594 CONSIDERATION OF CARBON COMPOUNDS. 



intensely green by various oxidizing agents, such as ferric chloride and others. 

 Some of the salts of thalline, chiefly the sulphate, tartrate, and tannate, have 

 been used medicinally. 



51. TERPENES AND THEIR DERIVATIVES. 



The group of hydrocarbons of the general formula (C 5 H 8 ) X , found 

 largely in the volatile oils, has been called by the generic word ter- 

 penes, but this term has been more specifically applied to the sub- 

 group C 10 H 16 . According to the molecular complexity this group has 

 been classified into : 



Hemiterpenes C 5 H 8 , 



Terpenes proper Ci H l6 , 



Sesquiterpenes C 15 H 24 , 



Diterpenes C 20 H 32 , 



Polyterpenes (C 10 H 16 ) X . 



Isopene is the only representative of the hemiterpenes found in a 

 volatile oil, and does not occur naturally, but is formed by the de- 

 structive distillation of rubber or gutta percha. The terpenes proper 

 and sesquiterpenes are among the principal constituents of the vola- 

 tile oils. The diterpenes and higher polyterpenes are more rarely 

 found and but little studied. 



Volatile or essential oils. The term essential oil is more a phar- 

 maceutical than chemical term, and is used for a large number of 



QUESTIONS. What is the difference between fatty and aromatic compounds, 

 and from which two hydrocarbons are they derived ? From what source is 

 benzene obtained, how can it be made from benzoic acid, and what are its 

 properties ? Give the graphic formulas of benzene, nitro-benzene, phenol, 

 thymol, benzoic acid, and salicylic acid. Mention methane derivatives which 

 have a constitution analogous to that of the substances mentioned. Give com- 

 position, properties, and mode of manufacture of, and tests for carbolic acid. 

 What relation exists between benzoic acid and oil of bitter almond? What is 

 the source of amygdalin, to which class of substances does it belong, and what 

 are the products of its decomposition under the influence of emulsin ? Explain 

 the process for the manufacture of salicylic acid, and state its properties. 

 Give composition and properties of naphthalene and naphthol. Give tests for 

 tannin, state the source from which it is derived and for what it is used. From 

 what, and by what process, is aniline obtained; what is its composition and 

 what its constitution? How are aniline dyes manufactured from aniline? 

 State the properties and some reactions characteristic of antipyrine. What 

 is saccharin, and what are its properties ? State the composition of iodol. 



