THE CARBOHYDRATES 



acid the following reactions take place. The first reaction reaulte in ,,1 



production of a hydrazone : 



CH 2 OH(CHOH) 3 CHOHCHO + H 2 N.NHC,H 

 CH 2 OH(CHOH) 3 CHOH.CH : N.NH.C 6 H 5 ' + H 2 0. 



The hydrazone then reacts with another molecule of phenyl hydrazine with 

 the production of an osazone : 



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

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



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 identifica- 

 tion of different carbohydrates. 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 recon- 

 verted 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 C0 2 , and f 

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



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

 are precipitated when the liquid is still hot, the precipitate being increased as 1 

 liquid cools. The crystals form bundles of fine yellow needles which are almo 

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

 they melt at 204-205 C. 



On treating a watery solution of glucose with benzoyl chloride and i-aus' 



