CHAPTER XII. 



CHEMISTRY HISTORICAL AND GENERAL. 



CHEMISTRY is a branch of natural science which has always 

 been of great interest to mankind. There is ample evidence to 

 show that even before historic times men were able to extract 

 several of the useful metals from their ores, knew something of 

 the processes of tanning, dyeing, soap making and glass making; 

 could mix mortar and paints, and do many other things which 

 indicate considerable knowledge of practical chemistry. 



But these ancient people do not seem to have had any knowl- 

 edge of the laws of chemical changes or any definite idea of the 

 chemical elements. In the time of Aristotle, 350 B.C., the four 

 elements were fire, hot and dry, air, hot and wet, earth, cold 

 and dry, and water, cold and wet. The qualities mentioned are 

 physical, not chemical. The elements, according to the Hindoos, 

 were earth, air, fire, water and ether. Among the Chinese they 

 were earth, fire, water, metal and wood; but in no case do the 

 ancients seem to have recognized chemical qualities. 



The first mention of chemistry is found in a dictionary of the 

 llth century, where it is defined as the preparation of silver and 

 gold. In the 16th century Paracelsus says the true use of chem- 

 istry is not to make gold but to prepare medicines. In the works 

 of Glauber (1604-1668) he speaks of various compounds of iron 

 and copper, and of sulphuric, nitric, and hydrochloric acids, but 

 gives no idea of their composition. He also states that salt and 

 mercury are the principles of all metals, and that salt is the 

 origin of all things, and that water and earth have produced all 

 the minerals and metals. 



Georg E. Stahl (1660-1734), whose researches gave rise to a 

 marked advance in chemistry, enumerated four elements, water, 

 acid, earth, and phlogiston. Phlogiston was supposed to be a 

 constituent of all combustible bodies, and it was believed that 



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