i6 



glucose. Heal; slowly turning the tube in the flame. A 

 little below the boiling point, if glucose be present, the blue 

 color disappears and a yellow (cuprous hydrate) or red 

 (cuprous oxide) precipitate is obtained. If the upper sur- 

 face of the fluid has been boiled, the yellow precipitate, 

 when it occurs, contrasts .sharply with the deep blue-colored 

 stratum below. The precipitate is first yellow, then yellow- 

 i,sh red, and finally red. It is better seen in reflected than 

 transmitted light. If no sugar be present, only a black 

 color may be obtained. 



51. Fehling's. solution. Solution A. 34.64 grams of pure 

 crystalline copper sulphate are powdered and dissolved in 

 500 cc. of distilled water. Solution B. Sodio-potassium 

 tartrate (Rochelle Salts) 173 grams. Pure caustic potash 

 125 grams. Add enough di.stilled water to make 500 cc. 

 When needed for u.se take equal parts of .solutions A and B. 



The above stock .solutions have been made and each 

 student is to take 30 cc. of each solution. Keep in separate 

 bottles and mix a few cc. of each when ready to make a test. 

 A deep clear blue fluid is the result of the mixture, the 

 Rochelle salt holding the cupric hydrate in solution. If 

 kept too long it is apt to decompose. If in doubt as to the 

 efiiciency of the solution boil it, and if it remains blue it is 

 good. 



Add some of Fehling's solution to a portion of the glu- 

 cose ; boil, a yellowish (cuprous hydrate) or reddish 

 (cuprous oxide) precipitate. 



52. Add to a portion of the glucose solution some strong 

 potassium hydrate solution and then a very small amount of 

 the subnitrate of bismuth. Boil ; a black precipitate results 

 which sometimes forms a mirror on the walls of the test- 

 tube. 



53. The Phenyl-hydrazine Te.st. To about 10 cc. of the 

 glucose solution in a test-tube add 0.2 gram of phenylhy- 

 drazine hydrochlorate, and 0.3 gram of sodium or potassium 



