v] HYDROLYZING ENZYMES 49 



(6) Trom^ier's test. Add a few drops of a 1 / copper sulphate solution to 2-3 c.c. 

 of 5 % caustic soda solution. A blue precipitate of cupric hydroxide is formed. Add 

 now 2-3 c.c. of the glucose solution, and the precipitate will dissolve. On boiling, 

 the blue colour disappears, and a yellow or red precipitate of cuprous oxide is formed. 

 If only a little sugar is present the blue colour will disappear, but no oxide may 

 be formed. 



(c) Fehling's test. Boil a few c.c. of freshly made Fehling's solution in a test-tube 

 and note that it is unaltered. Then add an equal quantity of the glucose solution 

 and boil again. A red precipitate of cuprous oxide is formed. 



(cT) Osazone test. Take 10 c.c. of a 0'5 / solution of glucose in a test-tube and 

 add as much solid phenylhydrazine hydrochloride as will lie on a sixpenny piece, 

 at least twice as much solid sodium acetate and also 1 c.c. of strong acetic acid. 

 Warm gently until the mixture is dissolved and filter into another test-tube. Then 

 place the tube in a beaker of boiling water for at least ^ hour, keeping the water 

 boiling all the time. Let the test-tube cool slowly, and a yellow crystalline deposit 

 of phenylglucosazone will separate out. Examine this under the microscope and it 

 will be found to consist of fine yellow needles variously aggregated into sheaves and 

 rosettes. Glucosazone melts at 204-205 C. 



The osazone reaction takes place as follows : 



CH 2 OH(CHOH) 4 CHO + H 2 N-NHC 6 H. 5 = CH 2 OH (CHOH) 4 CH : N -NHC 6 H 5 + H 2 O. 



Glucose phenylhydrazone 



The phenylhydrazone is very soluble, but if an excess of phenyl- 

 hydrazine is used, a second hydrazine complex is introduced and an 

 insoluble osazone is formed : 



CH 2 OH (CHOH) 3 C CH : N NHC G H 5 



II 

 N-NHC 6 H 6 



Glucose reacts in this way by virtue of its aldehyde group. Phenyl- 

 hydrazine hydrochloride does not give an osazone when boiled with 

 glucose unless excess of sodium acetate be added. This acts on the 

 hydrochloride to form phenylhydrazine acetate and sodium chloride. 



Galactose. Galactose rarely, if ever, occurs free in plants, though it 

 is fairly widely distributed in the form of condensation products, the 

 galactans, in combination with other hexoses and with pentoses (see p. 60). 

 These galactans form constituents of various gums, mucilages, etc. 

 Agar-agar, which is a mucilage obtained from certain genera of the Red 

 Seaweeds (Rhodophyceae), yields a high percentage of galactose on 

 hydrolysis with acids. Galactose also occurs as a constituent of some 

 glucosides from which it may be derived on hydrolysis. 



One of the most important reactions of galactose is the formation of 

 mucic acid on oxidation with nitric acid. Mucic acid is practically 

 insoluble in water and separates out as a crystalline precipitate on 

 pouring the products of oxidation into excess of water. 



o. A. 



