Lead, in Geber’s opinion, differs from tin only in having a more unclean substance commixed of the two more gross substances, sulphur and mercury. The sulphur in it is burning and more adhesive to the substance of its own mercury, and it has more of the substance of fixed sulphur in its composition than tin has.117
Such are the opinions which Geber entertained respecting the composition of the metals. I have been induced to state them as nearly in his own words as possible, and to give the reasons which he has assigned for them, even when his facts were not quite correct, because I thought that this was the most likely way of conveying to the reader an accurate notion of the sentiments of this father of the alchymists, upon the very foundation of the whole doctrine of the transmutation of metals. He was of opinion that all the imperfect metals might be transformed into gold and silver, by altering the proportions of the mercury and sulphur of which they are composed, and by changing the nature of the mercury and sulphur so as to make them the same with the mercury and sulphur which constitute gold and silver. The substance capable of producing these important changes he calls sometimes the philosopher’s stone, but generally the medicine. He gives the method of preparing this important magistery, as he calls it. But it is not worth while to state his process, because he leaves out several particulars, in order to prevent the foolish from reaping any benefit from his writings, while at the same time those readers who possess the proper degree of sagacity will be able, by studying the different parts of his writings, to divine the nature of the steps which he omits, and thus profit by his researches and explanations. But it will be worth while to notice the most important of his processes, because this will enable us to judge of the state of chemistry in his time.
4. In his book on furnaces, he gives a description of a furnace proper for calcining metals, and from the fourteenth chapter of the fourth part of the first book of his Sum of Perfection, it is obvious that the method of calcining or oxidizing iron, copper, tin, and lead, and also mercury and arsenic were familiarly known to him.
He gives a description of a furnace for distilling, and a pretty minute account of the glass or stoneware, or metallic aludel and alembic, by means of which the process was conducted. He was in the habit of distilling by surrounding his aludel with hot ashes, to prevent it from being broken. He was acquainted also with the water-bath. These processes were familiar to him. The description of the distillation of many bodies occurs in his work; but there is not the least evidence that he was acquainted with ardent spirits. The term spirit occurs frequently in his writings, but it was applied to volatile bodies in general, and in particular to sulphur and white arsenic, which he considered as substances very similar in their properties. Mercury also he considered as a spirit.
The method of distilling per descensum, as is practised in the smelting of zinc, was also known to him. He describes an apparatus for the purpose, and gives several examples of such distillations in his writings.
He gives also a description of a furnace for melting metals, and mentions the vessels in which such processes were conducted. He was acquainted with crucibles; and even describes the mode of making cupels, nearly similar to those used at present. The process of cupellating gold and silver, and purifying them by means of lead, is given by him pretty minutely and accurately: he calls it cineritium, or at least that is the term used by his Latin translator.
He was in the habit of dissolving salts in water and acetic acid, and even the metals in different menstrua. Of these menstrua he nowhere gives any account; but from our knowledge of the properties of the different metals, and from some processes which he notices, it is easy to perceive what his solvents must have been; namely, the mineral acids which were known to him, and to which there is no allusion whatever in any preceding writer that I have had an opportunity of consulting. Whether Geber was the discoverer of these acids cannot be known, as he nowhere claims the discovery: indeed his object was to slur over these acids, as much as possible, that their existence, or at least their remarkable properties, might not be suspected by the uninitiated. It was this affectation of secrecy and mystery that has deprived the earliest chemists of that credit and reputation to which they would have been justly entitled, had their discoveries been made known to the public in a plain and intelligible manner.
The mode of purifying liquids by filtration, and of separating precipitates from liquids by the same means, was known to Geber. He called the process distillation through a filter.
Thus the greater number of chemical processes, such as they were practised almost to the end of the eighteenth century, were known to Geber. If we compare his works with those of Dioscorides and Pliny, we shall perceive the great progress which chemistry or rather pharmacy had made. It is more than probable that these improvements were made by the Arabian physicians, or at least by the physicians who filled the chairs in the medical schools, which were under the protection of the califs: for as no notice is taken of these processes by any of the Greek or Roman writers that have come down to us, and as we find them minutely described by the earliest chemical writers among the Arabians, we have no other alternative than to admit that they originated in the east.
I shall now state the different chemical substances or preparations which were known to Geber, or which he describes the method of preparing in his works.
1. Common salt. This substance occurring in such abundance in the earth, and being indispensable as a seasoner of food, was known from the earliest ages. But Geber describes the method which he adopted to free it from impurities. It was exposed to a red heat, then dissolved in water, filtered, crystallized by evaporation, and the crystals being exposed to a red heat, were put into a close vessel, and kept for use.118 Whether the identity of sal-gem (native salt) and common salt was known to Geber is nowhere said. Probably not, as he gives separate directions for purifying each.
2. Geber gives an account of the two fixed alkalies, potash and soda, and gives processes for obtaining them. Potash was obtained by burning cream of tartar in a crucible, dissolving the residue in water, filtering the solution, and evaporating to dryness.119 This would yield a pure carbonate of potash.
Carbonate of soda he calls sagimen vitri, and salt of soda. He mentions plants which yield it when burnt, points out the method of purifying it, and even describes the method of rendering it caustic by means of quicklime.120
3. Saltpetre, or nitrate of potash, was known to him; and Geber is the first writer in whom we find an account of this salt. Nothing is said respecting its origin; but there can be little doubt that it came from India, where it was collected, and known long before Europeans were acquainted with it. The knowledge of this salt was probably one great cause of the superiority of the Arabians over Europeans in chemical knowledge; for it enabled them to procure nitric acid, by means of which they dissolved all the metals known in their time, and thus acquired a knowledge of various important saline compounds, which were of considerable importance.
There is a process for preparing saltpetre artificially, in several of the Latin copies of Geber, though it does not appear in our English translation. The method was to dissolve sagimen vitri, or carbonate of soda, in aqua fortis, to filter and crystallize by evaporation.121 If this process be genuine, it is obvious that Geber must have been acquainted with nitrate of soda; but I have some doubts about the genuineness of the passage, because the term aqua fortis occurs in it. Now this term occurs nowhere else in Geber’s work: even when he gives the process for procuring nitric acid, he calls it simply water; but observes, that it