152 SOIL BACTERIOLOGY 



4. Place the flask at once over the flame and boil for one 

 minute after violent bubbling starts. 



5. Now place a strip of lead acetate paper moistened with 

 not more than 3 drops of water over the mouth of the flask. 



6. Boil for two minutes, remove, and dry the paper. 



7. Compare the paper with standard color chart. 



Truog, E., Bui. 249, Wis. Agr. Exp. Sta., 1915. 



(n) Reducing Sugars (Defren-O'Sullivan) : 



1. Mix 15 c.c. of Fehling's copper solution (see p. 138) 

 (a) with 15 c.c. of the alkaline tartrate solution (b) in a 

 300-c.c. Erlenmeyer flask, and add 50 c.c. of distilled 

 water. 



2. Place the flask and its contents in a water-bath 

 containing boiling water and allow it to remain five minutes. 



3. Then run rapidly from a buret into the hot liquor in 

 the flask 25 c.c. of the sugar solution to be tested, which 

 should contain not more than | per cent, of reducing sugar. 



4. 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 through a porcelain Gooch crucible containing a 

 layer of prepared asbestos fiber about inch thick, the 

 Gooch, with the asbestos, having been previously ignited, 

 cooled, and weighed. 



5. The cuprous oxid precipitate is washed thoroughly 

 with boiling distilled water until the water ceases to be 

 alkaline. The asbestos used should be of the long-fibered 

 variety and should be especially prepared as follows: Boil 

 first with nitric acid (sp. gr. 1.05-1.10), washing out with 

 hot water; then boil with a 25 per cent, solution of sodium 

 hydroxid; and finally wash out the alkali with hot water. 

 Keep the asbestos in a wide-mouthed bottle and transfer 



