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then the cloth replaced for half an hour without agitation: the cloth is then to be placed on the wheel, the bath heated, the cloth passed through, and then taken away and passed through cold water.

iii. Milling. This is to be done at common temperatures, with a solution of 1 part of soap in 20 parts of water for 20 parts of cloth by weight.

iv. Brightening. The brightening of deep blues is done by plunging the cloth for twenty-five or thirty minutes in water containing one three-hundredth of its volume of ammonia. As this gives too grey a hue to clear blues, an acid water consisting of 5 parts of cream of tartar dissolved in 10 parts of water and added to 1000 parts of water, is prepared for them. This is heated by steam, and the cloth passed through it for twelve or fifteen minutes, after which it is washed in running water.

A kilogramme (about 21 lbs.) of cloth dyed blue in this manner costs 1 francs, whilst dyed with indigo it would cost more than double. Prussian blue thus applied on wool resists the action of cold water, of air, the sun, friction; has the characters of a good solid colour, and more lustre than indigo.

The commissioners proved by their own experiments that the pertartro-sulphate of iron is a very proper agent for the transference of oxide of iron to wool, and may be in this respect employed with great advantage in many dyeing operations.

M. Raymond also remarks a peculiar change in the mechanical properties of wool occasioned by chlorine. When passed through a bath of that substance in solution, the wool becomes silky and loses its property of felting; a change which, though it might be advantageous sometimes, would occasionally be very inconvenient and injurious.-Révue Ency. xxxix. 779.

§ II. CHEMICAL SCIENCE.

1. Electro-chemical Theory of Combination.-One part of this theory, according to certain persons, supposes that elements capable of combining are in opposite states of electricity; that when they combine, the electrical attractions draw them together, and that in the act of combination these electricities mutually neutralize each other. The discharge of the electricity has been considered as the source of the heat and sometimes light evolved, as in combustion. This view involves the difficulty, that after the electricities are neutralized the attraction supposed to depend upon them still continues. Upon this, M. Fechner remarks, that the difficulty no longer exists if it be supposed that there is a separation of electricity equivalent to a discharge before the particles come into actual contact. On this view chemical light and heat are not the consequence of the union of different electricities, but of their separation. When two combining particles are found within the distance of molecular attraction they will always remain in opposite states of electricity,

even after the separation of the two electric fluids has happened, just as occurs with two voltaic piles. The two particles would approximate and even come into perfect contact were it not for the repulsive power of heat which keeps them separate, and prevents the neutralization of their electricities.-Jahrb. der Phys.-Bull. Univ. A. x. 150.

2. Chemical Powers of Magnetism.-The following experiment is by the Abbé Rendu. If a bent glass tube be filled with the tincture of red cabbage and two iron wires suspended to the poles of a magnet be immersed in the liquid in the two branches, the tincture will, in a quarter of an hour, become blue or of a deep green* in both branches of the tube, although the magnetism of the two wires must be of different kinds. The same result is produced if well tempered and polished steel needles be used in place of the wires. If one wire be removed, the effect takes place only in the other branch of the tube where the wire remains. The same results occur if the wires are not in contact with a magnet; but being then cleaned they are found to have become magnetic. Tincture of litmus undergoes similar changes, but far more slowly, and the colour becomes green only in the leg containing the north wire.

M. Biot considered that the oxidation of the wires might in these cases produce the ordinary effects of a voltaic current, but that as magnetism exerted its influence notwithstanding the presence of interposed bodies, he advised M. Rendu to separate his wires from the tincture by small glass tubes closed at their lower extremities. In this case even, according to M. Rendu, the same phenomena were produced, but much more slowly. The tincture of red cabbage, however, became perfectly green in two days.— Mem. de Savoie.-Bull. Univ. A. x. 196.

3. Effect of Magnetism on the Precipitation of Silver.-The following very singular results (if correctly reported, and there seems to be no reason to doubt them in that respect) strikingly illustrate the influence exerted by magnetism over the precipitation of silver. All of them were made by Professor Muschman, and some so early as 1817. A glass syphon, half an inch in diameter and fixed with its angle downwards, had mercury poured in so as to cover the lower part, but not prevent free communication between the two legs, and then a solution of nitrate of silver of specific gravity 1.109 was poured in so as partly to fill both legs. The syphon was placed accidentally in the plane of the magnetic meridian; in a few minutes the silver was precipitated, and, to the surprise of the observer, more abundantly and with more brilliancy in the leg towards the north than in the other.

*The resemblance of salts of iron to alkaline solutions in their effects on vege table colours has been noticed long ago, and must not be forgotten here. See Quart. Journal, vol. xiii. p. 315.

OCT.-DEC. 1828.

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As no other cause than terrestrial magnetism could be perceived likely to produce this result, the experiment was repeated with syphons of the same diameter, but having legs twelve inches long. Two simultaneous experiments were made, in one of which the syphon was made to coincide with the plane of the magnetic meridian, as before; in the other, the syphon was perpendicular to this direction. The two were placed in the same chamber on the same table, and in the same relation to light, air, &c. The silver began to precipitate first in the former of these syphons; the metal rose in the north branch with greater brilliancy, in larger quantity, and in larger needles than in the southern branch. The silver in the latter seemed as if fused, was scarcely at all radiated in form, and was mixed with much mercurial salt that collected on this side. In the other syphon, there was no change in less than twelve hours, after which the silver began to precipitate slowly, but equally in both limbs of the instrument. Next morning the first syphon had deposited all its silver; in the other a deposition still went on; the latter was placed therefore on another table, with the south pole of a magnet under one of its legs. A day after it was clearly seen that the silver had passed in the direction of the magnet, and rose higher in that limb than the other. These experiments, repeated many times with different sized syphons, always give the same result.

