196 MODERN SCIENCE READER 



denote the art in which that substance was employed, the 

 substance itself (the philosopher's stone) retaining only 

 the name al-iksir. 



THE BRANCHES OP CHEMISTRY. The facts of chemistry 

 have been grouped in a variety of ways, either in the inter- 

 ests of research or according to their usefulness in connec- 

 tion with kindred sciences or with the arts hence such 

 titles as Animal, Vegetable, Medical, Astronomical, Metal- 

 lurgical Chemistry, etc., which in a general way explain 

 themselves. Chemistry proper may be considered as com- 

 prising the following four branches : analytical, descriptive, 

 general and applied. Analytical chemistry may be defined 

 as the art of determining the composition of substances; 

 under the names of technical analysis, physiological anal- 

 ysis, etc., many of its methods form an important part of 

 applied chemistry. Descriptive chemistry deals with the 

 chemical and physical characteristics of substances; it 

 forms a record of the properties of substances, which are 

 arranged, for convenience of reference or for didactic pur- 

 poses, in accordance with the principles of general chem- 

 istry. The two great subdivisions of descriptive chemistry 

 are inorganic and organic chemistry; the latter dealing 

 with the compounds of carbon, the former with those of all 

 the other elements. General chemistry includes theoretical 

 and physical chemistry, which are usually treated together. 

 Theoretical chemistry comprises the laws of the composition 

 and chemical behavior of compounds; physical chemistry 

 treats of the physical properties of compounds, of homo- 

 geneous mixtures, and of the physical phenomena (thermal, 

 electrical, etc.) accompanying the transformations of sub- 

 stances in general. Applied chemistry comprises all the 

 facts and methods of chemistry that find practical employ- 

 ment. The most important subdivisions of this branch are : 

 (1) Biological chemistry, including the facts connected 

 with physiological and pathological phenomena in animals 

 and plants; (2) Agricultural chemistry, which deals with 

 the problems of rural economy; and (3) Industrial, Tech- 



