27 



^> 



67. Heat another portion of the solution with sulphuric 

 acid ; — it'darkens slowly. If not successful add more dextrose 

 and repeat. 



68. Trommer's test. To another part of the solution 

 add a few drops of a dilute solution of copper sulphate, and 

 afterwards add caustic potash in excess, that is, until the 

 precipitate first formed is re-dissolved and a clear blue fluid 

 is obtained. The hydrated oxide of copper precipitated from 

 the copper sulphate is held in solution in presence of gflucose. 

 Heat slowly turning the tube in the flame. A little below 

 the boiling point, if glucose be present, the blue color disap- 

 pears and a yellow (cuprous hydrate) or red (cuprous oxide) 

 precipitate is obtained. If the upper surface of the fluid has 

 been boiled, the yellow precipitate, when it occurs, contrasts 

 sharply with the deep blue-cOlored stratum below. The pre- 

 cipitate is first yellow, then yellowish 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. 



69. 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 distilled water to make 500 cc. When 

 needed for use 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 efficiency of the solu- 

 tion boil it, and if it remains blue it is good. 



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

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

 oxide) precipitate. 



70. 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. 

 This is known as Boettger's test. Albumin gives the same 