For the purpose of giving the silver more freedom of choice during its precipitation, circles were drawn with tallow upon small plates of glass, solution of nitrate of silver placed on the glass within the circles, and a rounded piece of zinc placed in the centre of each solution. The silver immediately began to precipitate in circular zones, but so that the circles always extended much more towards the north than in the other directions; the zinc and its oxide passed towards the south. These experiments, repeated, always gave the same results.

Plates of glass, similarly charged with solution and zinc, were then placed about two metres from the poles of strong artificial magnets, whilst similar plates were preserved at a distance. The effect was striking on the plate placed near the south pole of the magnet, for the silver passed towards the pole with great rapidity, and was entirely precipitated in one-fourth of the time necessary for the solution on the distant plates.

In the experiments with magnets it may be supposed that the conducting power of the iron may have some effect analogous to that observed by Zimmerman, when metallic precipitations took place in the vicinity of conducting bodies; but in the experiments without magnets, the influence of terrestrial magnetism appears no longer doubtful.

M. Muschman then refers to a disposition of metals in the bowels of the earth, perhaps referable to a similar cause. A vein of metallic silver is found at Königsberg, in the Fall-band, which extends from north to south. The presence of the silver is always indi

cated by the occurrence of a certain quantity of pyrites and blend. May one not be led to conclude, that the silver was originally united with the sulphur, but that, by the effect of terrestrial magnetism, it has been carried towards the copper and zinc, or, in other words, that the vein occurring in the direction of the magnetic meridian, the magnetic force has produced a similar effect in it to that occurring with a platina wire in the voltaic circuit?—Ann. de Chimie, xxxviii. 201.

4. On the Magnetism of Galvanometer Wires, and of Metals generally. Every electrician is acquainted with the beautifully delicate galvanometer, contrived by M. Nobili, in which two magnetic needles nearly neutralize each other's tendency to point in obedience to the earth's magnetism, and are conjointly acted upon by a wire conducting voltaic electricity, so as by their deflection to indicate the presence and force of the current in the wire. M. Nobili has often observed that the needle of his instrument, when out of use, instead of pointing to zero, and taking up a position parallel to the conducting wires, deviated to the right or the left, sometimes by as much as 15° or 20°. This deviation only occurred in those instruments, which were so thoroughly neutralized, that the earth possessed scarcely any directive influence over them. On examining the wires of the galvanometer no iron could be detected in them, and, after much research, M. Nobili concluded that the effect was due to an attraction exerted by the copper wires of the instrument, analogous in its nature to that observed by M. Arago between the magnetic needle and various metals*. Six or seven copper wires, about one hundredth of an inch in diameter, being united and placed about the twenty-fifth of an inch from the needles in the plane of their motion, drew them from 15° to 20° from their place of rest, when uninfluenced. The same effect took place with platina wires, but more weakly; silver wires were found to be almost without action on the galvanometer needles. By using silver wires M. Nobili was able to construct a galvanometer, far more sensible than with wires of any other metals, in consequence of its freedom from interfering action. This instrument he intends shortly to describe.-Bib. Univ. 1818, p. 79.

5. Early History of Electro-Magnetism.-In the year 1801 Gautherot brought two fine pianoforte strings in contact, one with the upper and the other with the lower, end of the pile, keeping the extremities fluttering in the air. When these ends touched each other, he says (Ann. de Chimie, xxxix. 209,) “A very decisive adhension took place; they seemed united as by a magnetic power, which was so strong, that he could move the united wires in every direction to a distance of some centimetres." Thus it may be seen that, in the investigation of nature, a few detached observations are

* According to M. Arago, this is rather a repulsion than an attraction:-ED.

insufficient; but that they must be pursued and combined, by which means it was that Oersted became the discoverer of electromagnetism.-Schweigger's Jahrbuch, 1828.

We can see nothing in the above effect at all resembling, or dependent upon, electro-magnetism. The attraction at first, if there were any, was common electrical attraction, well known to be exhibited by the voltaic poles. The after-adhesion was, most probably, the result of slight fusion at the place of contact-certainly, not of electro-magnetic attraction.-ED.

6. Intense Light.-The intense light produced by igniting lime in the oxy-alcohol flame, is well known, and has been beautifully applied in the construction of geodesical signals by Lieutenant Drummond. It is said, that a very ready mode of exhibiting it on a small scale is, to place a small piece of lime on charcoal, lighted, at the spot by a little piece of tinder, and throw a jet of oxygen from an ordinary blow-pipe aperture upon it.

7. Table of atomic weight of Bodies, by Berzelius.-The table by Berzelius is stated to be according to the most recent and exact analyses. We do not think it necessary to give any more of it than that part which relates to hydrogen as unity. The atomic numbers adopted by Berzelius are often double, and sometimes triple and quadruple those of other chemists; but these cases generally explain themselves, and, for the simple substances in the following list, are marked by preceding figures:

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