subject, the result of which was communicated to the French Institute. about the end of the year 1813, and afterwards published in the Annales de Chimie. But want of leisure likewise prevented this gentleman from fully performing the task which he had undertaken. He therefore presented a quantity of iodine to M. GayLussac, who is the most active, and one of the most sagacious and skilful chemists in France. He undertook the investigation with alacrity, and speedily determining iodine to be a new and an undecompounded substance, he read a notice to the Institute on the subject, and afterwards published the treatise which stands at the head of this article, which contains the result of all his researches on the subject.

Meanwhile M. Ampere having presented Sir H. Davy, who was then in Paris, with a quantity of iodine, he subjected it likewise to experiment, and drew similar conclusions with those of Gay-Lussac. He published a paper on the subject in the Philosophical Transactions for 1814, and has since prosecuted his investigation in several other papers published in subsequent volumes of the same work. Vauquelin's paper on iodine was published in the Annales de Chimie for May and June, 1814, and a paper by Colin and Gaultier de Claubry, on the combinations of iodine and vegetable substances, appeared in the same volume (vol. 90) of that work. To finish the history of the researches hitherto published on iodine, we have only to mention that Dr. Wollaston has ascertained the figure of its crystals, and that Stromeyer has pointed out a re-agent capable of detecting uncombined iodine, though constituting only 50.000 of the liquid in which it is held in solution. We are aware, indeed, that several other chemists have made experiments on this substance, but as they have not yet thought fit to lay their labours before the public, we cannot avail ourselves of the facts which they have ascertained.

Iodine has hitherto been obtained only from kelp, a kind of impure saline substance mixed with much earth, which is prepared in great quantities on the coasts of Great Britain and Ireland by burning the fucus which is cast ashore in such abundance by the sea. It is prepared likewise on the north coast of France, and in that country is known by the name of varec. It appears that the French kelp contains a much greater proportion of iodine than the British. To what this difference is to be

ascribed is not known at present. The method followed by M. Courtois and the French chemists in preparing iodine has not been very particularly described; but the mode originally practised in this country by Dr. Wollaston, and obviously suggested by M. Clement's paper on iodine, is as follows:-the kelp is boiled or steeped in hot water till every thing soluble is taken up: this saline liquor is separated from the insoluble portion of the kelp by the filter, and concentrated by evaporation till all the salts which it is disposed to yield have been deposited. The residual liquid is now to be mixed with a quantity of sulphuric acid sufficient to render it very distinctly acid, and the mixture, after being boiled for some time in an open vessel, is to be filtered through wool. By these means we get rid of a quantity of muriatic acid and of sulphur; both of which, especially the latter, are injurious to the separation of the iodine. Mix the filtered liquid with a quantity of black oxide of manganese in powder, equal in weight to the sulphuric acid originally added to it. Put the mixture into a glass flask, and expose it to heat. A violet-coloured vapour speedily arises from it, which must be received into a glass vessel, or tube, placed over the mouth of the flask. In this vessel it speedily condenses, and constitutes the iodine.

It was from the violet colour of its vapour that our new substance obtained the name of iodine. Gay-Lussac gave it the appellation of ione from ov, the violet. But Sir Humphry Davy conceiving that this term, in consequence of its derivatives ionic and ionian, would lead to ambiguity in our language, suggested the term iodine from wons, violet-coloured; and this term has been generally adopted. Indeed it is preferable to iode, because it is more analogous to oxygen and chlorine, the names of the other two supporters of combustion at present known.

The existence of iodine in kelp naturally supposes its existence in the fuci, by the combustion of which the kelp is obtained. Accordingly Sir Humphry Davy found traces of it in the following sea plants, which were collected on the coast of the Medi

terranean.

Fucus cartilagineus,
membranaceus,
rubens,

Fucus filamentosus,
Ulva pavonia,
Îinza.

But he could discover no traces of it in the ashes of coralines

and sponges.

The late Mr. Smithson Tennant made many attempts to determine whether iodine exists in sea water; and some time before his death he announced that he had discovered distinct traces of it in that liquid; but we are ignorant of the method

which he followed in order to determine the point. It was, however, reasonable to expect, a priori, that it should constitute a constituent of sea water, otherwise it is difficult to conceive how it should make its way into the fuci which derive all their nourishment from that liquid.

