tween this odour and that which is left after the discharge of ordinary electrical machines, and the fall of the electrical fluid from the atmosphere. He thinks it ought to be attributed to a particular substance extremely subtle, of the same kind as chlorine or fluor, and which, like them, would have a great affinity for oxidable bodies, and which being spread in the air and in the water in a state of combination, would be separated from bodies with which it is combined by the decomposing force of electricity. He proposes to name this new substance ozone.

I must avow, that in repeating carefully the ingenious experiments of M. Schoenbein, to which I added some others, I arrived at a different conclusion to his. I shall not insist on the different objections which his hypothesis appeared to present to me. I shall confine myself to pointing out two of them. The first is, that I do not clearly see with what substance the ozone is found combined in the air and in the water whence electricity disengages it. Is it with hydrogen? But in that case, there ought then to be an excess of hydrogen in the decomposition of the water, and we ought to find hydrogen in the air, which also contains ozone. The second objection is, that M. Schoenbein admits that instantaneous electric discharges, such as from a Leyden jar or from a thunder cloud, have a decomposing virtue. Now, I do not believe that it is thus, and I think that in order to separate oxygen and hydrogen, and consequently ozone, a continuous electric current is necessary. I will add, in fine, that inasmuch as azone has not been isolated, it will be difficult to admit its existence, at least to be able to invoke in its favour proofs so conclusive as those that exist for the existence of fluor.

In repeating the experiments of M. Schoenbein, I have been convinced, as he was, that it is not necesary to seek for the cause of this sulphurous or phosphorous odour in strange substances mixed with the water that we decompose, such as the acids. But I am still at a stand on the idea that I had before the publication of the work of M. Schoenbein, namely, that this odour proceeds from the metal which is used at the pole of the pile in the liquid.

I at first proved, with a very strong pile, the fact of the transportation of very finely divided metallic particles from the + pole to the pole in the air, as a vacuum, in making use as poles of two morsels of spongy platinum very near together, but not in contact, in place of two charcoal points. I have even obtained some traces of the odour in this experiment. I have remarked, that when we decompose water pretty well acidulated, with a very strong current, by means of two wires, or two plates of platinum which have not a very great surface, we see at the end of a certain time, and when the liquid traversed by the current is strongly heated, a deposit of a black powder, which is platinum divided; the platinum appears to be detached from the wire and the plate which is used at the positive pole. I am disposed to believe then, that the current which comes from the positive pole, draws with it extremely attenuated par

ticles of the metal of which the pole is made, which thus remain in suspension in this gas, to which they give by their presence the odour in question. This odour will then be due to very finely divided molecules of a metallic oxide.*

The presence of oxidable bodies ought, as M. Schoenbein has observed, to make this odour disappear, because the immediate result from it is the oxidation of the platinum. The elevation of the temperature of the liquid will likewise produce the same effect, because it reduces the oxide. It is really a remarkable thing, that when the current is very energetic, and it has traversed the liquid long enough to heat it considerably, there is no longer any trace of the odour.

manner

All these results, proved by experiment, agree very well with my hypothesis; but there is one fact which appears to me to be eminently favourable to it. If we make use, for the decomposition of water slightly acidulated, containing for example in volume of sulphuric acid, of a pile of constant force of ten elements, feebly charged, we have no trace of the odour, by taking for the poles two plates or two long wires of platinum. But if, without changing the plate or the wire, we diminish the surface of the wire which forms the positive pole, very much, either by covering it with wax, and thereby not leaving it in immediate contact with the liquid, only at some points, or by enclosing the platinum in a glass tube, in such a that its extremity alone is in contact with the liquid, we then obtain, though the current be rather feeble, since it does not pass the liquid with such facility, an excessively strong odour. Farther, we find when the decomposition has lasted some time, those parts of the platinum by which the current could escape, slightly corroded. Thus it is when the current, being restrained in its passage from the positive pole in the liquid, becomes thereby condensed on some points, and in making its escape it draws along these metallic particles, which, when oxidized, give out the odour in question. With a very strong pile the odour will be manifested in general more easily, because the curreut, being considerable, will meet with resistance in passing through the same conductor which offers no restraint to a current of less intensity; but when even the current is feeble it will produce the odour, provided that its transmission is restrained.

