terwards distilled them; the first contained no ammonia, and the second yielded it as usual. It is then indispen sible to prepare the leys before they are concentrated. Lastly, neither the red oxvd, nor its sulphate, will dissolve in simple prussiate, and give to it the quality of the triple, as Scheele had found to be the case. This oxyd, although calculated to form the base of Prussian blue, is incapable of decomposing the triple prussiate, for it must necessarily be dissolved by an acid.

Recapitulation.

The prussic acid is composed of charcoal, azote, and hydrogen, in proportions, with which we are yet unacquainted. Only from the great quantity of charcoal that remains after its destruction, we may conjecture that this radical ingredient predominates; there is no indication whatever of oxygen, and indeed, when we consider the known affinities of its three elements, together with the circumstances of its formation, we cannot expect to find it.

The prussic acid itself has very few acid qualities; for it has not the sour savour; it does not redden turnsol; it is less soluble in water, the proper solvent of acids, than in alcohol, in which it is even spontaneously decomposed, without the help of the external air. It forms with the alkalies such imperfect combinations, as still to exhibit some of the qualities of the component parts; and carbonic acid, which is the weakest of all acids, will decompose it. In short, its combustibility, its savour, its aromatic odpur, its production in the midst of volatile oils and kernels, and its preservation in alcohol, comprise an assemblage of properties, that give it much more of the nature of oily and inflammable productions than of saline substances.

However,

However, the prussic acid, notwithstanding its weak sa line power, still attacks the marimum oxyd of mercury with much effect; it furnishes, with this oxyd, a saline combination so decided in its attributes, that it must be admitted that it acts, in certain circumstances, as a very powerful acid. Indeed, the prussiate of mercury possesses every quality necessary to establish it as a perfect metallic salt; it may be thought surprizing that it will not unite to the oxyd at the min mum; but by one of those effects of affinities, of which there are other examples, it is raised to an oxyd at the maximum, by reducing one part of the metal, so as to form prussiateof mercury with the other.

The pru sic acid has no effect on the red oxyd of iron, but it readily combines with the black oxyd, and produces white prussiate. It is true, that this prussiate is not perfectly white, owing to the difficulty of preparing with the green sulphate, a precipitate at the zero of superoxydation; it is always greenish, but as it becomes, in dyeing, a perfect Prussian blue, there is no doubt but that the prussic acid, with the green sulphate, perfectly free from red, would yield a prussiate as white as that obtained by the most easy means.

Prussian blue is not a simple combination, as it has been supposed; and the following observation proves it.

We know, for instance, that red oxyd forms the base of this blue; but if this oxyd alone is sufficient to make Prussian blue, why do not the prussic acid and the red oxyd produce it or the solutions of this oxyd and the simple alkaline prussiates? The fact is, that Prussian blue requires another element, which the following examples completely shew. By applying potash to Prussian blue, we obtain a yellow crystallisable salt, which has always a constant portion of black oxyd.

We

We employ the yellow prussiate, to re-produce Prussian blue, and this oxyd passes with the prussic acid into the new combination. The black oxyd then is an ele ment as necessary to the formation of crystallisable prussiate as of Prussian blue, and of all the metallic prussiates that are prepared with the triple prussiate of potash.

There are some metals capable of forming both triple and simple prussiates, such as copper, silver, manganese, cobalt, nickel, uranium, &c.; there are others that afford only the simple prussiate, such as gold, mercury, &c.; and lastly, there are some that will produce neither. But with the exception of Prussian blue and prussiate of mercury, all the others are little known and merit examination. The black oxyd united to the prus, sic acid, will pass from one combination to another without alteration. The base of this combination may even be raised from the minimum to the maximum without the black oxyd by that means undergoing any change, The combination of the acid with this oxyd is preserved by an affinity so powerful, that the alkaline hydrosul, phurets cannot separate them; or in other words, cannot unite with the oxyd in either the triple prussiate of potash or in Prussian blue.

The prussic acid, united with that portion of black oxyd which enables it to form triple prussiates, either alkaline or metallic, is a peculiar combination of which the existence cannot be doubted, but of which we have no other instance except in these prussiates.

The triple prussiate of potash cannot sustain a red heat, without losing its black oxyd, and being consequently reduced to the state of simple prussiate.

The simple prussiate may be also decomposed, but at a much lower temperature; its acid is destroyed, and reduced to ammonia and carbonic acid; it is the destruction

of

of this salt by the heat of ebullition, that injures the leys for preparing the Prussian blue.

The simple prussiate takes the character of the triple prussiate, as soon as it is exposed to combination, either with black oxyd, or a salt with a base of black oxyd, and acquires, besides the advantage of crystallising, that of being no longer decomposable by the heat of ebullition.

This prussiate, which was the test liquor so much sought by chemists, affords no Prussian blue with solutions of red oxyd, but does yield it if they contain a portion of black oxyd, because its acid attaches immediately to that portion of the black oxyd, which is necessary as an intermedium between the acid and the red oxyd.

The triple prussiate of iron, or Prussian blue, when strongly heated, is reduced to the following ingredients ammonia, the two gases carbonic and gaseous oxyd, iron in the state of steel, and charcoal.

The prussiate of mercury when decomposed affords the same products, but with the addition of a certain portion of oil.

The carbonaceous leys contain but little triple and much simple prussiate. They must not be concentrated until the second has been previously converted into triple by an addition of black oxyd or green sulphate.

To obtain from these leys all the Prussian blue they are capable of producing, it is indispensably necessary that a sulphate should be used, that contains at least a portion of green oxyd, or the simple prussiate they contain will not furnish blue with a sulphate having a base completely red.

Lastly, if this memoir is compared with Scheele's work on this subject, it will be found that all the facts herein stated were well known to him, but it appeared to me, that they required much more developement; and that is what I proposed to accomplish in this work.

Description

Description of an impro ed Instrument for ascertaining the Strength of Gunpowder.

From SONNINI'S JOURNAL.

With a Plate.

THE common powder-prover with a toothed wheel,

although the worst that is made, is in universal use, because it is the cheapest and easiest to obtain. Its evident defects are:

1. That the friction of the spring, blunts and rounds the extremities of the teeth of the wheel.

2. The spring, which is necessarily strong, and always bent, loses in time its elasticity and force.

3. The wheel being too confined in its movements, its friction is irregular, and varies also according to the state of oxydation or cleanliness of the instrument.

Whence it results, that the prover most used is in fact the most imperfect; and with the view of correcting its defects, and at the same time preserving its qualities, it bas been improved in the following manner.

A, (Plate IX.) is a wooden stock, covered with a plate of metal which sustains the apparatus.

B, a small metal mortar, for receiving the powder intended for proof. This mortar has a priming pan affixed to it.

C, a brass wheel grooved like a pulley, and furnished with 30 ratchet tectb, cut upon its circumference. This whee!, or rather pulley, carries a projector which exactly covers the mouth of the mortar B.

D, a support in which the wheel plays freely, as it turns on its axis.

E, a spring that acts as a clapper.

F,