178 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



5. Barfoed's Reagent. Dissolve 1 part of cupric acetate in 15 parts of 

 water ; to 200 c.c. of this solution add 5 c.c. of acetic acid containing 38 per 

 cent, of glacial acetic acid. Dextrose reduces this reagent on boiling ; 

 maltose and lactose do not. This test is not very delicate, and the reagent 

 must be freshly prepared. 



6. The Polarimeter. Estimate the strength of a solution of dextrose by 

 means of the polarimeter (see Appendix). 



7. Formation of Mucic Acid. Take 1 gramme of lactose and heat it in a 

 porcelain capsule with 12 c.c. of nitric acid on a water-bath until the fluid is 

 reduced to one-third of its original volume. A precipitate of imicic acid 

 separates out. Cane sugar, maltose, dextrose, dextrin, and starch treated in 

 the same way, yield an isomeric acid called saccharic acid, which, being 

 soluble, does not separate out. Lactose yields both acids ; galactose muck- 

 acid only. 



8. Fentoses give the ordinary reduction tests for sugar and yield osazones, 

 but do not ferment with yeast. They give the two following characteristic 

 tests ; they may be performed with gum arable (which contains arabinose) 

 or pine-wood shavings (which contain xylose). 



(a) Phloroglucin reaction. Warm some distilled water with an equal 

 volume of concentrated hydrochloric acid in a test-tube and add phloroglucin 

 until a little remains undissolved. Add a small quantity of gum arabic, 

 and keep the mixture warm in the water-bath at 100 C. The solution 

 becomes cherry-red, and a precipitate settles out, which is soluble in amyl 

 alcohol. This solution gives an absorption band between the D and E lines. 



(b) Orcin reaction. Substitute orcin for phloroglucin in the foregoing 

 experiment. The solution becomes violet on warming, then blue, red, and 

 finally green. A bluish green precipitate settles out, soluble in amyl alcohol. 

 This solution gives an absorption band between C and D. 



9. Glycuronic acid gives all the above reactions ; it may be distinguished 

 as follows : 



Take 50 c.c. of glycuronic acid solution in a capsule ; add 1 gramme of 

 p-bromphenyl-hydrazine and rather more than the same amount of sodium 

 acetate. Keep the mixture in the water-bath at 100 C. for a quarter of an 

 hour, when yellow crystals of ^p-bromphenyl-hydrazone separate out. After 

 cooling filter off the crystals and wash them with absolute alcohol, in which 

 they are insoluble. Under the same conditions carbohydrates yield p-brom- 

 phenyl-osazones, but these j},re soluble in absolute alcohol. The _p-brom- 

 phenyl-hydrazone is soluble in absolute alcohol to which pyridine has been 

 added ; the rotatory power of this solution is greater than that of any of the 

 osazones. 



