Fulminating gold

Aurum Fulminans

If a solution of chloride of gold be precipitated by an excess of ammonia, a yellow powder will be obtained, which, when heated, or only bruised, explodes suddenly with a prodigious report. The force of this aurum fulminans is terrible, and, in the hands of incautious persons, has often occasioned much mischief. But, however powerful, it cannot, as some have imagined, be employed instead of gunpowder, even were not this impossible on account of the high value of the metal from which it is made; for explosion does not take place when the powder is confined. Phænomena of this kind are always of importance, and afford subject of speculation to the philosopher, though no immediate use can be made of them 1584. Experiments, however, have rendered it probable that this powder may possess some medicinal virtues, and we are assured that it can be employed in enamel-painting.

He who attempts to trace out the invention of aurum fulminans is like a person bewildered in a morass, in danger every moment of being lost. I allude here to the immense wilderness of the ancient alchemists, or makers of gold; to wade through which, my patience, though pretty much accustomed to such labour, is not sufficiently adequate. Those who know how to appreciate their time will not sacrifice it in endeavouring to discover the meaning of books which the authors themselves did not, in part, understand, or to comprehend passages in which the writer tells us nothing, or, at any rate, nothing of importance. I have, however, made my way through this labyrinth from Spielmann to the works which are ascribed to Basilius Valentin 1585.

The period when this powder was invented is as uncertain as the accounts given of its composition. It is however probable that the discoverer was a German Benedictine monk, who lived about the year 1413 1586 ; and there is reason to think that he may have made many useful observations, of which we are yet ignorant. When new observations have been made respecting gold, they have always been found afterwards in the works of Valentin, in a passage which no one before could understand. Such writings are of no more utility than the answers of the ancient oracles, which were comprehended when a knowledge of them was no longer necessary, and which misled those who supposed that they comprehended them sooner. But the account of aurum fulminans in Valentin is so uncommonly intelligible, that it almost seems he either wrote in an explicit manner without perceiving it, or that the words escaped from him contrary to his intention. As the work in which it may be found is scarce, I shall transcribe the prescription 1587 :—

“Take a pound of aqua regia made with sal-ammoniac; that is, take a pound of good strong aquafortis, and dissolve in it four ounces of sal-ammoniac, and you will thus obtain a strong aqua regia, which must be repeatedly distilled and rectified until no more fæsces remain at the bottom, and until it becomes quite clear and transparent. Take fine thin gold-leaf, in the preparation of which antimony has been used; put it into an alembic; pour aqua regis over it; and let as much of the gold as possible be dissolved. After the gold is all dissolved, add to it some oleum tartari, or sal tartari  dissolved in a little spring-water, and it will begin to effervesce. When the effervescence has ceased, pour some more oil into it; and do this so often till the dissolved gold falls to the bottom, and until no more precipitate is formed, and the aqua regia remains pure and clear. You must then pour the aqua regia from the gold calx, and wash it well with water eight or ten times. When the gold calx is settled, pour off the water, and dry the calx in the open air when the sun shines, but not over the fire; for as soon as this powder becomes a little heated or warm, it explodes, and does much mischief, as it is so powerful and violent that no man can withstand it. When the powder has been thus prepared, take strong distilled vinegar and pour over it; keep it continually over the fire for twenty-four hours, without stirring it, so that nothing may fall to the bottom, and it will be again deprived of its power of exploding; but take great care that no accident happens by carelessness. Pour off the vinegar, and, having washed the powder, expose it to dry.”

The latter part of the receipt shows that Valentin had made experiments in order to discover how aurum fulminans might be deprived of its power of exploding, and he found that this could be done by vinegar. It appears from his writings that he had discovered also that the same thing could be effected by sulphur 1588.

After the time of Valentin, Crollius, who lived in the last half of the sixteenth century, seems to have been best acquainted with this powder, and to have principally made it known 1589 : at any rate his works are referred to by most of the modern writers. He calls it aurum volatile, and speaks of its being useful in medicine. The name aurum fulminans  was, as far as I know, first used by Beguin 1590. The method of preparing it is described by Kircher, who considers it as a thing uncommon, and who calls it pulvis pyrius aureus 1591 .


1584  [That this and other similar chemical phænomena may be of more advantage than as affording merely subjects for speculation to the philosopher, although not immediately applicable to any useful purpose, may be inferred from the valuable application of fulminating mercury, a somewhat similar compound to that under consideration. This, at first, as with fulminating gold at present, was a mere curiosity; it has recently caused the almost complete substitution of percussion for flint locks in fire-arms, which in addition to the greater certainty caused by the increased rapidity of the discharge, œconomises the quantity of powder requisite.

Fulminating mercury is made by dissolving mercury in nitric acid and pouring the solution into warm alcohol. Effervescence ensues. When this has ceased, the mixture is poured upon a filter, and well-washed with water; after draining, the filter is expanded upon plated copper or stone-ware, heated to 212° by steam or hot water. Dr. Ure recommends that the powder be mixed with a solution of mastic in spirits of turpentine, to cause attachment. Its extensive use in making percussion-caps is well-known. It is however a very dangerous substance to experiment with, owing to the readiness with which it explodes, and has caused many very serious accidents.]

1585  Spielmann, Institut. Chem. p. 288.

1586  See Preface of B. N. Petræus to the Works of Valentin, Hamb. 1717, 8vo.

1587  Fr. Basilii Valentini Letztes Testament; Von G. P. Nenter. Strasb. 1712, 8vo, p. 223.

1588  See Bergmann on Pulvis fulminans, in his Opuscula Physica et Chemica, 1780, 8vo, ii. p. 133.

1589  O. Crollii Basilica Chymica. Franc. (1609), 4to, p. 211.

1590  J. Beguini Tyrocinium Chymicum was printed for the first time at Paris, in 1608, 12mo. In the French translation, Les élémens de chymie, revues, expliquez, etc., par J. L. de Roy; Paris, 1626, 8vo, the receipt for making or fulminant  may be found p. 314.

1591  Kircheri Magnes. Coloniæ, 1643, 4to, p. 548. The author says that he found the receipt for preparing it in Liber insignis de incendio Vesuvii. That I might know whether this work contained anything respecting the history of aurum fulminans, I inquired after it. Kircher undoubtedly meant Incendio del Monte Vesuvio, di Pietro Castelli; in Roma 1632, 4to: but the directions given there, p. 46, for making oro fulminante, are taken from Crollius. Nothing further is to be found in Kircher's Mundus Subterraneus.