nos 849 and 850.

Mr Berthollet, the inventor of fulminating silver, having contented himself with a general and concise description of this subject, many practical chemists have failed in their attempts to prepare it; and others, forming their opinions from the specimens which they had made, have been exposed to great danger; as will appear from the following relation:

An ounce of fine silver was dissolved in the course of eight hours in an ounce of pure nitrous acid, of the London Pharmacopoeia, diluted previously with three ounces of distilled water in a glass matraix. The solution being poured off, the residuary black powder and the matraix were washed with seven or eight ounces of warm distilled water, and this was added to the solution. The black powder, being gold, was rejected; some gold being thus separable from any silver of commerce.

To the foregoing diluted solution, pure lime-water prepared with distilled water was added gradually; for the solution ought not to be poured into the lime-water. When about thirty pints of lime-water had been expended, and the precipitate had subsided, more lime-water was added, by successive pints, as long as it caused any precipitation. For it was deemed fitter that the precipitation should not be perfected, than that an excess of lime-water should be used; the earthy pellicle of the excessive lime-water being apt to mix with the precipitate. The clear liquor being poured away, the precipitate was poured off, and washed into a filter.

When the saline liquor had drained from it, two ounces of distilled water were poured on the magma; and when this water had passed, fresh portions were successively added and passed, until the whole quantity of water thus expended in washing away the nitrous calcareous salt amounted to a quart.

The filter being then unfolded, to let the magma of oxyd of silver spread on the flattened paper, it was placed on a chalk-dome to accelerate the evaporation, and was gradually dried in the open air; a cap of paper being placed loosely over it to exclude the dust.

When the weather fared, the cap was removed, to expose the oxyd to the rays of the sun; although this was not deemed necessary; and evaporation was promoted by cutting the oxyd into thin slices. When perfectly dry it weighed 1 oz. 4 dwt., and about one-fifth of it was considered as oxygen.

When aqua ammonia pure of any pharmacopoeia is used with this oxyd, either in the small quantity which blackens it completely, or in a greater quantity, the black matter which subsides, and which has been represented by systematic writers as the fulminating compound, has no such property, any farther than may be owing to the matter deposited from the alkaline solution during the evaporation.

The alkaline liquor containing the fulminating silver ought to be poured off from the insoluble powder, and exposed in a shallow vessel to the air. In consequence of the evaporation, black shining crystals form on the surface only, and soon join to form a pellicle. As this pellicle adheres a little to the sides of the vessel, or maintains its figure, the liquor may be poured off by a gentle inclination of the vessel.

This liquor will yield another pellicle in the same way; but the third or fourth pellicle will be paler than the former, and weaker in the explosion. The first pellicles, when slowly dried, explode by the touch of a feather, or by their being heated to about 96°.

The quantity of water in the ordinary aqua ammonia pure renders it less active in the solution of the oxyd, and is an impediment to the speedy formation and separation of the fulminating silver; and an experimenter who has often used twenty grains of the oxyd to produce successive pellicles of fulminating silver, which may be separately exploded with safety, and who has perceived that the pellicles never explode whilst wet, if they be not heated, would, in all probability, resolve on the following improvement, and expose himself to the unforeseen danger of it.

Distilled water was impregnated with as much pure ammonia as it could easily retain under the ordinary temperature of the air. A quantity of this strong ammoniacal liquor, equal in bulk to a quarter of an ounce of water, was placed in a small bottle, and 24 grains of the oxyd of silver, ground to fine powder, were added. The bottle, being almost filled, was corked, to prevent the formation of that film which usually appeared in consequence of the exhalation of the ammonia in other experiments.

During the solution of the oxyd, bubbles of the gaseous kind arose from it, and the solution acquired a blue colour. As no film appeared, the bottle was agitated three or four times in the course of as many hours, in order to promote the solution of a small quantity of blackened oxyd which remained at the bottom. The experimenter considering this as an ample provision for twenty different charges, to be exploded in different circumstances, in the presence of the society, intended to pour off the solution into as many small vessels, and to weigh the residuary black powder, after allowing two hours more for the solution.

On the fifth hour he took his usual precaution of wearing spectacles; and observing that a small quantity of black powder still remained undissolved, and that no film was yet formed at the surface, he took the bottle by the neck to shake it; knowing that it might explode by the heat of his hand, if he were to grasp it, and that the explosion in this circumstance might wound him dangerously.

In the instant of shaking, it exploded with a report that stunned him. The bottle was blown into fragments so small as to appear like glass coarsely powdered. The hand which held it was impressed as by the blow of a great hammer, and lost the sense of feeling for some seconds; and about 52 small grains of glass were lodged, many of them deeply, in the skin of the palm and fingers. The liquor stained his whole dress, and every part of the skin that it touched. Thus it appeared that fulminating silver may be made which will explode even when cold and wet, by the mere disturbance of the arrangement of its parts, in the aqueous fluid.

In subsequent experiments, privately and carefully conducted, it seemed that the property of exploding in the cold liquor, by mere commotion, depended on the unusual quantity or proximity of the explosive molecules in a given bulk of the liquor. And the flat bottoms, as well as the sides, of the thick vessels of glass or pottery-ware, whether they stood on boards or iron plates, were always beaten to small fragments.

This afforded a curious instance of the possible equilibrium between the powers tending to retain the caloric and those which effect the expulsion of it; and experiments and considerations of this kind seemed to promise a true solution of the phenomena of Rupert's drops.