centre of the one being the heart, and of the other the head); and that there is scarcely any point of the body which this circle does not involve and rest on, since from almost every point ascends impression to the cerebrum by a nerve of sensation, the anterior nervous roots, and the anterior columns of the spinal marrow; and to each returns expression from the cerebellum by the posterior columns, the posterior nervous roots, and the nerves of volition. Nothing perhaps more than this beautiful correspondence between the vital and intellectual systems is calculated to raise the mind to him of whom the wisdom is testified by all that lives, from the most simple to the most complex of beings-from the polyp which can boast no other organ than a stomach, to man who has an intellectual system thus wonderfully complex and beautifully symmetrical.

Having, Sir, been long engaged in dissections of the brain of fishes, amphibia, and birds, in order further to illustrate and establish these important truths, I shall, on their conclusion, be happy to communicate them through the medium of your Journal. But you will excuse my in future not replying to statements so hastily made as those in answering which I have been reluctantly compelled to occupy so much of your present number-statements in which a confident reference is made to a book for a doctrine which that book, on the contrary, most pointedly contradicts; and to the animal body for a structure which has no other foundation than in the writer's mistaking the branches of a nerve for its roots.

I am, Sir, with great respect,

Your most obedient servant,
ALEXANDER WALKER.

ARTICLE VII.

A Memoir on Iodine. By M. Gay-Lussac,

(Continued from vol. v. p. 413.)

Observations on Chlorine.

THE analogy which I have established between chlorine, sul phur, and iodine may serve to throw some light on some of the combinations of chlorine, as I shall endeavour here to show.

M. Thenard and myself were the first persons who showed by a numerous series of experiments, that oxymuriatic acid might be considered as a simple substance, as there was no direct means of showing the presence of oxygen in it. We had even given this hypothesis at full length, in a memoir which we read to the Society of Arcueil, on the 26th of February, 1809; but it appeared so extraordinary, that M. Berthollet prevailed upon us to state it with the greatest reserve. In fact, though Davy has announced in his memoir on oxymuriatic acid, that this hypothesis had been advanced by Scheele, it was entirely new, and it appeared extra

ordinary only because it was in opposition to a manner of thinking fortified by long habit and by many good experiments. It was making a great step towards the knowledge of the real nature of oxymuriatic acid, to have questioned the received opinions respecting the nature of this acid for it is much easier to find a new truth than to detect an old error. And we claim it as our own property, that we first perceived that oxymuriatic acid might be considered as a simple body. Davy, in adopting the conclusion which we had drawn from our experiments, has added nothing to its certainty ; but we must admit that he has illustrated it at great length, and by the influence of his great abilities, has contributed very much to propagate it. I ought to observe, however, that M. Dulong and M. Ampere had adopted it long before Davy, and that I myself had always stated it as the most probable opinion, in the courses of chemistry which I delivered at the Polytechnic School. At present the discovery of iodine appears to have fixed the opinion of the French chemists on the nature of oxymuriatic acid. I shall therefore refrain from all discussion on the subject.

Admitting then that oxymuriatic acid is a simple body, it becomes in the first place necessary to introduce a modification into the proportions of the muriates. But as this does not follow immediately, from oxymuriatic acid being a simple substance, it may be necessary to justify it. Admitting a muriate to be a combination of muriatic acid and an oxide, it is possible that the hydrogen of the acid and the oxygen of the oxide may not form water; but may remain in the salt. I exposed in succession barytes, strontian, lime, and oxide of zinc, to the action of dry hydrochloric gas, in a glass tube, to a temperature approaching to a red heat, and I always obtained a great deal of water. To verify the same fact on potash, I put about a gramme of potassium in a platinum crucible, melted it, and plunged it into a glass vessel filled with hydrochloric gas. When the combination appeared complete, I weighed the crucible exactly, and then poured water on the salt, which occasioned no effervescence. The salt beeng dried in a low temperature, was found not to have increased in weight, nor after being fused was it found to have lost any thing. We ought then to admit it as a certain fact, that the muriates are all changed into chlorurets when melted, or even dried, and some of them even by being crystallized. We may suppose, as we have done for the iodurets, that the chlorurets dissolve in water without undergoing decompo→ sition, and that when we unite hydrochloric acid with an oxide, the hydrogen of the acid and the oxygen of the oxide form water.* Whether this be the case or not, nothing but chlorurets exist at a red heat. It is therefore of these compounds that it is necessary to determine the proportions.

