52 Estimations occurring in Agricultural Analysis [81, 82 



these together in about 300 c.c. of water. Decant into a 

 500-c.c. flask, and make up to the 500-c.c. mark. Bottle and 

 label ' Fehling's solution II.' ' 



81. Preparation of Sugar Solution.— Weigh out 

 exactly 2*375 grams of pure crystallised cane sugar. Dissolve 

 in about 50 c.c. of water in a beaker, add 2 c.c. of dilute HC1, 

 and place the beaker on the water bath for twenty minutes. 

 This will convert the cane sugar entirely into glucose. Just 

 neutralise with caustic soda, decant into a 500-c.c. flask, and 

 wash the beaker, pouring the washings into the flask. Make 

 up to 500 c.c. and mix well. If this solution has been 

 correctly made, 10 c.c. will contain '05 gram of glucose, which 

 is equivalent to '0475 °f cane sugar. 



82. Standardisation of Fehling's Solution.— For 

 this purpose the sugar solution just prepared may be considered 

 accurate. In fact, for the reasons set forth in article 79 it is 

 far more likely to be accurate than the Fehling's solution. 

 Fill two burettes, one with sugar solution and the other with 

 Fehling's solution I. Place the burettes in clamps which 

 support them at such a height that their taps are about 

 8 inches above the bench. Run 5 c.c. of solution I. into an 

 evaporating basin 4 inches in diameter. With a pipette add 

 5 c.c. of solution II. Stir with a glass rod until the solution 

 becomes quite clear, then place the basin on a tripod and 

 heat it just to boiling. It is most convenient to have a 

 Bunsen burner about a foot away from the burette containing 

 the sugar solution. This enables the operator to slide the 

 tripod with the basin either under the burette or over the 

 burner. When the solution boils, slide it under the burette 



1 Fehling's solution II., like all other strong solutions of potash and 

 soda, is apt to give trouble by fixing the stopper of the bottle tightly. 

 This difficulty may be overcome by rubbing the stopper lightly with 

 vaseline. 



