CHEMISTRY OF THE EIGHTEENTH CENTURY. 343 



FIG. I/O. BOERHAAVE. 



published a treatise on chemistry .which was translated into the prin- 

 cipal languages of Europe, and was long the established text-book in 

 all the medical and other schools where chemistry was systematically 

 studied. Boerhaave was the first to give to the study of the chemistry 

 of animal and vegetable substances such attention as their importance 

 in the economy of nature demands. 



The compounds of magnesia were first distinguished from those 

 of calcium in a treatise published at the beginning of the eighteenth 

 century. FREDERICK HOFFMANN, a German physician of some cele- 

 brity, showed that the well-known Epsom salt did not contain lime, 

 but a kind of alkaline calcareous substance different from lime, united 

 with sulphuric acid. Epsom salts had before this period been called 

 nitre, a term vaguely used by reason of the form of the crystals, or, for 

 distinction, calcareous nitre. When BLACK (p. 286) began to make ex- 

 periments in chemistry, he was desirous of more closely examining the 

 alkaline earth that Hoffmann had described. The results of his ex- 

 periments suggested to him a satisfactory explanation of the action of 

 quicklime on alkaline salts, that is, on potashes, etc. (carbonates) ; and, 



