THE URINE. 409 



solution passes into alcoholic fermentation with beer -yeast, 

 C' 6 H 12 6 = 2C 2 H 5 .OH + 2C0 2 . The most favorable temperature 

 for this fermentation is about 25 C. Besides the alcohol and 

 'carbon dioxide there are formed, especially at higher temperatures, 

 small quantities of homologous alcohols (amyl-alcohol), glycerin, and 

 succinic acid. In the presence of acid milk or cheese the grape- 

 sugar passes, especially in the presence of a base such as ZnO or 

 CaC0 3 , into lactic-acid fermentation: C 6 H 12 6 = 2C 3 H 6 3 . (This 

 process is even more complicated and C0 2 is formed thereby, Bou- 

 TROtf, HUEPPE.) The lactic acid may then pass into butyric acid- 

 fermentation : 2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 + 4H. 



Grape-sugar reduces several metallic oxides, such as copper 

 oxide, bismuth oxide, mercuric oxide, in alkaline solutions, and the 

 most important reactions for sugar are based on this fact. 



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

 of reducing copper-hydrated oxide in alkaline solution into sub- 

 oxide. Treat the glucose solution with about -J vol. caustic 

 soda and then carefully add a dilute copper-sulphate solution. 

 The copper-hydrated oxide is thereby dissolved, forming a beautiful 

 blue solution, and the addition of copper sulphate is continued 

 until a very small amount of hydrate remains undissolved in the 

 liquid. This is now warmed and a yellow hydrated suboxide or 

 red suboxide separates even below the boiling-point. 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 hydrate is converted on boiling into a dark-brown 

 hydrate poor in water which interferes with the test. To prevent 

 these difficulties the so-called FEELING'S solution may be em- 

 ployed. This reagent is obtained by mixing before use equal 

 volumes of an alkaline solution of Rochelle salts and a copper- sul- 

 phate solution (see Quantitative Estimation of Sugar in the Urine in 

 regard to concentration). This solution is not reduced or noticeably 

 changed by boiling. The tartrate holds the excess of copper- 

 hydrate oxide 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. 



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

 of reducing bismuth oxide in alkaline solution. The reagent best 



