ORGANIC CHEMISTRY 17 



precipitation of an insoluble compound with digitonin.* 

 Certain colour reactions are characteristic, f such as a red 

 colour given by its solution in chloroform on the addition 

 of concentrated sulphuric acid. 



Ring compounds which contain other elements in the ring 

 nucleus in addition to carbon are called heterocyclic com- 

 pounds. The pyrrol group consisting of four carbon atoms 

 and one nitrogen occurs in several important compounds. 



Several benzene nuclei or benzene nuclei and heterocyclic 

 rings may occur united in various degrees, for example the 

 in dole group occurs in tryptophane. 



HC CH CH 



/\ 



HC CH CH 



HC CH 



HC CH CH 

 NX NX 

 CH NH 



Pyrrole. Indole. 



COMPOUNDS CONTAINING NITROGEN 



The nitrogenous compounds of biological interest are 

 mainly derivates of ammonia. On replacing the hydrogen 

 atoms of ammonia (NH 3 ) by other groups substituted am- 

 monias are formed. 



If one of the hydrogen atoms is replaced by a group so that 

 the nitrogen is linked directly to the carbon the compound is 

 called an amine, but if the nitrogen and carbon are united, 

 through the intermediation of an oxygen atom, the compound 

 is called an amide. 



NH, R NH 2 RCONH 2 



Ammonia. Amine. Amide. 



These two types of substances differ in their reactions. The 

 latter yields ammonia on treatment with either acid or alkali 

 whilst the former is not decomposed by such treatment. 



Amines are basic and form salts with acids. 



Compounds consisting of a sugar and an amine are occa- 

 sionally found : the simplest of which is the amine of glucose, 

 glucosamine. Other basic nitrogen compounds have been 

 mentioned under the heading of the fats as forming part of 

 the phosphorised fats. 



* A. Windhaus, Zeit. f. physiol. Ghent., 1910, vol. 65, p. no. 

 f E. Salkowski, Zeit. f. physiol. Chem., 1908, vol. 57, p. 523. 

 2 