1. Iodine, obtained by the process described above, is a solid substance of a blueish white colour and metallic lustre, so as to bear a considerable resemblance to plumbago. It is still more like galena; but perhaps approaches most nearly to the appearance of the crystallized black oxide of manganese. It is so soft that the particles of it may be easily squeezed together between the fingers, bearing, in this respect, a considerable resemblance to an amalgam of mercury.

It has a peculiar smell, which has been compared to that of chlorine, only it is said to be much weaker. But to us it does not convey any such resmblance. The smell seems quite peculiar, and cannot be compared to any other with which we are acquainted.

Iodine is very volatile. If it be left in the open air it speedily disappears, and perfumes the apartment with its peculiar odour. When heated to 225° it melts, and, under the common pressure of the atmosphere, it is volatilized into a violet vapour at the temperature of 350°. It may, however, be distilled over along with the vapour of water.

Iodine crystallizes into rhomboidal octahedrons as was first ascertained by Dr. Wollaston. His method was to put a little iodine into a dry phial, and to set this phial on its side near a common fire. The iodine gradually volatilized and assumed the form sometimes of rhomboidal plates, sometimes of octahedrons. The axes of these octahedrons are to each other, as nearly as can be estimated, as the numbers 2, 3, 4.

Water dissolves about one seven thousandth part of its weight of iodine and acquires an orange yellow colour. Alcohol and ether dissolve it in considerable quantities. These solutions are reddish brown. Water precipitates the iodine from the alcohol in small crystals, which appear at first reddish, but gradually assume the natural colour of iodine.

Iodine has an acrid taste notwithstanding its little solubility in water. From the experiments of M. Orfila we learn, that when taken internally it is poisonous. He swallowed six grains of it. The consequence was a most horrible taste, salivation, epigastralgia, colic, nausea, and violent vomiting. When given to dogs in the quantity of 72 grains or more it generally produces speedy vomiting, by which means it is thrown out of the system and the animal saved. But if vomiting does not take place, or if it be prevented by tying the oesophagus, death ensues in the course

of a few days, without being preceded by any particular symptoms.

Iodine stains the fingers of a deep brown; but the stain very speedily disappears. The specific gravity of this substance, according to Gay-Lussac, is 4.948 at the temperature of 62°. But Clement found it only 4, and the writer of this article found the specific gravity of iodine in pretty large crystals only 3.791. There seems reason therefore to doubt the accuracy of the number given by Gay-Lussac.

Iodine is a supporter of combustion; but a much more imperfect one than any of the other supporters previously known. Potassium, when placed in contact with it, or surrounded by its vapour, burns with a pale blue flame. Phosphorus rapidly combines with it, and much heat is evolved. According to Vauquelin light also appears. But we were not able to observe any such evolution of light in our experiments.

As all attempts to decompose iodine have failed, we must consider it as a simple substance. As it unites, like oxygen, with combustible bodies, and as during this union combustion in certain cases takes place, we must consider it as a supporter of combustion. So that the supporters of combustion at present known are three in number; namely oxygen, chlorine, and iodine. And if fluorine, which there is the strongest reason for considering as a supporter likewise, be ever obtained in a separate state, we shall in that case be acquainted with no fewer than four of these bodies. Let us now consider the compounds which iodine forms with the simple combustibles.

2. The compounds which oxygen forms with the simple combustibles have received the name of oxides, those which chlorine forms are called chlorides. Analogy leads us to give the name of iodides to the compounds which iodine forms with the same bodies. This name appears to us better than the French term iode; we shall therefore adopt it in preference. The simple combustibles have been divided into two classes; namely, simple combustibles proper, and metals. It will be convenient to take these two classes separately.

I. The simple combustibles proper at present known are phosphorus, sulphur, carbon, boron, silicon, and hydrogen, to which we must add azote, though it is not strictly speaking combustible; but in other respects it resembles the other bodies of this class. Of these seven bodies there is one with which iodine does not seem capable of uniting; namely, carbon. Its action on boron and silicon has not hitherto been tried So that there remains four bodies, phosphorus, sulphur, hydrogen, and azote, with which its combinations have been ascertained.

(1.) Iodide of phosphorus. If iodine be put into a glass tube