As to the odour which accompanies electric discharges, and the fall of the thunderbolt, it is still more easy to prove that it is due to very finely divided substances, which the electricity has transported with it. The fact of this transport has been proved by the numerous experiments of Priestley, who has shown that the spark taken from the conductor of a machine is charged

• These oxidized metallic particles which are detached from the platinum wire, explain how it is, as we have before seen, that the proportion of oxygen which disappears in the decomposition of water, is always greater than that of hydrogen, especially if the current is strong.

with metallic molecules emanating from the conductor, and which go in the direction of the positive electricity. Fusiniere has likewise shown the existence of this transport by the thunderbolt. The aura, which positive electricity produces when it proceeds from a conductor, is probably only due to the combustion of the extremely fine particles which this electricity bears away with it. Now, it is in these finely divided and oxidized molecules that the origiu is found of the odour that accompanies these discharges, especially when they are intense, and when they have been continued for a long time. All the experiments cited by M. Schoenbein come to the support of this explanation. The fact that the water arrests the odour, proceeds from this, that the water intercepts the metallic emanations from the conductor; the influence of the heat that reduces the oxides ought also, as experiment has shown, to hinder the production of the odour. In fine, the two examples reported by M. Schoenbein, of a strong odour produced after the fall of the thunderbolt, are equally favourable to my hypothesis, since it is on steeples, and consequently on metallic conductors, that the lightning fell in both the cases in question.

One objection which may be presented against the explanation that I have just given, is the identity that exists between the odour produced by electricity, whatever be the nature of the metal it proceeds from. Now, if the cause of this odour resides in the metallic oxide, this odour ought to vary with the nature of this oxide. I remark first, that it is quite natural that bodies so similar as the oxides of platinum, of gold, of silver, and of copper, should have an analogous odour. Again, the sense of smell is not so perfect that it can distinguish the very delicate shades between these different odours; and in inspiring the gas which possesses the odorous principle, in such a manner as to appreciate the odour still better, by bringing into action at the same time the taste and smell,* I have found, and I am not the only one, sensible differences in the effect produced on the two organs by the principle in question; it following that if the wires which conducted the current into the acidulated water were of platinum, or of gold or silver, the impression was much more disagreeable and acrid with platinum and silver than with gold. With copper wires I have also obtained an effect, less, it is true, than with the other metals, because the oxide of copper is almost entirely dissolved in acidulated water, but this effect was likewise of a nature rather different from that obtained with platinum, or with gold or silver. In all these experiments, the water I made use of was distilled water, mixed with a small quantity of very pure sulphuric acid.

I will add again, that in operating with golden wires, I obtained at the commencement a strong odour; the gold wire made use of at the positive pole was then seen by degrees to take a reddish ap

This mode of operating was pointed out to me by M. Melly, who had it from M. Schoenbein himself, whose experiments he witnessed.

pearance, indicating that it was becoming oxidized, the oxygen gas and the odour diminishing at the same time, until the wire had taken altogether a red colour. The poles were then changed immediately; the wire, in place of remaining red, presented a pulverulent surface, due to the reduction of the oxide; and if the wire was again brought into communication with the positive pole, the odour became manifest with great force at the commencement.

I need not add, that the negative polarity of so decided a character which wires of platinum and gold acquire when plunged into oxygen charged with the odorous principle, is very probably due to the deposit of oxide in suspension, which operates on their surfaces. Now, as I have already shown, platinum in a finely developed state, when it is oxidized, is eminently negative, if it forms a voltaic pair with beaten platinum, either in wire or in plates. It is also probably to the molecules of platinum or of gold, transported by the current on the wires or plates, serving as negative poles, and where the disengagement of hydrogen completely reduces them, that the strong positive polarity which these wires and plates possess is due. This polarity is much stronger than that acquired by these metals on being simply immersed in ordinary hydrogen.

