Графични страници
PDF файл
ePub

abstract. We have seen that all the alchemical authorities agree in the description of certain preliminary results as necessary to the completion of the great work, and as indisputable prognostics of success. The philosopher, therefore, believed himself to be in the way, if he had obtained the means of keeping up and moderating the heat of his furnaces, if he had effected a seeming fixation of mercury or its calces, or extracted a tincture, produced any thing, that is, solid or liquid, approaching to the deep-red or orange colour, supposed to be characteristic of gold. Yet more if he had procured a ponderous result of a ruby-like tinge, or even if the materials on which he operated underwent certain changes of colour in the process, did he flatter himself that he was not far from the great desideratum.

However these signs of the work may have been in their day sufficient inducements to so unreasonable and unprofitable a waste of time and means, your readers will have no difficulty in understanding, that they might any, or all of them, manifest themselves repeatedly in the complicated and lengthened operations of the experimentalist, without bringing him one hair's breadth nearer to the fabrication or possession of Gold.

I am, dear Sir, very truly yours,
J. J. CONYBEARE.

ARTICLE VII.

Astronomical Observations, 1823.
By Col. Beaufoy, FRS.

Bushey Heath, near Stanmore.

Latitude 51° 37' 44.3" North. Longitude West in time 1' 20.93",

[blocks in formation]

ARTICLE VIII.

On Thermomagnetic Rotation. By the Rev. J. Cumming, MA. Professor of Chemistry in the University of Cambridge.

(To the Editor of the Annals of Philosophy.)

MY DEAR SIR,

Cambridge, Nov. 18, 1823.

IN the Annals of Philosophy for September, you did me the favour to insert a notice of two instruments for exhibiting the rotation of wires by thermoelectricity; the magnet being applied externally in the one, and internally in the other.

The parallelogram of silver and platina to which the magnet was applied externally, was attached to an agate cap, and the whole poised on the point of a long needle, in which case a counterpoise was obviously necessary. I have since found it more convenient to bend the parallelogram into the form of a semicircle, having the agate cap nearer to the wire than the centre of the circle.

A lamp and magnet being placed opposite to each other are sufficient to produce rotation; but the effect is improved by adding another magnet at 90° from the first, having its poles in the contrary direction, and being connected with it by a bar of soft iron placed beneath them. With this arrangement, the rotation will be from right to left, or from left to right, according to the position of the lamp.

A B, platina; BCFDA, silver; E, agate cap.

The second magnet is placed near F G, having its N end upwards.

If the lamp be applied beneath B, the rotation is in the direction B GA; but if it be opposite to F G, the rotation is AGB. The annexed figure represents the apparatus, which, exclusive of the agate cap, weighs about four grains.

PS. If six parts of bismuth, and one of antimony in powder, mixed together, and inclosed in a glass tube, be touched by a hot wire connected with the galvanoscope, the deviation is first positive,

S

N

B

F

A

طح
1

G

and then negative, as I have before mentioned to be the case with the alloy of these metals melted together in the same proportions. I am, dear Sir, very truly yours,

J. CUMMING.

ARTICLE IX.

On the Crystalline Forms of Artificial Salts.
By H. J. Brooke, Esq. FRS.

(Continued from p. 375.)

Sulphate of Zinc.

I AM indebted to Mr. Teschemacher for some brilliant and remarkably perfect crystals of this salt, which may be cleaved parallel to the plane h of the annexed figure,

but I have not observed distinct cleavages

in any other direction.

The primary form is a right rhombic prism.

[merged small][ocr errors][merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

I received some time since from Mr. R. Phillips some crystals of this salt, which were right rhombic prisms; and shortly afterwards Mr. Cooper supplied me with others which were square prisms. On noticing this difference of form, the first idea that suggested itself was, that there might be some difference in the proportion of water in the two salts, as both Mr. P. and Mr. C. were satisfied, from the manner of preparing them, that both must be free from impurity. The surfaces of the square prisms obtained by Mr. Cooper not being so brilliant as might be desired, he dissolved some of these crystals in distilled water, on the evaporation of which he was surprised to find it deposit rhombic prisms similar to those I had received from Mr. Phillips, and without the intermixture of a single square prism. On learning this fact, Mr. Phillips examined the solution from which his first crystals had been obtained, and he found that it had since deposited together others of each of these forms, and the crystals of each were observed frequently to inclose smaller ones belonging to the other class.

