12 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



boiling, the solution turns yellow, then brown, and develops 

 .the odor of caramel, especially after acidifying with dilute 

 sulphuric acid. 



4. Bismuth Test. Saturate some of the solution at the 

 boiling-point with solid sodium carbonate, add a little bis- 

 muth subnitrate, heat to boiling, and keep boiling for some 

 time: gray or black color due to the formation of finely 

 divided metallic bismuth. This reaction may also be per- 

 formed with sodium hydroxide instead of sodium carbonate, 

 using only a very slight amount of caustic soda, but the 

 simultaneous action of the alkali on the milk-sugar cannot 

 be excluded and the color is then a dirty grayish green. 



5. To a few cubic centimeters of the solution add some 

 sodium carbonate solution and a little freshly prepared 

 potassium ferricyanide solution. Decolorization on warm- 

 ing, due to the formation of ferrocyanide of potassium. 



6. To some of the solution add silver nitrate solution and 

 ammonia and warm. Separation of metallic silver in the 

 form of a bright mirror or a gray powder. A very pretty 

 mirror is obtained if we use an excess of caustic soda with 

 only a little ammonia in the reaction (caution on account of 

 the possible formation of fulminating silver). Cane-sugar 

 and mannite also give the reaction under these conditions, 

 but not with ammonia and silver nitrate. 



7. Indigo Test. Use only the weaker solution of the 

 milk-sugar in this test. To a small portion of the sugar 

 solution add some freshly prepared solution of indigo carmine 

 or sodium indigo sulphonate until a blue color is produced, 

 make alkaline with a few drops of sodium carbonate solution, 

 and warm. The solution turns first violet, then red, then 

 yellow, and finally becomes almost colorless. The reaction 

 depends on the reduction of indigo blue to indigo white. 

 Pour half of the solution into another test-tube and shake 

 thoroughly with air. It turns blue again: oxidation of the 