I have found (Mem. d'Arcueil, ii. 168) that 100 parts of silver take 7.6 of oxygen. Berzelius instead of that number gives 7.44. Though it be difficult to say which is most exact, I shall adopt this

* See Note A,

last number, and will admit further with Berzelius, taking the mean of his results that 100 parts of muriatic acid free from water combine with 424.92 oxide of silver. * Now these 424.92 of oxide are composed of 395.50 of silver, and 29.42 of oxygen. And since in the muriate the silver is in the metallic state, we must, in order to have the weight of the chlorine, add that of the oxygen to the weight of acid which we supposed to be combined with the oxide. We shall thus obtain for the composition of chloruret of silver

Thus, having the proportions of the muriates, we must, in order to obtain those of the chlorurets, add to the quantity of muriatic acid that of the oxygen supposed to be combined with the base. According to the preceding ratio, and the composition of muriate of potash, as found by Berzelius, namely:

I have adopted this last proportion, which differs but little from that obtained directly by M. Thenard and myself.

We find likewise from the same data, that the ratio of oxygen to chlorine is that of 10 to 43.99, or in round numbers 10 to 44. It is therefore nearly three times as great as that of oxygen to iodine. If from the ratio of oxygen to iodine and chlorine we seek the density of chlorine, on the supposition that that of iodine is 8.6095, as we found it above; we find that it is 2·427, instead of 2-421, which was deduced from the supposition that the specific gravity of hydrochloric gas is 1.247.

The great analogy which I found between iodine and chlorine ought naturally to lead me to believe that the salts known by the name of hyper-oxymuriates, are analogous to the iodates; that is to say, that they are combinations of the alkali, with an acid composed of oxygen and chlorine.

It is easy to see that on this hypothesis the acid cannot be the gas found by Davy, and called by him euchlorine. Chemists are nearly agreed that 100 parts of hyper-oxymuriate of potash, when

* I found 418.2. Mem. d' Arcueil, ii. 168.

decomposed by heat, give out about 38.88 of oxygen, and that there remain 61·12 of what has been considered as neutral muriate of potash; but which is, in fact, chloruret of potassium. From the proportions given above, the 61.12 contain 28-924 chlorine, and 32-196 potassium. Now this quantity of potassium would take 6.576 of oxygen to convert it into potash. There remain, of consequence, 38.88 6.576 32.304 for the 28-924 of chlorine; hence the acid which I suppose to exist in hyper-oxymuriate of potash must be composed of

and the oxygen will be to the chlorine in a proportion five times greater than that which I have already given. It deserves attention that the proportion in weight of the potassium in the chloruret, ioduret, and sulphuret, is nearly the same as that of the oxygen in the chloric, iodic, and sulphuric acids.

According to Davy euchlorine gas contains one volume of chlorine and half a volume of oxygen; and taking 2-421 for the specific gravity of chlorine, we find that euchlorine is composed by weight of

Chlorine
Oxygen

100
22.79

This last number, multiplied by 5, gives 113.95, and though it differs from 111.68, we may, notwithstanding, conclude, that the acid existing in the hyper-oxymuriates, which I shall henceforth call chloric acid, contains five times as much oxygen as euchlorine gas.

