14 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



ceasing the color. Glucose solution (2 per cent.), when treated in 

 the same way, though it does not become milky at first, also yields a 

 red color and more quickly than the milk-sugar; the precipitate, how- 

 ever, soon becomes yellow. If more ammonia be added (2 cc.) there 

 will be formed at first a very beautiful cherry-red color, which, how- 

 ever, also disappears very quickly. 



2. The Formation of Mucic Acid, C 6 Hi 8 . Five grams of milk-sugar 

 are put into a flask with 15 cc. of nitric acid of specific gravity 1.2, and 

 5 cc. of nitric acid of about 1.48 specific gravity, 1 and the mixture is 

 cautiously heated until the beginning of a violent reaction (strong 

 evolution of oxides of nitrogen). Remove the flame at once and let 

 stand till next day. Pour off the nitric acid from the crystallized 

 mucic acid, wash with water, first by decantation, then on the filter, 

 and let it dry on filter-paper. To identify the substance dissolve a 

 portion of the mucic acid in an excess of ammonia, evaporate the 

 solution to dryness on the water-bath, and heat the dry residue in a 

 dry test-tube: pyrrol, C 4 H 4 NH, is formed. The vapor colors a pine 

 splinter, moistened with strong hydrochloric acid and held in the 

 mouth of the tube, a deep-red. If we treat glucose in the same way 

 with nitric acid nothing separates. The solution contains a con- 

 siderable quantity of oxalic acid, but no mucic acid. 



3. The Conduct of Milk-sugar on Heating with Hydrochloric Acid. 

 Dissolve about 6 g. of commercially pure milk-sugar in 125 cc. of 

 water by heating to boiling, let cool, and determine how much this 

 solution rotates the plane of polarized light. To 100 cc. of this solu- 

 tion in a flask add 10 cc. of hydrochloric acid and heat for half an 

 hour; -nearly neutralize the solution with dilute caustic soda (com- 

 plete neutralization would make the color of the solution too dark), 

 let cool, pour into a 100-cc. measuring-flask or into a measuring-cylin- 

 der, fill up to 100 cc., mix thoroughly, and again determine the amount 

 of rotation. It will be found to have increased (hydrolysis of the 

 milk-sugar into glucose and galactose, which latter rotates more to 

 the right than lactose). When glucose is treated in the same way 

 its rotation remains unchanged or decreases a little, in consequence 

 of the formation of humin substances. 



1 Or, instead of the mixture, 20 cc. of nitric acid, 1.3 specific gravity. 



