Isaac Hollandus had stated that mercury could be easily obtained from the salt of lead made by means of distilled vinegar. To prove this he calcined a quantity of acetate of lead, ground the residue to powder, and triturated it with a very strong alkaline lixivium, and kept the lixivium over it covered with paper for months, taking care to add water in proportion as it evaporated. The calx was then distilled in a heat gradually raised to redness; but not a particle of mercury was obtained.[172]
These were not the only laborious experiments which he made with this metal. He distilled it above five hundred times, and found that it underwent no alteration. When long agitated in a glass bottle it is convertible into a black acrid powder, obviously protoxide of mercury. This black powder, when distilled, is converted into running mercury. Exposure of mercury for some months in a heat of 180°, converts it also into protoxide; and if the heat be higher than this, the mercury is converted into a red acrid substance, obviously peroxide of mercury. But this peroxide, by simple distillation, is again reduced into the state of running mercury.[173]
Boerhaave combated the opinions of the iatro-chemists with great eloquence, and with a weight derived from his high reputation, and the extraordinary veneration in which his opinions were held by his disciples. His efforts were assisted by those of Bohn, who combated the medical opinions by arguments drawn both from experience and observation, and perfectly irresistible; and the ruin of the chemical sect was consummated by the exertions of the celebrated Frederick Hoffmann, the founder of the most perfect and satisfactory system of medicine that has ever appeared. His efforts were probably roused into action by a visit which he paid to England in 1683, during which he got acquainted with Boyle and with Sydenham; the former the greatest experimentalist, and the latter the greatest physician of the time; and both of whom were declared enemies to iatro-chemistry.
CHAPTER VI.
OF AGRICOLA AND METALLURGY.
I have been induced by a wish to prosecute the history of the opinions first supported by Paracelsus, and carried so much further by Van Helmont and Sylvius, to give a connected view of their effects upon medical practice and medical theory; and I have come to the commencement of the eighteenth century, without taking notice of one of the most extraordinary men, and one of the greatest promoters of chemistry that ever existed: I mean George Agricola. I shall consecrate the whole of this chapter to his labours, and those of his immediate successors.
George Agricola was born at Glaucha, in Misnia, in the year 1494. When a young man he acquired such a passion for mining and minerals, by frequenting the mountains of Bohemia, that he could not be persuaded to relinquish the study. He settled, indeed, as a physician, at Joachimstal; but his favourite study engrossed so much of his attention, that he succeeded but ill in his medical capacity. This induced him to withdraw to Chemnitz, where he devoted himself to his favourite pursuits. He studied the mineralogical writings of the ancients with the most minute accuracy; but not satisfied with this, he visited the mines in person, examined the processes followed by the miners in extracting the different ores, and in washing and sorting them. He made collections of all the different ores, and studied their nature and properties attentively: he likewise collected information about the methods of smelting them, and extracting from them the metals in a state of purity. The information which he collected, respecting the mines wrought in the different countries of Europe, is quite wonderful, if we consider the period in which he lived, the little intercourse which existed between nations, and the total want of all those newspapers and journals which now carry every new scientific fact with such rapidity to every part of the world.
Agricola died at Chemnitz in the year 1555, after he had reached the sixty-first year of his age. Maurice, the celebrated Elector of Saxony, settled on him a pension, the whole of which he devoted to his metallurgic pursuits. To him we find him dedicating the edition of his works which he published in the year of his death, and which is dated the fourteenth before the calends of April, 1555. He even spent a considerable proportion of his own estate in following out his favourite investigations. In the earlier part of his life he had expressed himself rather favourable to the protestant opinions; but in his latter days he had attacked the reformed religion. This rendered him so odious to the Lutherans, at that time predominant in Chemnitz, that they suffered his body to remain unburied for five days together; so that it was necessary to remove it from Chemnitz to Zeitz, where it was interred in the principal church.
His great work is his treatise De Re Metallica, in twelve books. In this work he gives an account of the instruments and machines, and every thing connected with mining and metallurgy; and even gives figures of all the different pieces of apparatus employed in his time. He has also exhibited the Latin and German names for all these different utensils. This work may be considered as a very complete treatise on metallurgy, as it existed in the sixteenth century. The first six books are occupied with an account of mining and smelting. In the seventh book he treats of docimasy, or the method of determining the quantity of metal which can be extracted from every particular ore. This he does so completely, that most of his processes are still followed by miners and smelters. He gives a minute and accurate account of the furnaces, muffles, crucibles, &c., almost such as are still employed, with minute directions for preparing the ores which are to be subjected to examination, the fluxes with which they must be mixed, and the precautions necessary in order to obtain a satisfactory result. In short, this book may be considered as a complete manual of docimasy. How much of the methods given originated with Agricola it is impossible to say. He probably did little more than collect the scattered processes employed by the smelters of metals, in different parts of the world, and reduce the whole to a regular system. But this was a great deal. Perhaps it is not saying too much, that the great progress made in the chemical investigation of the metals, was owing in a great measure to the labours of Agricola. Certainly the progress made by the moderns, in the difficult arts of mining and metallurgy, must in a great measure be ascribed to the labours of Agricola.
In the eighth book he describes the mechanical preparation of the ores, and the mode of roasting them, either in the open air or in furnaces. The ninth book is occupied with an account of smelting-furnaces. It contains also a description of the processes for obtaining mercury, antimony, and bismuth, from their ores. The tenth book treats of the separation of silver and gold from each other, by means of nitric acid and aqua regia: minute directions for the preparation of which are given. The modes of purifying the precious metals by means of sulphur, antimony, and cementations, are also described. In the eleventh book he treats of the method of purifying silver from copper and iron, by means of lead. He gives an account also of the processes employed for smelting and purifying copper. In the twelfth book he treats of the methods of preparing common salt, saltpetre, alum, and green vitriol, or sulphate of iron: of the preparation and purification of sulphur, and of the mode of manufacturing glass. In short, Agricola’s work De Re Metallica is beyond comparison the most valuable chemical work which the sixteenth century produced, and places the author very high indeed among the list of the improvers of chemistry.