soda throws down at first the arseniate of iron, and then any simple peroxide that may remain, if more muriate of iron was added than was necessary to afford sufficient peroxide of iron to saturate the arsenic acid. The arseniate of iron is yellowish white, the simple peroxide brown-red, showing that no arsenic acid remains in the solution, if the ferrugineous precipitate, after being yellowish white, appears red in the last portions; and indeed if this does not happen at first, more of the muriate of iron should be added, till the brown-red precipitate shows itself. All the arsenic acid and oxide of iron being thus got rid of, nothing but nickel and cobalt remains in the solution, which must then be separated. The process of M. Laugier answers this purpose completely; but, as M. Tuputi observes, where it is only desired to procure a quantity of pure oxide of nickel, without regard to accuracy of analysis, it is a much cheaper and simpler method to add an alkaline subcarbonate to the solution of the two metals; which first throws down the pure rose-coloured oxide of cobalt, then a mixture of the two metals, and lastly pure oxide of nickel. When only the latter is left in the solution, it is to be boiled with an alkaline subcarbonate, and the precipitated oxide well washed.

Arseniate of Nickel.

To prepare this salt, 1.96 gramme of oxide of nickel was dissolved in muriatic acid, three grammes of arsenic acid in water were added, and then precipitated by a subcarbonate of alkali, and the whole was filtered and the liquor boiled, to throw down the small quantity of arseniate held in solution by the carbonic acid. The arseniate of nickel thus obtained, weighed after calcination 3.91 gr. being exactly double the weight of the oxide of nickel. To recover the remainder of the arsenic acid, one gramme of peroxide of iron in muriatic acid was poured in, and the arseniate of iron was precipitated by an alkali; it weighed 1.97 gr. of which consequently 0.97 gr. was arsenic acid. A loss of 0.08 gr. appears in this operation: nevertheless it may be concluded that arseniate of nickel contains nearly equal parts of acid and oxide-a result confirmed in various ways.

From the known composition of protoxide of nickel and of arsenic acid, it is obvious that the arseniate of nickel, separated by the carbonates from its solution in acids, is a sub-salt, containing one and a half as much base as the neutral arseniates. The same takes place with the arseniates of cobalt, copper, and peroxide of iron obtained in the same way, but not with the arseniate of lime precipitated from its acid solutions by a great excess of ammonia.

Ten grammes of arseniate of nickel heated in a crucible lined

with charcoal, as in iron assays, gave a well-melted button of arseniuret of nickel weighing 6.15 gr. It was grey without any tint of red, brittle, the fracture granulated, almost even, and somewhat approaching to lamellar; in its centre it contained a cavity lined with brilliant needles; it was not at all magnetic. This compound contained nearly a half part less of arsenic than the native arseniuret of nickel, and consequently one atom of arsenic to two of nickel.

The Sulphate of Nickel crystallizes in long oblique prisms with rhomboid bases, and changes into hexaëdral prisms by a facet on each obtuse angle. These crystals are perfectly transparent, and of a beautiful emerald green. By exposure to air and solar light they gradually effloresce, and become opake without losing their form. When calcined, this sulphate was composed of 0.478 per cent. of protoxide of nickel, and 0-522 of sulphuric acid. Ten grains of this sulphate reduced in a charcoal crucible at the heat of an iron assay, gave a well-melted button of sulphuret, which was grey with a shade of yellow, brittle, with a fracture lamellar in one direction, and granulated in the other, and strongly magnetical. It appears to consist of 1 atom of sulphur and 2 of nickel.

The Carbonate of Nickel obtained by precipitating a solution of this metal with a subcarbonated alkali, is of a fine apple-green verging to yellow, and retains this colour after exposure to the sun. If it contains ever so little cobalt its tint is sensibly altered, and passes to a dirty greyish violet.

Protoxide of nickel.....

It is composed of

Carbonic acid...

Water ..

This salt appears to contain 1 atom of acid to 1 atom of oxide. When a saturated carbonate instead of a subcarbonate is employed, the precipitate is of a very pale green, and becomes light and pulverulent when dried in the sun.

It consists of

Protoxide of nickel
Carbonic acid

Water ....

0.483

0.210

0.307

It appears to contain 3 atoms of acid to 2 of base.

-1.000

These carbonates of nickel are readily decomposed by heat. When they are calcined in a dull red heat with exposure to air, they produce a fine black peroxide of nickel, but in a stronger heat this changes to a pure olive-coloured protoxide.

XLVI. Notices respecting New Books.

An Analytical Calculation of the Solar Eclipse for the 7th Day of September 1820. By D. MACGREGOR. 8vo. pp. 46. 3s. THERE is scarcely any circumstance so well adapted to excite in the minds of the unscientific an exalted opinion of Astronomy, as the power which its professors enjoy, of predicting to the greatest nicety the various phænomena of an eclipse. And even among those who have in some degree studied this sublime science, there is no doubt a considerable number, whose attainments will not enable them to go through the various calculations which are required upon such an occasion.

We have been led to this remark, by the examination of a pamphlet recently published, entitled "An Analytical Calculation of the Solar Eclipse for the 7th of September 1820. By D. MacGregor." 8vo. pp. 46. The Author professes to have printed this work "not with the view of instructing mathematicians or astronomers; but of assisting those who are not yet sufficiently conversant in these subjects, and who are desirous of being better acquainted with them." And certainly we have not observed in any elementary work, or Cyclopædia, a more clear elucidation of the calculus of a Solar Eclipse than is here presented to the reader.

The first step taken, is, to ascertain, nearly, the time of New Moon, which is done by Burckhardt's formula given at the end of his Lunar Tables; and consisting of twelve terms. For the epoch thus found, are calculated (from the last-mentioned tables) the moon's true longitude, latitude, horary motion, horizontal parallax, and semi-diameter; and from Delambre's solar tables, the sun's longitude, horary motion, horizontal parallax, and semi-diameter. The computed longitudes of the two luminaries being then compared together, the difference is no more than 2"; and the correction of the time of conjunction found by the formula, only +44 seconds of time.

The next step is to compute, by spherical trigonometry, the Right Ascensions and N. Polar distances of the two luminaries; and the first portion of the process is concluded by the forination "Table of data for the general eclipse," in which the principal quantities already enumerated are set down for every 30 minutes of the duration of that phænomenon.

of a

The Author proceeds, in the second part, to give formulæ for the solution of eight problems relating to the eclipse, as affecting the earth generally, but without numerical examples; and then passes to the third portion, which occupies 25 pages, and contains five general analytical solutions, which have for their ob

ject

ect the determination of the phænomena of the Eclipse at any particular place. These are followed by an actual logarithmic computation of every particular, so as to render the application. of the formulæ clear to every one possessing but a moderate knowledge of analysis.

Upon the whole, we think that every lover of the science, who does not possess the original works from whence the formulæ are extracted, will be anxions to procure this interesting pamphlet, which, from the transient form in which it appears, will probably soon become scarce.

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