SERIES C.

With two equal bar-magnets, placed over each other at a few inches distance, with opposite poles contiguous.

As in all the experiments of the first series, the magnetism induced on the different masses of iron was chiefly upon the portions nearest to the magnets, the influence on the opposite extremity of each portion being merely consequential, it occurred, to me, that if the substances employed in the experiments were placed betwixt the two opposite poles of a pair of magnets, so that the appropriate polarity might simultaneously be developed at both extremities of the iron, a much more powerful action might be expected. In this expectation I was not disappointed; for, adopting the arrangement represented in Pl. IV. Fig. 13, I found that experiment No. 4. could now be accomplished at distances considerably greater, and experiment No. 2. with a greater number of balls, whilst a variety of new illustrations of the phenomena of magnetic induction were successively suggested, as I proceeded with the amusing investigation.

Experiment 1.-For the vertical support of Nails and Wires on their points.

Iron-wires (a, b, Pl. IV. Fig. 14.), placed vertically on their pointed extremity, can be supported by the large magnets at the distance of two inches from the upper magnet, and the nail c, weighing 326 grains, at the distance of an inch and a half from it.

Experiment 2.-Small Figures in paper, or card board, vertically supported.

A pleasing variety is produced in the foregoing experiment, by attaching the iron-wires to little figures cut out of paper (Pl. IV. Fig. 15.), which, standing upright betwixt the magnets, and quivering on the points of the wire, are made to vibrate, or whirl round, in mimic life, by approaching them with another magnet, and waving it around them. These figures, three inches in height, can be readily sustained at the distance of an inch from the upper magnet, the magnets themselves being four inches apart.

Experiment 3.-For the support of small Wires and Nails upon each other's extremities or points.

With the large bars, four inches apart, iron-pins (the common black pins of the shops) will stand on each other two inches below the upper magnet, or three or more in a vertical series, firmly adhering to each other, and yet vibrating freely on their supporting point, whenever a small magnet or piece of iron is brought near them. a, b, c, Pl. IV. Fig. 16. represent different series of pins; d a key supported on the point of a nail, and e, two polished nails.

Experiment 4.-For the support of different articles in an upright series.

The variety of amusing series capable of being sustained under this arrangement is evidently unlimited. The forms and groups represented in Pl. IV. Fig. 17. may serve as specimens of what may be accomplished, with the articles only previously in use. The form represented at a is produced by a nail, with two half links of iron-wire suspended on its point. b is a half link of iron on the point of a nail supporting four balls near the upper magnet. The next form c represents six half links or a chain of three full links, sustained vertically. d consists of three balls upon a half link. e exhibits three balls upon the point of a nail. frepresents a nail of two inches on its point, which will not stand alone; but when the head is set round with black pins, though the heads of these are nearly an inch from the upper magnet, the whole is freely sustained. The form represented at g consists of a two-inch nail, on the point of which is an iron ball, and that ball set round with black pins, like the plume of the thistle.

Additional Observations on the Relation of Nitric and Nitrous Acids to Bromine and Iodine. By ARTHUR CONNELL, Esq. F.R.S. E., &c. Communicated by the Author.

In a late notice, mention was made of some unsuccessful attempts to oxidate bromine by means of nitric acid, by a process similar to that which effected the conversion of iodine into iodic acid *. It was farther stated, that when a small quantity of bromine was boiled with nitric acid for a considerable time in a long tube, the upper and open extremity of which was bent and terminated in water, and the intermediate part kept cool by moistened bibulous paper, so as to condense the bromine as it sublimed, and cause it to fall back into the acid, the water, after the free bromine which had passed over was expelled by heat, gave with nitrate of silver a pretty plentiful precipitate of bromide of silver. This precipitate I have since found, from an examination of the liquid in a variety of ways, was caused by the presence of hydrobromic acid; and the question arose, to what cause the occurrence of that acid could be attributed. To ascertain whether bromine was capable of decomposing pure water by similar treatment, and of so giving rise to the formation of hydrobromic acid, a little bromine was boiled with water under the same circumstances; but after the liquids employed had been deprived of colour by a gentle heat, no hydrobromic acid could be discovered by the agency of chlorine, and subsequent agitation with ether. It became necessary, therefore, to look for some third body, which, by its affinity for oxygen, might contribute to the decomposition of water; and as a coloured and fuming nitric acid had been employed, it appeared probable that nitrous acid might have that effect. Accordingly, on ma king the experiment with colourless nitric acid and bromine, and afterwards driving off free bromine from the water, in which the extremity of the apparatus terminated, by a gentle heat, no hydrobromic acid could be observed in it, when examined by means of chlorine and ether. On the other hand, when the experiment was repeated with a red and highly fuming nitric acid, the presence of hydrobromic acid in the water

