158 A MANUAL OF BACTERIOLOGY 



GRAVIMETRIC METHOD OF DETERMINATION 

 (DEFREN-O'SULLIVAN) 



For the determination of reducing sugars many prefer the method 

 of Defren and 0' Sullivan, because it is applicable to the determi- 

 nation not only of dextrose but also of maltose and lactose. 1 Mix 

 15 cc. of the copper solution with 15 cc. of the alkaline tartrate in 

 an Erlenmeyer flask, and add 50 cc. of distilled water. Place the 

 flask and its contents in a boiling-water bath and allow them to re- 

 main five minutes. Then run rapidly from a burette into the hot 

 liquor in the flask 25 cc. of the sugar solution to be tested (which 

 should not contain more than ^ per cent of reducing sugar). Allow 

 the flask to remain in the boiling water just fifteen minutes after 

 the addition of the sugar solution, remove, and, with the aid of a 

 vacuum, filter the contents rapidly in a platinum or porcelain Gooch 

 crucible containing a layer of prepared asbestos fiber about 1 cm. thick, 

 the Gooch, with the asbestos, having been previously ignited and 

 weighed. The cuprous oxide precipitate is thoroughly washed with 

 boiling distilled water till the water ceases to be alkaline. 



Dry the Gooch with its contents in the oven, and finally heat to 

 dull redness for fifteen minutes, during which time the red cuprous 

 oxide is converted into the black cupric oxide. If a platinum Gooch 

 is used (and this variety is preferable), it may be heated over the 

 low flame of the burner. If the Gooch is of porcelain, considerable 

 care must be taken to avoid cracking the crucible, the heat being 

 increased cautiously. After oxidation as above, the crucible is trans- 

 ferred to a desiccator, cooled, and quickly weighed. From the mil- 

 ligrams of cupric oxide the milligrams of reducing sugar may be 

 calculated (for a convenient table see Leach, loc. cit. p. 490). 



1 See Leach, Food Inspection and Analysis, New York, 1907. 



