THE VOLATILE PART OF PLAXTS. 117 



has been found, together with asparagin, in beet- juice 

 and in squash seedlings. 



The amides, when heated with water alone, and more 

 easily in presence of strong acids and alkalies, are con- 

 verted into ammonia and the acids from which they are 

 derived. Thus, asparagin yields ammonia and amido- 

 succinic acid at the boiling heat under the influence of 

 hydrochloric acid, or of potassium hydroxide, and gluta- 

 min is broken up by the last-named reagent at common 

 temperatures, and by water alone at the boiling point, 

 with formation of ammonia and amidoglutaric acid. 



The amidoaoids are not decomposed by hot water or 

 acids with separation of ammonia. Amidosuccinic and 

 amidoglutaric acids result from albuminoids by boiling 

 with dilute sulphuric acid, and by the action of bromine. 

 The latter acid as yet has been obtained from vegetable 

 albuminoids only, and is prepared most abundantly from 

 gluten, and especially from mucedin. 



Imides, closely related to the amides, are a series of 

 very interesting substances, into whose chemical consti- 

 tution we cannot enter here further than to say that they 

 contain several NH* groups, i. e., ammonia, NHs, in 

 which two hydrogens, are replaced by hydro-carbon, or 

 oxycarbon groups or carbon atoms. 



These bodies are Uric acidi C5H4N4O8, Adenin, CgHsNo, 

 Guanin, CsHjNbO, Allantoin, C^He'N'iOs, Xanthin, 

 Hypox'antldn, C5H4N4O, Theolromin, C7H8O4O2, Caffein, 

 C8HioN"402, and Vernin, CieHaoNgOg. Of these the 

 first, so far as now known, occurs exclusively in the ani- 

 mal. Adenin, Guanin, Allantoin, Xanthin, and Hypo- 

 xantliin, are common to animals and plants ; the last 

 three are exclusively vegetable. 



Caffein exists in coffee and tea combined with tannic 

 acid. In the pure state it forms white, silky, fibrous 

 crystals, and has a bitter taste. In cofEee it is found to 



* Or its hydro-carbon derivatives, 