• This Journal, April 1832.

was made abundantly manifest by the same reagents. A like result was obtained, when an acid was employed which had been highly charged with nitrous acid, by passing through it a current of deutoxide of azote.

From these experiments, it seems to follow that, under the influence of bromine and nitrous acid, a portion of water is decomposed by long continued boiling, hydrobromic acid, and probably nitric acid, being formed. This result is somewhat remarkable, because, under ordinary circumstances, nitric and hydrobromic acids mutually decompose one another. It does not appear that all the bromine employed becomes hydrobromic acid, a part of it being usually volatilized.

As it would appear that the precautions necessary for diminishing the loss of iodine in the preparation of iodic acid by the action of nitric acid have not been well understood *, I think it proper to add the following particulars, willingly leaving to others the determination of the comparative merits of the different methods which have been proposed for the preparation of iodic acid.

The essence of the method by nitric acid, consists in using a vessel of very large capacity in relation to the quantity of materials employed. I would recommend that it should be capable of containing forty or fifty times the quantity of nitric acid actually used. The reasons obviously are, to afford a large internal surface on which the iodine volatilized may be condensed, and from which it may be washed back again into the acid, and to diminish the quantity of acid-vapour escaping by the neck, which ought to be as narrow as possiblet. A very strong acid ought also to be employed, and the boiling is best maintained by the small flame of a spirit-lamp, so as to prevent, as much as possible, the heating of the sides of the vessel. Operating in this way, although I have always experienced some loss of iodine, yet I do not conceive that, with due care, the loss is so great as to

* See Annales de Chimie et de Physique, xlix. 144; and Annal. der Phys. xxiv. 363.

+ It is very convenient in washing back the iodine, to be able occasionally to fit in a glass stopper, so that the liquid may reach every part of the vessel, without danger of being spilt.

constitute a serious objection to the method. There are few chemical processes which are not attended with some sacrifice of materials; and it seems a matter of very little consequence on what material that loss falls, provided the total expense, in comparison with other methods, is not increased. Indeed, plans might easily be devised, by which all the iodine which escapes oxidation might be condensed, and saved for another operation. And if it be objected that the process of ebullition is tedious, I shall leave to others to determine whether more time and trouble are expended, than in the numerous steps of other methods.

It will give me much pleasure, if the suggestion of M. Serullas, whose recent loss science deplores, shall be found to facilitate the process; but in the only experiment which I have made on the subject, I could not observe that the employment of an acid, which had been highly charged with nitrous acid, by passing through it a current of deutoxide of azote, offered greater advantages.

Major-General Sir Howard Douglas, Bart. &c. on Military ·Bridges, and the Passage of Rivers in Military Operations+. THE passage from one point of a country to another, with facility, will always, among a commercial and warlike people, form a topic of general interest for discussion. In ancient times, one of the greatest obstacles to the free intercourse of one nation with another, and of different parts of the same kingdom with each other, was generally understood to arise from the bad

* I speak here of the result of my own experiments, which were not conducted with any particular view to economy; but I observe that M. Duflos, in following out these experiments, has succeeded in converting half an ounce of iodine into iodic acid, by means of 24 ounces of nitric acid, without any loss of iodine at all.-Bullet. des Sciences, Oct. 1831.

+ This article is to be considered as illustrative of the highly interesting and very important work, entitled, "An Essay on the Principles and Construction of Military Bridges, and the Passage of Rivers in Military Operations." By Major-General Sir Howard Douglas, Bart. &c. Second edition, pp. 417.