On these differences of form being discovered, Mr. Cooper and Mr. Phillips analysed several quantities of the crystals of each, and obtained nearly corresponding results, as will appear from a paper by Mr. Phillips immediately following this. Previously, however, to their analysis, Mr. Cooper reduced to minute fragments, and exposed to the air for several days, each

of the quantities he was about to examine, and he found that the rhombic prisms had lost one atom of water, while the square prisms experienced no loss. As the square prisms formed in Mr. Phillips's solution were not deposited until that had been much reduced by evaporation, it appeared probable that an excess of acid might be necessary to their production. Mr. Cooper, therefore, dissolved some of the rhombic prisms in dilute sulphuric acid, and from this solution square prisms were obtained. Thus it was ascertained that either the square or the rhombic prisms might be produced at pleasure, by crystallizing the salt from a solution in dilute sulphuric acid, or in water.

It appears from the analyses of the two sets of crystals, that between 1 and 2 per cent. of the water of the rhombic prisms has been replaced by sulphuric acid in the square ones. But as this difference does not constitute any atomic disparity of composition in the two forms, we may probably ascribe their difference to some cause analogous to that which has impressed on arragonite a crystalline form distinct from that of common carbonate of lime.

Sulphate of Nickel in Rhombic Prisms.

The form and measurements of this salt approach so very nearly to those of sulphate of zinc, that I am inclined to doubt of there being any real difference between them. If there be any, it will not exceed 2' or 3' in the inclination of M on M', which, in many of the crystals of this salt approaches nearer to 91° 10′ than to 91° 7'. We may, therefore, refer to the measurements given above for the angles of these crystals. But there is a difference in the cleavages of the two salts, for this may be cleaved easily parallel to its lateral primary planes.

Sulphate of Nickel in Square Prisms.

This is the form of the crystals of this salt alluded to by Dr. Wollaston in a paper which appeared in the Annals of Philosophy, vol. 11, p. 286, but without any measurements. The crystals may be cleaved parallel to the planes P, M, and M', of the accompanying figure, which are its primary planes.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small]

a2

[ocr errors]

Sulphate of Nickel and Potash.

This salt was first given to me by a friend as sulphate of nickel,

and I afterwards received some good crys tals of it from Mr. Cooper, as a double salt. The primary form is an oblique rhombic prism.

[merged small][merged small][ocr errors][merged small][merged small][ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small]

Observing the similarity of the forms of one of the sulphates of nickel and of the sulphate of zinc, Mr. Phillips dissolved equivalent proportions of the two salts in water, and obtained from the solution a new salt, having the same form and measurements as the crystals which had been dissolved. I have attempted to cleave several crystals of this double salt, but without discovering any decided cleavage planes in any direction.

ARTICLE X.

Analysis of the Sulphates of Nickel, described in the preceding Paper. By R. Phillips, FRS. L. and E. &c.

SULPHATE of nickel has been several times analysed; my intention, therefore, in subjecting this salt to examination was to attempt a discovery of the causes to which the different crystalline forms it presents are referable. The composition of sulphate of nickel is stated as follows by

[merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

One hundred grains of the crystals of this salt, in the form of rhombic prisms, were dissolved in water, and decomposed by nitrate of barytes; the sulphate of barytes obtained, taking the mean of two experiments, weighed 83.08 grains, equivalent to 28.16 of sulphuric acid.

Of the same salt 100 grains were decomposed by soda, and the precipitated oxide of nickel, after the requisite washing, was dried and ignited. It weighed, 26:3 grains. I repeated this experiment, and obtained rather more oxide, but I had afterwards reason to suppose that the sulphate of soda formed had not been

« ПредишнаНапред »