214 THE CARBOHYDRATES. 



large colorless six-sided double pyramids or rhomboids with 13.52 per 

 cent NaCl. 



Glucose in neutral or very faintly acid (organic acid) solution under- 

 goes alcoholic fermentation with beer-yeast : CeH^Oe = 2C 2 H 5 .OH+2CO2. 

 In the presence of acid milk or cheese the glucose undergoes lactic-acid 

 fermentation, especially in the presence of a base such as ZnO or CaCOs. 

 The lactic acid may then further undergo butyric-acid fermentation: 



Glucose reduces several metallic oxides, such as copper, bismuth, 

 and mercuric oxide, in alkaline solutions, and the most important 

 reactions for sugar are based on this fact. 1 



TROMMER'S test is based on the property that glucose possesses of 

 reducing cupric hydroxide in alkaline solution into cuprous oxide. Treat 

 the glucose solution with about -J- 1 vol. caustic soda and then carefully 

 add a dilute copper-sulphate solution. The cupric hydroxide is thereby 

 dissolved, forming a beautiful blue solution, and the addition of copper 

 sulphate is continued until a very small amount of hydroxide remains 

 undissolved in the liquid. This is now warmed, and a yellow hydrated 

 suboxide or red suboxide separates even below the boiling temperature. 

 If too little copper salt has been added, the test will be yellowish-brown 

 in color, as in MOORE'S test; but if an excess of copper salt has been added, 

 the excess of hydroxide is converted on boiling into a dark-brown hydrate 

 which interferes with the test. To prevent these difficulties the so- 

 called FEHLING'S solution may be employed. This solution is obtained 

 by mixing just before use equal volumes of an alkaline solution of Rochelle 

 salt and a copper-sulphate solution (173 grams Rochelle salt and about 

 50-60 grams NaOH per liter and 34.65 grams crystalline copper sulphate 

 per liter) . This solution is not reduced or noticeably changed by boiling. 

 The tartrate holds the excess of cupric hydroxide in solution, and an excess 

 of the reagent does not interfere in the performance of the test. In 

 the presence of sugar this solution is reduced. 



According to BENEDICT 2 this test is more delicate if sodium carbonate is 

 used instead of sodium hydroxide in the preparation of FEHLING'S solution. 



BOTTGER-ALMEN'S test is based on the property glucose possesses 

 of reducing bismuth oxide in alkaline solution. The reagent best adapted 

 for this purpose is obtained, according to NYLANDER'S S modification of 

 ALMEN'S original test, by dissolving 4 grams of Rochelle salt in 100 parts 

 of 10 per cent caustic-soda solution and adding 2 grams of bismuth 

 subnitrate and digesting on the water-bath until as much of the bismuth 



1 In regard to the products produced see Neff, Annal. d. Chem. u. Pharm., 357. 



2 Journ. of biol. Chem., 3. 



3 Zeitschr. f. physiol. Chem., 8. 



