THE CARBOHYDRATES 63 



CH 2 (OH)(CHOH) 3 CHOH.CH : N.NH.C 6 H 5 + H 2 N.NHC 6 H 5 *= 

 CH 2 OH(CHOH) 3 C.CHN.NH.C 6 H 5 



II 

 N.NH.C 6 H 5 + H 2 + H 2 . 



The hydrogen formed in this reaction acts upon a second molecule of phenyl hydrazine, 

 splitting it into aniline and ammonia. On this account it is always necessary to have 

 an excess of phenyl hydrazine in the operation. 



The osazones form well-defined crystalline products which are generally yellowish 

 in colour and differ in their melting-point and in their crystalline form. They are 

 therefore of extreme value in the separation and identification of different carbohy- 

 drates. They can be also used for the artificial preparation of certain sugars. Under 

 the influence of acetic acid and zinc dust they form osamines, which on treatment with 

 nitrous acid are reconverted into the corresponding sugar, generally a ketose. 



GLUCOSE, DEXTROSE or GRAPE SUGAR, is the chief constituent of the 

 sugar of fruits, especially of grapes. It occurs in the body as the end- 

 product of the digestion of starch. When pure it forms white crystals which 

 melt at 100 C., and lose the one molecule of water of crystallisation at 

 110 C. It is easily soluble in water, and the solution shows bi-rotation. 

 Its final specific rotatory power at 20 C. is 52 *74. 



TESTS FOR GLUCOSE. Trommer's test depends on the power possessed in 

 common with the other sugars of reducing cupric hydrate to cuprous oxide. The 

 sugar solution is made alkaline with caustic potash or soda, and a few drops of copper 

 sulphate solution added. On heating the blue solution thus obtained to boiling, it 

 turns yellow, and a yellowish-red precipitate of cuprous hydrate is produced. This 

 test is generally performed with Fehling's solution, which consists of an alkaline solution 

 of cupric hydrate in Rochelle salt. The proportions in making the solutions are so 

 arranged that 10 c.c. of Fehling's solution are completely reduced by -05 gramme glucose. 

 This reaction is made use of for the quantitative determination of glucose in solution. 

 The determination may be carried out either volumetrically, as in Fehling*s or Pavy's 

 method, or gravimetrically, as in Allihn's method. 



Moore's Test. A solution of glucose treated with a little strong caustic potash 

 or soda and warmed, becomes first yellow and then gradually dark brown, and gives 

 off a smell of caramel. 



With ordinary yeast, glucose solutions ferment readily, giving off CO 2 , and form 

 alcohol with small traces of amyl alcohol, glycerin, and succinic acid. 



With phenyl hydrazine glucose gives well-marked needles of glucosazone. These 

 are precipitated when the liquid is still hot, the precipitate being increased as the 

 liquid cools. The crystals form bundles of fine yellow needles which are almost in- 

 soluble in water, but are soluble in boiling alcohol. When purified by recrystallisation 

 they melt at 204-205 C. 



On treating a watery solution of glucose with benzoyl chloride and caustic soda 

 and shaking till the smell of benzoyl chloride has disappeared, an insoluble precipitate 

 is produced of the benzoic ester of glucose. This method has been often used for 

 isolating glucose from fluids in which it occurs in minute quantities. 



Molisch's Test. On treating 0-5 c.c. of dilute glucose solution with one drop of a 

 10 per cent, alcoholic solution of a-naphthol, and then pouring 1 c.c. of concentrated 

 sulphuric acid gradually down the side of the tube, a purple ring is produced at the 

 junction of the two fluids, which on shaking spreads over the whole fluid. This reaction 

 depends on the formation of furfurol from the glucose. 



tin order to identify glucose in a normal fluid, the following tests may be applied, 

 3r removing any protein which may be present : 

 (1) Reduction of cupric hydrate or Fehling's solution. 