I will not conclude this first section without remarking, that the digression I have allowed myself to fall into on account of the ozone of M. Schoenbein, is connected with my subject, since the basis of the explanation I proposed is the faculty which platinum and gold possess of becoming oxidized. This is, then, an application of this property which appears to me to be not without some interest. I hope that M. Schoenbein will pardon me for differing from his opinion on a question in which, in every case, he will always have the merit of being the first investigator, and of having singularly advanced it by his numerous and beautiful experiments. In conclusion, I present my opinion with deference, and I shall be ready to acknowledge my error when pointed out to me.

MEETING OF THE BRITISH ASSOCIATION.

(Selections continued from page 138.)

"ON some new Oxides of certain of the Metals of the Magnesian Family," by Dr. Lyon Playfair.*-Dr. Playfair first adverted to our defective knowledge of the history of the magnesian oxides. Chemists were more intimately acquainted with this family than with any other; but still the actual amount of their knowledge was very scanty. Manganese, for example, possesses six degrees of oxidation; whilst magnesium, the type of the family, possesses only one, Iron and chromium possess sesqui-oxides, but copper and zinc do not

t;

• We have before alluded to this paper (page 129), but could not at that time give the particulars contained in it.-EDIT.

yet a complete identity in the structure of their molecules has been pointed out, affording new proofs of chemical analogy. Dr. Playfair showed a diagram representing all the magnesian oxides now known, in contradistinction to those which analogy leads us to expect. In this tabular statement, he denied the existence of peroxides of copper, zinc, and calcium, although it is well known that these oxides are admitted by chemists as having been discovered by Thenard. The compounds obtained by Thenard, and to which he had the general formula R O, were obtained by the action of peroxide of hydrogen on the protoxides of the metals. But these bodies did not possess any of the characters which analogy would lead us to ascribe to magnesian peroxides. In fact, they possess all the properties of peroxide of hydrogen itself: they decompose spontaneously, and detonate with combustibles. Potash accelerates their decomposition, while acids, under certain circumstances, retard it. Their action with acids is opposed to our conceptions of such unstable peroxides; for they dissolve in cold acids without decomposition, which even peroxide of manganese, stable as it is, cannot do. All these anomalous properties led Dr. Playfair to look for another composition for M. Thenard's compounds. In the course of his examination of the magnesian oxides, he found that the peroxides had a great disposition to unite with the protoxides, forming compounds of the general formula RO + R2 O4. Now, hydrogen itself is a magnesian metal, or, at all events, possesses the characters of one, and its peroxide should share the disposition to unite with protoxides. The author, therefore, drew the conclusion, that Thenard's compounds were in reality similarly composed, having the formula MO + H2O̟. And in confirmation of this view, he stated, that Thenard's own analyses coincide with it much better than with his own view of their being peroxides. This chemist obtained always too little oxygen to agree with his theory of their composition. He ought to have procured oxygen in the proportion of 36 whilst on Dr. Playfair's view, the proportion would be 3: 5, a result which approximates closely to Thenard's analyses. From these considerations, the author considered that he had a right to affirm, that the peroxides of copper, zinc, and calcium, as far as Thenard was concerned, were yet unknown, and remained to be discovered. We cannot here enter into the details of Dr. Playfair's modus operandi, and omit them with less regret since he stated, that his "Memoir on the true Peroxides," will shortly be published. We shall therefore confine ourselves to an enumeration and brief description of the compounds described by him. Peroxide of copper is of a brownish black colour. It yields oxygen on being dissolved in acids and chlorides. He obtained a hydrate of this compound oxide. By a strong heat this oxide is further decomposed. The next oxide to which the author referred, was the peroxide of iron. His attention had been directed, a few days since, o an ambiguous sentence in the " Comptes Rendus," in which M.