THE NATURE OF CHEMICAL PHENOMENA. 
27B 
this last being probably first familiar to the Egyptians. They 
had many of the pigments -which we still employ, could make 
glass, colour it, and form it into beads, &c. ; they employed 
indigo as a dye, understood the use of mordants in dyeing, and, 
in the case of the employment of the famous Tyrian* purple, 
■were more skilled than ourselves in this art. These few ex- 
amples -v^ill serve to indicate that in applied chemistry con- 
siderable progress bad been made. I may add that this more 
particularly applies to the Egyptians, among whom these things 
seem to have been held in high esteem. After this there 
is little recorded till the 8th century, when the Arabian, Geber, 
wrote an account, which shew^s the state of chemistry at his day, 
from which it has been ascertained that the intervening period 
had been one of considerable activity in chemistry as in other 
departments of knowledge. At that time, apparatus for dis- 
tilling, subliming, and calcination, had been devised, also several 
furnaces, which were hardly modified for many centuries after, 
and the sand-bath and w^ater-bath were in use then for mode- 
rating too great heats, as they are to-day. Further, the im- 
portant substances, nitric acid, sulphuric acid, acetic acid, and 
aqua regia had been discovered, and their action on the metals 
studied, whereby many of the commoner salts had become known. 
Still, as these examples indicate, the advance made consisted 
in the invention of new apparatus and processes, and the dis- 
covery of new substances, and the Arabian chemists do not seem 
to have made any great progress in elucidating the nature of the 
phenomena with which they dealt. This may, perhaps, be 
ascribed partly to the alchemistic notions of the time, and 
partly to the circumstance that till a considerable body of facts 
had been established, a prolific and comprehensive theory of 
chemistry, or even a sound classification of chemical bodies, was 
a. matter of vastly greater difficulty than at present. 
From this time till the 16th century, when Paracelsus once 
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