This Marcus speaks of saltpetre three times; first under the name of sal petrosum, which occurs also in the same prescription in Albertus Magnus; but the addition, which Albertus does not repeat, is very remarkable. In my opinion, scrophulæ contra lapides means the incrustation found on walls, which was represented as a kind of leprosy. The addition of ashes, or alkaline salts, the author either forgot or omitted, because perhaps he did not consider it as indispensably necessary. In another place it is said, Lapis qui dicitur petra solis, or, as it is in other manuscripts, salis; but whether saltpetre is here understood I will not venture to determine. In a third passage we find the words de sale petroso, or de salepetro.
In the works of Bacon the term sal petræ occurs at least three times. According to Casiri, the term pulvis nitratus is to be found in an Arabic manuscript, the author of which lived about the year 1249[1249]. If the work of Geber, already quoted, be genuine, and if this writer lived, as some think, in the eighth century, it would be the oldest where saltpetre is mentioned, in a prescription for an aqua solutiva or dissolutiva, which almost seems to be aqua regia. I have not observed the name sal petræ in the works of Vincent Bellovacensis, who lived in the thirteenth century.
In a word, I am more than ever inclined to accede to the opinion of those who believe that gunpowder was invented in India, and brought by the Saracens from Africa to the Europeans, who however improved the preparation of it, and found out different ways of employing it in war, as well as small arms and cannon[1250]. In no country could saltpetre, and the various uses of it, be more easily discovered than in India, where the soil is so rich in nitrous particles that nothing is necessary but to lixiviate it in order to obtain saltpetre; and where this substance is so abundant, that almost all the gunpowder used in the different wars with which the sovereigns of Europe have tormented mankind was made from Indian saltpetre[1251]. If it be true that saltpetre was not known in Europe till the thirteenth century, neither gunpowder nor aquafortis could have been made before that time; for the former cannot be prepared without saltpetre, nor the latter without nitre. But if it be true that this salt was known at a much earlier period in India, it is not improbable that both gunpowder and aquafortis were used by the Indians and the Arabians before they were employed by the Europeans, especially as the former were the first teachers of chemistry to the latter. In my opinion, what I have already related proves this in regard to gunpowder; and what I shall here add will afford an equal proof in regard to aquafortis.
It is difficult to discover the first mention of mineral acids in the writings of the ancient chemists. In the course of their numerous experiments they obtained indeed, at an early period, acids, the utility of which they extol; but each concealed the process by which they were made; and as they had no method of obtaining them pure, they were for a long time unacquainted with the difference between the kinds. Their prescriptions, when they are found, are so contradictory and so carelessly written, that it is almost impossible to conjecture which of the known acids forms the principal component parts in their recipes or mixtures.
It appears to me, that the first intelligible account of aquafortis occurs in the writings of the Arabians, or of the pupils of Arabian chemists. At present I am acquainted with none older than that to be found in the works of Geber. For though I do not believe that those of which we have Latin translations belong to a Geber of the eighth or ninth century, I am ready to admit that they may be, at any rate, of the twelfth. This appears probable, because about that period aquafortis and various arts are oftener mentioned, and in a much clearer manner, in these writings.
It is to be regretted in the history of chemistry, that it is impossible to determine the period of the Greek chemist or alchemist known under the name of Synesius; but it cannot be doubted that he borrowed a great deal from the works of the Arabians. This Synesius, among the chemical solvents, mentions water of saltpetre, which might be considered as aquafortis[1252]. But, as he mentions at the same time aqua fæcis, he appears to me to allude to the nitrum of the ancients, not to our saltpetre, and in general to strong alkaline leys, which indeed are capable of dissolving many bodies.
The monk Theophilus, of whom I have already spoken, and who in all probability lived in the twelfth century, appears also to have been acquainted with aquafortis; for in some of the passages quoted from his works by Raspe[1253], he speaks of an acid which dissolved all metals. In the writings of Vincent Bellovacensis, in the thirteenth century, some traces, but very doubtful, are found of aquafortis. Where he mentions the different sorts of gold he speaks of dissolving it, but by this expression he does not allude to its treatment with fire, which he speaks of separately[1254]. In another place he mentions the different solvents, and among these names vegetable acids, a water of sal-ammoniac, and a water obtained from alum by distillation. He here means undoubtedly a mineral acid[1255]. Michael Meier, the most learned chemist of the seventeenth century, says that Vincentius speaks of aquafortis as of a secret; but the passage I have not yet been able to find[1256].
Spielman states that Lullius, who died in 1315, in the eightieth year of his age, gave an account of his obtaining aquafortis from saltpetre by the addition of vitriol, and that Basilius Valentin was acquainted with the use of clay for the same purpose. Picus Mirandula however declares it to be uncertain whether Arnoldus de Villa Nova was acquainted with the acid of saltpetre in the fourteenth century.
It appears to be an old tradition that this acid was first employed at Venice, by some Germans, for separating the noble metals, and conveyed thence as an article of merchandize to every part of Europe. The persons who prepared it were there narrowly watched, in order that the process might not become known. They were employed chiefly for separating the gold from the Spanish silver, and by these means acquired great riches. Hence arose the report that the people of Venice understood the art of making gold; and it is certain that in many countries the gold refiners were for a long time considered as gold makers; but in no period were there more gold makers than in that when separation in the moist way became known. I can however give less account of this art of the Venetians than of the introduction of it into France in the fifteenth or the beginning of the sixteenth century.
William Budæus, who was born in 1467, and died in 1540, speaks of it in his book, printed for the first time in 1516, as a thing entirely new at that period[1257]. A man of low extraction, named Le Cointe, first undertook to separate gold from silver at Paris, by means of a water which Budæus calls aqua chrysulca. It is very remarkable, that by means of this water he could separate the smallest particle of gold from silver, and from every other metal; nay, he could even take from vessels their gilding without altering their form. By this art he acquired great wealth; which together with his secret descended to his son, who at the time was the only gold refiner at Paris.