If we dissolve chloruret of potassium (composed of 100 chlorine and 111.31 potassium) in water, and suppose that the water is decomposed, we will have hydro-chlorate of potash, admitting the oxygen to combine with the potassium and the hydrogen with the chlorine. But if we suppose the oxygen to unite with the chlorine, we form exactly euchlorine gas. I consider this gas formed by the combination of two parts in volume of chlorine and one of oxygen, as analogous to the protoxide of azote, which contains two volumes of azote and one of oxygen. Hence I propose to distinguish it by the name of oxide of chlorine. We may likewise distinguish by the names of oxide of sulphur and oxide of iodine, combinations of sulphur and iodine with oxygen, in the same proportions in volume. The first gives by weight about 10 oxygen and 20 sulphur; the second 10 oxygen and 156-21 iodine. I think it very probable that chlorous and iodous acids exist analogous to the sulphurous and nitrous, which ought to be composed of one volume of chlorine or vapour of iodine, and 15 of oxygen.

It appears to me demonstrated from the quantity of oxygen in oxide of chlorine, that this oxide does not exist in the hyperoxymuriates. Davy, however, is of a different opinion, for he

says that "euchlorine produces the phenomena which Chenevix in his paper on oxymuriatic acid ascribes to hyper-oxymuriatic acid?" and that "it is probably combined with the peroxide of potassium in the hyper-oxymuriate of potash." But I shall demonstrate that this is not the case. *

We must admit it as an incontestable principle, established by Berthollet, that an acid put into a saline solution acts on the base of the salt, and separates a portion of it from its acid. This principle holds especially with the strong acids when brought in competition with the weak acids. On the other side, we must recollect, that peroxide of potassium does not combine with sulphuric acid, and that as soon as these two bodies are brought in contact, oxygen is disengaged. Hence, if hyperoxymuriate of potash were produced by the combination of euchlorine with peroxide or potash, there ought to be disengaged oxygen gas, when diluted sulphuric acid is poured into a solution of this salt. Since at least the euchlo rine, a gaseous oxide, whose acid properties, if it has any, are very weak, will be partly separated by the sulphuric acid, and this acid is incapable of dissolving peroxide of potassium. But no oxygen is disengaged, and consequently the potassium is not in the state of peroxide in hyper-oxymuriate of potash. Besides, even supposing potash super-oxygenated in the hyperoxymuriate, it ought to contain five times its usual quantity of oxygen, a conclusion which it would be very difficult to admit. The fact is, that potassium is in the same degree of oxydation in the hyper-oxymuriate as in the sulphate, as I shall now demonstrate, by giving an account of the real acid which forms the fulminating salts of chlorine.

In consequence of the above considerations, I was led to believe, that since sulphate of barytes is insoluble, and barytes is not superoxydated in this salt, if sulphuric acid be put into the hyper-oxymuriate of barytes, it would be easy to see if oxygen be disengaged, and perhaps even to obtain chloric acid. I accordingly prepared a certain quantity of this salt, employing the ingenious process of Mr. Chenevix, and I obtained it easily in fine rhomboidal prisms, quite exempt from muriate. Into a diluted solution of this salt I poured weak sulphuric acid. Though I only added a few drops of acid, not nearly enough to saturate the barytes, the liquid became sensibly acid, and not a bubble of oxygen escaped. By continuing

In a preceding memoir on oxymuriatic acid, Davy appears to doubt the existence of an acid in the hyper-oxymuriates. He expresses himself in this manner. "If we consider with attention the facts concerning the hyper-oxymuriate of potash, we can only consider it as a triple compound of oxymuriatic acid, potassium, and oxygen. We have no sufficient motive to conclude that any particular acid exists in that body, or that it contains a considerable quantity of water. It is perhaps more conformable to chemical analogy, to suppose the great quantity of oxygen to be combined with the potassium, the very great affinity of which for oxygen we know, rather than to consider this quantity of oxygen as in a state of combination with the oxymuriatic acid, which, as far as we know, has no affinity for that substance. And from some experiments, I am induced to believe' that potassium may combine directly with more oxygen than exists in potash.”