ARABIAN AND MEDIAEVAL SCIENCE. 63 



One interesting case mentioned by Geber of the conversion of a liquid 

 into a solid deserves to be noted here, because nine centuries after- 

 wards the same experiment became almost the starting-point of the 

 fundamental principles of modern chemistry. When quicksilver is 

 maintained with access of air for a considerable length of time at a 

 somewhat high temperature, it is finally converted into a red powder. 

 Geber performed this operation in an open glass vessel with a long 

 neck, and he says that its success depended upon the vessel being 

 left open in order to allow the humidity to escape. The true explana- 

 tion of this experiment had to wait for a discoverer until about a 

 hundred years ago, and the reader will find it again referred to in a 

 subsequent chapter. 



A method of preparing caustic alkali from the ashes of plants is 

 given by Geber, and this method is identical with that still in use, 

 which consists in treating the ashes with quicklime. The true expla- 

 nation of this process also was reserved for a chemist of the seven- 

 teenth century, whose labours are referred to on a subsequent page. 

 Nitric acid, w.hich is one of the most important of Geber's discoveries, 

 he obtained by heating in a retort a mixture of saltpetre, alum, and 

 Cyprus vitriol. The condensed vapour formed that powerful solvent 

 long known under the name of aqua-fortis. Geber found that by the 

 addition to aqua-fortis of sal-ammoniac a still more potent liquid was 

 produced, for it could dissolve gold, a metal which resisted the action 

 of all other acids. This discovery, a's may be imagined, attracted the 

 attention of the alchemists in no small degree. The new solvent was 

 called aqua-regia. and the name is still applied to the mixture of nitric 

 and hydrochloric acids. 



The writings of other Arabian alchemists and chemists are still ex- 

 tant, and although they are not without interest to those who specially 

 cultivate this branch of science, we may here pass them over without 

 further notice. AMAZES (A.D. 860 940), a famous physician of Bagh- 

 dad, must, however, be named as the first authorjo describe the pre- 

 paration of sulphuric acid, which he obtained by distilling green vitriol 

 (sulphate of iron), a process still itsed in preparing the strongest kind 

 of sulphuric acid. This writer also gives the earliest directions for the 

 production of spirits (aqua vita) by distillation, and the production 

 therefrom of alcohol in a still more concentrated state, by another dis- 

 tillation over quicklime. The words alcohol, alkali, alembic, and some 

 other chemical terms, are of Arabian origin, and bear testimony to the 

 past history of the science. The Arabs devoted much attention to 

 the preparation of drugs and medicaments, and many of the prepara- 

 tions which long figured in our pharmacopoeias derived their origin from 

 Arabian sources, as some of their names still indicate. 



While the Arabs were cultivating science and letters with the zeal 

 and intelligence to which the few details we have given above bear 

 testimony, Southern Europe, from which the barbarian incursions 



