76 THE CARBOHYDRATES 



in clusters resembling wheat sheaves. Glucosazone melts 

 at 204-205 with decomposition ; it is insoluble in water but 

 soluble in alcohol, the solution being laevo-rotatory in contra- 

 distinction to that of maltose which is dextro-rotatory. 



Microchemical Tests. 



For microchemical tests for sugars, the reduction of copper 

 salts in the presence of .excess of alkali is generally employed, 

 but these are not altogether satisfactory, owing to the amount 

 of diffusion which takes place, and also because sucrose, if its 

 presence in a tissue be suspected, must first be hydrolysed by 

 boiling with acid before the reduction will take place. 



Mangham * and others have obtained excellent results by 

 the use of the osazone test for microscopic work ; if properly 

 performed, it is much more satisfactory than any other, and 

 has the advantage of being a very delicate test for some sugars. 

 For example, a '015 per cent solution of glucose will give a 

 definite reaction. The main disadvantage of the method is in 

 its comparative slowness. 



Two solutions are required : 



(a) I gram of phenylhydrazine hydrochloride dissolved in 

 10 grams of glycerine. 



(8) I gram of sodium acetate dissolved in 10 grams of 

 glycerine. 



If necessary the solution of these substances may ' be 

 hastened by means of heat, and before use the solutions 

 should be filtered. 



Glycerine is used because its penetrative power is greater 

 than that of water, and also because it will not evaporate and 

 deposit crystals of the substances used. 



For use, one drop of each fluid is placed on a glass slip 

 and mixed thoroughly. The section, which must be more 

 than one cell in thickness, is laid in the mixture and covered 

 with a cover glass. The preparation is heated on a hot water 

 oven for about half an hour, and is then allowed to cool ; the 

 osazone crystals will form in varying degrees of rapidity. 



In order that familiarity with the method may be gained, 

 the reagents may be mixed on the slip with drops of sugar 



* Mangham: "New Phytol.," 1911, 10, 160; "Ann. Bot.," 1915, 29, 360. 



