CARBOHYDRATES 113 



ary proteoses (deutero-proteoses) are precipitated. The peptones remain 

 in solution. Try the biuret test on the precipitate and on the nitrate con- 

 taining the peptone, in the latter instance making the solution strongly alka- 

 line with solid sodium or potassium hydroxide. 



d. From what you have learned of the properties of the derived proteins 

 in the text and in the laboratory, prepare a chart (Exp. 5) in which the 

 properties of these substances are indicated. Compare the results in this 

 chart and the results in this table with the similar one that you made for 

 the albumins and globulins. 



CARBOHYDRATES. 



12. Starch. a. Examine under the microscope and sketch the starch 

 granules obtained by grinding some potato scrapings in a mortar with a 

 little water; examine and sketch also the granules of corn, wheat (flour), 

 and arrowroot starch. 



b. Starch Paste. Make a suspension of i gram of arrowroot starch in a 

 little distilled water by grinding in a mortar, and pour slowly into some 

 boiling water. Heat for a few minutes longer, cool and make up to 

 100 c.c. 



c. Iodine Test. Shake up three or four drops of dilute iodine solution 

 with 2 c.c. starch. A deep blue color appears. The color is discharged in 

 dilute alkali and reappears on acidifying again. Heat also discharges 

 the color. 



d. Fehling's Test. Fill a test-tube about a fourth full of Fehling's 

 solution and heat to boiling for a minute or two. Add a few drops of starch 

 paste. The red precipitate of copper (cuprous) oxide should not be obtained, 

 for pure starch does not reduce Fehling's solution. 



e. Hydrolysis of Starch. Boil starch solution with 5 per cent, sulphuric 

 acid for fifteen minutes. Test with Fehling's solution, first neutralising the 

 excess of acid. A copious precipitate of cuprous oxide sho\vs that the starch 

 has been converted to reducing sugar. 



13. Dextrins. Make a 5 per cent, solution of dextrin in distilled water 

 and try: 



a. Iodine Test. This gives a red which is characteristic. 



b. Fehling's Test. 



. 14. Dextrose. Test a 5 per cent, solution of dextrose: 



a. Iodine Test. No reaction. 



b. Fehling's Test. 



15. Glycogen. Use i per cent, solution of glycogen. Note the char- 

 acteristic opalescence of the solution. 



a. Iodine Test. A wine-red, somewhat like that given by dextrin. 



b. Fehling's Test. Glycogen does not reduce the copper solution. 



c. Hydrolysis. Test as in e. The glycogen is hydrolyzed to dextrose. 



