104 DEXTROSE. 



determination being made for the monochromatic light corresponding to the D line 

 of the solar spectrum. In this case the specific rotatory power is represented by 

 (O.)D. In another class the mean yellow light of an argand or paraffin lamp is 

 employed. In this form of polarimeter the field of the instrument when adjusted 

 for use is of a pale pinkish-violet colour, called from the extreme sensitiveness with 

 which it changes from pink to violet or the reverse the ' transition tint ' (teinte de 

 passage). This colour is complementary to yellow (jaune), and specific rotatory 

 powers determined for this particular colour are represented by (a)j. For any given 



substance (a) D is always less than (a)j, and for ordinary purposes ( a )D=^?fe or 



(a) D : (a)j :: 21-65 : 24. Hence it is important in all cases to state clearly whether 

 a given determination has been made for monochromatic yellow light or for the 

 ' transition tint ' of mean yellow light. 



Dextrose, like all alcohols, readily forms compounds with acids 

 and many salts, of these the latter are the more important and are in 

 many cases characteristic, as for instance those with caustic alkalis 

 and sodium chloride. When heated many of these compounds, more 

 particularly those of bismuth, copper and mercury, are decomposed, 

 the decomposition being accompanied by the precipitation either of 

 the metal (Hg) or of an oxide (Cu 2 O). This fact provides the basis for 

 the more important methods of detecting the presence of dextrose and 

 other sugars with similar reducing powers, and of estimating them 

 quantitatively in solution, since it is found that the amount of reduc- 

 tion effected by any given sugar is, under given conditions, a constant 

 quantity 1 . 



Phenyl-glucosazone. C^H^NA. [C 6 H 10 O 4 (C 6 H 5 . N 2 H)J. 



This compound of dextrose with phenyl-hydrazin crystallises in 

 yellow needles. It is almost insoluble in water, very slightly soluble 

 in hot alcohol, melts at about 205 and is lee vo- rotatory when dissolved 

 in glacial acetic acid. The phenyl-hydrazin test for dextrose is applied 

 as follows. To 50 c.c. of the suspected fluid (e.g. diabetic urine) add 

 1 2 grm. hydrochloride of phenyl-hydrazin, 2 grm. sodium acetate, and 

 heat on a water-bath for half an hour; or else add 10 20 drops of pure 

 phenyl-hydrazin and an equal number of drops of 50 p.c. acetic acid and 

 warm as before 2 . On cooling, if not before, the glucosazone separates 

 out as a crystalline or it may be amorphous precipitate. If amorphous 

 it is dissolved in hot alcohol, the solution is then diluted with water and 

 boiled to expel the alcohol, whereupon the compound is obtained in 

 the characteristic form of yellow needles. By the above method it is 



1 The description of the various methods employed for the detection and 

 estimation of dextrose and other sugars lies outside the scope of this work. Full 

 details are given in Neubauer u. Vogel, Analyse des Hams, and Tollens' Handbuch der 

 Kohlenhydrate. 



2 Fischer, Ber. d. d. chem. Gesell. Bd. xxn. (1889), S. 90 (Foot note). 



