THE MQNOSACCHARIDES. 65 



of carbon atoms as the original substances, while the ketoses give 

 rise to acids which have a smaller number of carbon atoms. The 

 oxyacids which are derived from the aldoses, moreover, are either 

 monobasic or dibasic, according to the extent to which the oxida- 

 tion has been carried. 



These changes are represented by the equations : 



(1) CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO + O = 



Glucose. CH 2 (OH).(CH.OH ) 4 .COOH. 



Gluconic acid. 



(2) CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO + 3O = 



Glucose. COOH.(CH.OH) 4 .COOH + H 2 O. 



Saccharinic acid. 



The acids which can thus be obtained from the aldoses glucose, 

 mannose, and galactose, are the monobasic acids gluconic, man- 

 nonic, and galactonic acid ; and the dibasic acids saccharinic, man- 

 nosaccharinic, and mucinic acid. Of these, saccharinic acid is of 

 special interest, as it can readily be transformed into saccharolactonic 

 acid, which in turn yields glucuronic acid. This latter, as we shall 

 see later, is found also in the animal body. It is an aldehydic acid, 

 and stands midway between gluconic acid and saccharinic acid. It 

 is represented by the formula COOH.CH(OH).CH(OH).CH(OH). 

 CH(OH).COH. 



The hexoses are colorless and odorless substances of a sweetish 

 taste ; they present a neutral reaction, and are readily soluble in 

 water, with difficulty in absolute alcohol, and insoluble in ether. 

 They can be obtained in crystalline form, and diffuse through animal 

 membranes. Some of them are dextrorotatory, others laevorotatory, 

 while still others are optically inactive. They are strong reducing- 

 substances, and for the most part fermentable with yeast. Espe- 

 cially interesting further is the behavior of the hexoses toward the 

 hydrazins in the presence of acetic acid, with which they form 

 hydrazons. These can be further transformed into osazons, which 

 are very characteristic substances, and may serve to distinguish the 

 various sugars from each other. On decomposition with fuming 

 hydrochloric acid the osazons then give rise to the formation of 

 osons i. e., keto-aldehydes, which can be further reduced to ketoses. 

 By starting with an aldose, it is thus possible to obtain an isomeric 

 ketose. These changes may be represented by the equations : 



(1) CH,(OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO + 



Glucose Phenylhydrazin. 



CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CH:N.NH.C 6 H 6 +H 3 



Phenylglucohy drazon . 



(2) CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CH:N.NH.C 6 H 5 + 



C 6 H 5 .NH.NHj = 



CH 2 (OH).CH(OH).CH(OH).CH(OH).C.CH.N.NH.C 6 H 5 -f H 2 O + 2H. 



.NH.C 6 H 6 . 



Phenylglucosazon. 



