CARBOHYDRATES. 539 



nated and cellulose reformed by the action of alkalies, of concentrated 

 sulphuric acid, and by reducing agents. Treated with a solution of 

 a ferrous salt in hydrochloric acid, they decompose just as any 

 nitrate, liberating nitric oxide gas. 



Glycog-en (C 6 H 10 O 5 ) X . Found exclusively in animals ; it occurs in 

 the liver, the white blood-corpuscles, in many embryonic tissues, and 

 in muscular tissue. Pure glycogen is a white, starch-like, amorphous 

 substance, insoluble in alcohol. It forms an opalescent solution with 

 water, gives a red color with iodine, and by hydrolysis is converted 

 into glucose. 



Glucosides. This term is applied to a group of substances (chiefly 

 of vegetable origin) which, by the action of dilute acids or enzymes, 

 are decomposed with the production of a sugar, and one or two other 

 substances not carbohydrates. To this class of bodies belong amyg- 

 dalin, digitalin, indican, myronic acid, salicin, etc. Some of these 

 compounds will be considered later on. 



49. COMPOUNDS CONTAINING NITROGEN. 

 Organic compounds may contain nitrogen in three forms, viz., as 

 nitric (or nitrous) acid, ammonia, cyanogen, or derivatives of these 

 compounds. 



Derivatives of nitric acid. 



Organic compounds containing nitrogen in the nitric acid form do 

 not occur in nature, but are obtained exclusively by artificial means, 

 often by treatment of the organic substance with concentrated nitric 

 acid. Many of these compounds are highly combustible or more or 

 less explosive, as, for instance, cellulose trinitrate, mercuric fulminate, 

 and others. 



QUESTIONS. To which group of substances is the term " carbohydrates " 

 applied ? State the general properties of carbohydrates. Mention the three 

 groups of carbohydrates, and the composition and characteristics of the mem- 

 bers of each group. Mention some fruits in which grape-sugar, and some 

 plants in which cane-sugar is found. What is the difference between grape- 

 sugar and cane-sugar, and by what tests can they be distinguished ? From 

 what source, and by what process, is milk-sugar obtained ? What is starch, 

 what are its properties, by what tests can it be recognized, and what substance 

 is formed when diastase or dilute acids act upon it ? Where is cellulose found 

 in nature, and what are its properties? What compounds may be obtained by 

 the action of nitric acid upon cellulose, and what are they used for? What 

 substances are termed glucosides ? Mention some of the more important glu- 

 cosides. 



