26 PHYSIOLOGICAL CHEMISTRY. 



solution through animal membrane, or parchment paper, making 

 a dialyzer like one of the models shown in Fig. i, p. 25. 



8. Moore's Test. To 2-3 c.c. of sugar solution in a test-tube 

 add an equal volume of concentrated KOH or NaOH, and boil. 

 The solution darkens and finally assumes a brown color. At this 

 point the odor of caramel may be detected. This is an exceedingly 

 crude test and is of little practical value. The brown color is due to 

 the oxidation of the dextrose and the resulting formation of the 

 potassium or sodium salts of certain organic acids which are formed 

 as oxidation products. 



9. Reduction Tests. To their aldehyde or ketone structure 

 many sugars owe the property of readily reducing alkaline solu- 

 tions of the oxides of metals like copper, bismuth and mercury; 

 they also possess the property of reducing ammoniacal silver solu- 

 tions with the separation of metallic silver. Upon this property 

 of reduction the most widely used tests for sugars are based. When 

 whitish-blue cupric hydroxide in suspension in an alkaline liquid 

 is heated it is converted into insoluble black cupric oxide, but if a 

 reducing agent like certain sugars be present the cupric hydroxide 

 is reduced to insoluble yellow cuprous hydroxide, which in turn, 

 on further heating, may be converted into brownish-red or red 

 cuprous oxide. These changes are indicated as follows : 



OH 

 / 

 Cu 



Nw Cupric oxide 



OH 



Cupric hydroxide 

 (whitish-blue). 



OH 



/ 

 Cu 

 \ 

 OH 



^* 2Cu - OH + H 2 = 0. 



OTT Cuprous hydroxide 



,, V (yellow). 



Cu 

 \ 

 OH 



