20 PRACTICAL PHYSIOLOGY. [ill. 



(/.) The solution is precipitated by alcohol (2 parts absolute 

 alcohol to I part of the solution). 



{g. ) Heated witli potash or acetic acid the opalescence diminishes, and the 

 solution becomes clear. 



{h.) Its solutions (even .6 per cent.) are powerfully dextro-rotatory 

 (a)D = 2ii° {Kiilz). 



8. V. Glucose, Dextrose, or Grape-Sugar {O^^fi^. — In com- 

 merce it occurs in warty uncrystallised masses of a yellowish or 

 yellowish-brown colour. It exists in fruits, and in small quantities 

 in the blood and other fluids and organs. It is the form of sugar 

 found in diabetic urine. It is readily soluble in water. Prepare a 

 solution by dissolving a small quantity in water. 



(a.) Taste the glucose, and note 

 that it is not so sweet as cane- 

 sugar. 



{h.) Add iodine solution = no 

 reaction. 



{c.) Heat the solution with sul- 

 phuric acid = darkens slowly. 



{d.) Dissolve some in boihng 

 absolute alcohol. It crystalUses in 

 transparent prisms when the alco- 

 rm.5.-Dextrose. hol COols (fig 5). 



As to the tests, they have been classified as follows : — 

 (A.) YeUow Colouration with Caustic Soda or Potash. 



(e. ) Moore's Test. — Heat the solution with half its volume of caustic soda = 

 a yellow or brown colour due to the formation of glucic and melassic acids. 

 The non-a])j)earance of a yellow colour indicates the absence of dextrose, but 

 tlie following substances also give a yellow colour with NaHO : — All the 

 glucoses, together with milk-sugar and lactose. 



(B.) Tests Depending on Reduction. 



(/:) Trommer's Test. — To the solution add a few drops of a 

 dilute solution of copper sulphate (lo per cent.), and afterwards 

 add caustic soda (or potash) in excess, i e., until the precipitate first 

 formed is re-dissolved, and a clear blue fluid is obtained. The 

 hydrated oxide of copper precipitated from the copper sulphate is 

 held in solution in presence of dextrose (and of all the glucoses). 

 Heat slowly, turning the tube in the flame. A httle below the 

 boihng point, if grape-sugar be present the blue colour disappears, 

 and a yellow (cuprous hydrate) or red (cuprous oxide) precipitate is 

 obtained. Boil the upper surface of the fluid, and when the yellow 

 precipitate occurs it contrasts sharply with the deep blue-coloured 

 stratum below. The precipitate is first yellow, then yellowish-red. 



