162 ELEMENTARY PHYSIOLOGY. [XV. 



5. To a few c.c. of starch mucilage 1 1 p.c. in a 

 test-tube add a drop or two of a moderately 

 strong solution of iodine ; an indigo-blue colour 

 will be produced, if the colour is very dark fill up 

 the test-tube with water. 



G. To 5 c.c. of a 5 p.c. aqueous solution of dextrin 2 

 add a strong solution of iodine drop by drop. 

 A deep brown-red colour will be produced. 

 Warm; the brown-red colour will rapidly dis- 

 appear, a light brownish-yellow tint due to 

 the iodine remaining; on cooling the dextrin 

 colour returns. Now add water ; as the dextrin 

 solution becomes more dilute, the red tint be- 

 comes less obvious, the fluid appears yellow- 

 brown. That this colour is not due to the iodine 

 can be seen by warming the fluid. 



7. To 5 c.c. of a '1 p.c. solution of dextrose (grape- 

 sugar) add an excess of a strong solution of sodium 

 hydrate and a couple of drops of a 1 p.c. solution 

 of cupric sulphate ; the precipitate of hydrated 

 cupric oxide at first formed will dissolve, giving 

 a blue solution. Boil; the cupric oxide will be 

 reduced and a yellow or red precipitate of 



1 To prepare the starch mucilage, take 1 gram of starch, and rub 

 it into a thin paste with cold water. Pour it into a beaker containing 

 one hundred c.c. of boiling water, boil for a few minutes and place it 

 aside to cool. It should have no lumps in it and should be thin 

 enough to be measured out readily with a pipette. 



2 This may be bought at a chemist's or it may be prepared by 

 boiling a little starch with sulphuric acid about 3 p.c., until a drop 

 of the fluid gives a red-brown colour with a drop of iodine. 



