Page:The American Cyclopædia (1879) Volume IV.djvu/366

358 CHEMISTRY of the metals was considered to depend upon the fixity of these ingredients ; their color upon the relative amount of sulphur which they con- tained. The author of this theory is unknown. It is fully developed in the writings of the Arab Geber, who refers it to the ancients. It experienced but slight alteration till toward the end of the alchemical period, when the idea of salt was added to those of mercury and sulphur. Among the Arabs, physicians were the principal chemists, many of them being highly scientific men. The writings of Geber, in the latter half of the 8th century, indicate the amount of chemical knowledge which they then possessed. He describes the metals very accurately, and mentions the different degrees of affinity which mercury has for gold, silver, lead, tin, and copper. He knew how to con- vert metals into oxides by means of heat, and how to purify native sulphur by solution in al- kaline lye, and reprecipitation by vinegar. Sev- eral metallic sulphides were also known to him, as well as the fact that metals increase in weight and change color when heated with sulphur. The Arabs, unlike some of their predecessors, did not consider simple change of color in a metal to be transmutation. They demanded an entire change of its properties that it should be made like some other metal. Trans- mutation was regarded by them in the light of a scientific problem as yet unsolved. Their knowledge of salts was comparatively exten- sive, alum, saltpetre, sal ammoniac, and green vitriol being accurately described. The car- bonates of the fixed alkalies, and the use of lime to render them caustic ; the preparation of sulphuric acid by the distillation of alum ; of nitric acid by the distillation of saltpetre and green vitriol ; the preparation of strong acetic acid from vinegar, and of aqua regia from nitric acid and sal ammoniac, are all described by Geber. By means of the acids thus obtained, artificial salts were prepared, as nitrate of sil- ver and bichloride of mercury ; gold was also dissolved. They purified their preparations by distillation, by recrystallization, and by sublima- tion. The purification of the noble metals by cupellation, the use of the water bath, and pro- cesses of filtration, were also known. Several words still in common use, as alkali, alcohol, &c., originated with them. Geber himself published a special work on the construction of chemical furnaces. The importance of the Arabs as chemists ceased with the 12th century; not, however, before they had awakened in other nations an enthusiasm for the science. During the 18th century it had spread oter the greater part of northwestern Europe. The views of Albertus Magnus, who flourished in Germany during the 13th century, will serve as in exam- ple of those of his day. Believing fully in the transmutation of metals, he considered it easier to convert them into each other when their properties are analogous. Thus gold can be more readily made from silver than from any other metal, for the mixture of which it is com- posed is very similar to that which forms silver. Indeed, it would only be necessary to change the color and weight of the latter, in order to obtain gold. He admits that different species of bodies cannot be converted one into the other. The metals, however, he regarded as mere varieties of one and the same species, being all composed alike. His views concern- ing this composition are essentially the same as those of Geber, but he believed that, besides sulphur and mercury, the metals must contain water, to the cold of which their solidity is due, seemingly mingling a portion of Aristotle's doctrine with that of Geber. The knowledge of practical chemistry detailed in his works is in advance of that possessed by Geber. For example, he describes the separation of sil- ver from gold by means of nitric acid ; a method of preparing metallic arsenic ; and ob- served that sulphur attacks all metals, except gold, when heated with them. Contemporary with Albertus lived Roger Bacon, a most able diffuser and promoter of chemical science. At the same time, Raymond Lully made many new and important observations, but introduced an obscure style of writing, and fell into many absurdities, like those which soon became char- acteristic of alchemy. The transmutation of metals was now no longer spoken of as a pos- sibility, but as a well established fact. In the 14th century alchemy had become diffused over the greater part of the civilized world. It was, however, especially among the priesthood that its followers were to be found, in spite of its pro- hibition by a bull of Pope John XXII. in 1817. In the latter part of the 15th century flour- ished Basil Valentine. In addition to the ele- ments, sulphur and mercury, of the earlier al- chemists, he mentions salt. From these three substances he supposes that not only metals but all substances are composed. He first clearly described bismuth and zinc ; prepared antimony and several new salts ; also muriatic acid, by distilling common salt with green vitriol. He knew how to precipitate copper from its solu- tions by means of iron, also gold by means of mercury, and had much general knowledge of precipitation. With him qualitative analysis first appears. He detected iron in many speci- mens of hard tin, copper in the brittle iron of Hungary, and silver in the copper from Mans- feld. He explains how a similar occurrence of the noble metals in the base metals of commerce may have given rise to many of the so-called transmutations of false alchemists. The great impulse given to all branches of learning by the remarkable events of the 15th century had its effect on chemistry. The overthrow of the Byzantine empire, which scattered many of its learned men over western Europe, the inven- tion of printing, and, above all, the growing tendency of men to think for themselves, were of peculiar importance to it. The implicit con- fidence hitherto placed in noted authorities be- gan to diminish, and their theories to be ques- tioned. The ground was made ready for a new