148 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



In the original arrangement the parts of the apparatus are suspended by wires from 

 clamps on a metal stand. The whole apparatus is thus moveable instead of being per- 

 manently fixed as in Fig. 34. 



By this means the bulb and pipette can be shaken mechanically so as to 

 hasten the reaction and facilitate the absorption of the nitric oxide evolved 

 by the action of acid upon the nitrite. For convenience, rubber tubing is 

 fastened to the tap of the bulb D, the burette B and the tap c, and arranged 

 so that the liquids can be passed straight into the sink. It is also con- 

 venient to have a small handle h on the driving wheel so as to shake the vessels 

 for short periods by hand. 



The manipulation is carried out in three stages : 



(1) Displacement of the air in the apparatus. 



The gas burette F is filled with water, the air being allowed to escape 

 through c, 



One bulb of the Hempel pipette is filled with a solution of alkaline per- 

 manganate. 1 By lowering the levelling bulb of the burette the air in the 

 Hempel pipette is drawn into the gas burette until permanganate just reaches 

 the tap. This air is driven out through c and water fills the gas burette 

 and connection as far as c. The tap c is turned so as to shut off this part 

 of the apparatus and to be in connection with D and the exit tube. 7 c.c. 

 of glacial acetic acid are put into A and run into D. About 30 c.c. of 

 sodium nitrite solution (30 per cent.) are put into A and run into D. 

 Sufficient nitrite solution should be used so that excess stands in A above the 

 tap. The tap c is closed by a quarter turn, and the bulb is shaken for a few 

 seconds. The nitric oxide which is evolved drives the liquid into A. By 

 opening the tap c to the exit, the liquid from A again fills the bulb D and 

 the gas passes out at c. The tap c is again closed and the shaking repeated. 

 The gas is let out and the shaking again repeated. In this way the air is 

 driven out of the bulb D. Finally, a space of about 20 c.c. should be left in the 

 bulb by shaking and driving the liquid into A ; the tap a is closed. 



Tap c is opened to connect D and F. 



(2) Decomposition of the amino substance. 



10 c.c. or less of the solution to be analysed is placed in the graduated 

 burette B ; any excess can be run off. The desired volume is run into D. 

 The burette B need not be graduated ; the desired amount can be introduced 

 with a pipette into B, run into D, and B washed with a little water, which is 

 also run into D. 



D is shaken for 3-5 minutes. Only in a few cases is longer shaking 

 necessary. If frothing occurs, as in the case of hydrolysed proteins, B can be 

 washed out and a little capryl alcohol introduced through B. 2 If the re- 

 action takes some time to complete, it is allowed to stand for the required 

 time and finally shaken for 2 minutes. 



The gas given off passes into the burette F. The residual gas in the bulb 

 is driven into the burette F by opening the tap a and filling D with solution 

 from A as far as the tap c. 



(3) Absorption of nitric oxide and measurement of the nitrogen. 



The tap of the burette F is turned so as to connect it with the Hempel 

 pipette. The gas is driven into the pipette by raising the levelling tube. The 

 Hempel pipette is shaken gently for 1-2 minutes, and the gas returned to 

 the burette and measured. It is driven over into the permanganate again and 

 returned to the burette. If no change in volume has occurred the volume is 



alcohol. 



1 50 gm. KMnO 4 + 25 gm. KOH per 1000 c.c. 



3 In later forms of apparatus another tube is sealed to D for introducing the capryl 



Ln! 



