36 PHYSIOLOGICAL CHEMISTRY. 



of 1.8 gram of Isevulose in 10 c.c. of water add 4 grams 1 of methyl- 

 phenylhydrazine and enough alcohol to clarify the solution. Intro- 

 duce 4 c.c. of 50 per cent acetic acid and heat the mixture for 5-10 

 minutes on a boiling water-bath. 2 On standing 15 minutes at room 

 temperature, crystallization begins and is complete in two hours. 

 By scratching the sides of the flask or by inoculation, the solution 

 quickly congeals to form a thick paste of reddish yellow silky 

 needles. These are the crystals of methylphenyllcEvulomzone. 

 They may be recrystallized from hot 95 per cent alcohol and melt at 



153 C. 



CH 2 OH 



GALACTOSE, (CHOH) 4 . 



CHO 



Galactose occurs with dextrose as one of the products of the 

 hydrolysis of lactose. It is dextro-rotatory, forms an osazone with 

 phenylhydrazine and ferments slowly with yeast. Upon oxida- 

 tion with nitric acid galactose yields mucic acid, thus differentiat- 

 ing this monosaccharide from dextrose and Isevulose. Lactose also 

 yields mucic acid under these conditions. The mucic acid test may 

 be used in urine examination to differentiate lactose and galactose 

 from other reducing sugars. 



EXPERIMENTS ON GALACTOSE. 



1. Tollens' Reaction. To equal volumes of galactose solu- 

 tion and hydrochloric acid (sp. gr. 1.09) add a little phloroglucin, 

 and heat the mixture on a boiling water-bath. Galactose, pentose 

 and glycuronic acid will be indicated by the appearance of a red 

 olor. Galactose may be differentiated from the two latter sub- 

 stances in that its solutions exhibit no absorption bands upon spec- 

 Iroscopical examinations. 



2. Mucic Acid Test. Treat 100 c.c. of the solution containing 

 galactose with 20 c.c. of concentrated nitric acid (sp. gr. 1.4) and 

 evaporate the mixture in a broad, shallow glass vessel on a boiling 

 water-bath until the volume of the mixture has been reduced to 

 about 20 c.c. At this point the fluid should be clear, and a fine 

 white precipitate of mucic acid should form. If the percentage of 

 galactose present is low it may be necessary to cool the solution 



1 3.66 grams if absolutely pure. 



" Longer heating is to be avoided. 



