1218 



DEXTROSE. 



sels and observations on their subsequent appearance in the 

 urine. 



When pure, dextrose is colourless and crystallizes from its 

 aqueous solution in six-sided tables or prisms, often agglomer- 

 ated into warty lumps. The crystals will dissolve in their own 

 weight of cold water, requiring however some time for the 

 process ; they are very readily soluble in hot water. Dextrose 

 is somewhat sparingly soluble in cold ethyl-alcohol, more soluble 

 in warm; slowly soluble, but in considerable quantity, in methyl- 

 alcohol and insoluble in ether. 



A freshly prepared cold aqueous solution of dextrose pos- 

 sesses a specific rotatory power for monochromatic yellow light 

 of (a) D = + 100. This rapidly falls, especially on warming, 

 until it may be taken as (a) D = 4-52-5 for solutions which do 

 not contain more than 10 p.c. of the sugar. The rotation is 

 however dependent on the concentration of the solution being 

 least with very dilute solutions. 



Dextrose readily forms compounds with alkalis and salts, 

 which 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 accom- 

 panied by the precipitation either of the metal (Hg) or of an 

 oxide (Cu 2 O). This fact provides the basis for the more impor- 

 tant 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 condi- 

 tions, a constant quantity. 



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



This compound of dextrose with phenyl-hydrazine crys- 

 tallizes in yellow needles. It is almost insoluble in water, very 

 slightly soluble in hot alcohol, melts at about 205 and is Irevo- 

 rotatory when dissolved in glacial acetic acid. 



An important property of dextrose is its power of undergo- 

 ing fermentations. Of these the principal are : (1) Alcoholic. 

 This is produced in aqueous solutions of dextrose, under the 

 influence of yeast. The decomposition is the following : 

 C 6 H 12 O 6 = 2C 2 H 6 O + 2CO 2 , yielding (ethyl) alcohol and carbon 

 dioxide. Higher alcohols of the fatty series are found in 

 traces, as also are glycerin, succinic acid and probably many 

 other bodies. The fermentation is most active at about 25 C. 

 Below 5 C. or above 45 C. it almost entirely ceases. If the 

 saccharine solution contains more than 15 per cent, of sugar it 

 will not all be decomposed, as excess of alcohol stops the reac- 



