104 DEXTROSE. 



made for the monochromatic light corresponding to the D line of the 

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

 by (a) 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 = -i.?/Co> or ( a )o : ()j : : 21-65 : 24. Hence 



it is important in all cases to state clearly whether a given determi- 

 nation has been made for monochromatic yellow light or for the 'tran- 

 sition 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 de- 

 composed, the decomposition being accompanied by the precipita- 

 tion either of the metal (Hg) or of an oxide (Cu 2 0). 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 reduction effected by any given 

 sugar is, under given conditions, a constant quantity. 1 



Phenyl-glucosazone. C 18 H 22 N 4 O 4 . [C 6 H 10 O 4 (C 6 H 5 . N 2 H) S ]. 



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 laevo-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 



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

 tion 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 

 Koklenki/drate. 



2 Fischer, Ber. d. d. chem. Geseil. Bd. XXH. (1889), S. 90 (foot-note). 



