24 PHYSIOLOGICAL CHEMISTRY 



solution under examination and mix the liquids by gentle shaking. Now heat the 

 upper portion of the mixture to boiling, add an additional i c.c. of the solution and 

 heat the mixture again immediately. The appearance of a blue color accompanied 

 by the precipitation of small particles of indigo blue indicates the presence of dex- 

 trose in the solution under examination. The test will serve to detect the presence 

 of o.i per cent of dextrose. 



7. Precipitation by Alcohol. To 10 c.c. of 95 per cent alcohol add about 2 c.c. 

 of dextrose solution. Compare the result with that obtained under Dextrin, 5, 

 page 48. 



8. Iodine Test. Make the regular iodine test as given under Starch, 5, page 45, 

 and keep this result in mind for comparison with the results obtained later with 

 starch and with dextrin. 



9. Diffusibility of Glucose. Test the diffusibility of glucose solution through 

 animal membrane or parchment paper, making a dialyzer like one of the models 

 shown in Fig. 2. 



FIG. 2. DIALYZING APPARATUS FOR STUDENTS' USE. 



A most satisfactory dialyzing bag may be made of collodion as follows: 

 Pour a solution of collodion into a clean dry Erlenmeyer flask or test-tube. 

 While rotating the vessel on its longitudinal axis, gradually pour out the collodion, 

 at the same time being careful that the interior surface of the flask is completely 

 coated with the solution. Continue the rotation in the inverted position until 

 the collodion ceases to flow. After the solution has evaporated such that the 

 collodion skin on the rim is dry and stiff, cut or loosen it around the edge of the 

 rim. With a pipette or wash bottle run in a few cubic centimeters of water be- 

 tween the membrane and the wall of the flask or test-tube. Shake the inclined 

 vessel while rotating on its longitudinal axis, thus detaching the membrane. 

 Now withdraw the detached bag and fill with water, to determine whether or not 

 it contains defects. 1 



All monosaccharides and disaccharides are diffusible, but many polysac- 

 charides are not. 



10. 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 alkali 

 brings about condensation and decomposition. The brown color is due to the 

 formation of condensation products. Among the decomposition products are the 

 potassium or sodium salts of certain organic acids. 



1 Gies: Quoted by Clark. Bioch. BulL, i, 198, 1911. 



