92 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



There is above D a small bulb which .keeps the reacting solution 

 from splashing into the capillary. 



The deaminising bulb D is connected through a three-way tap c 

 with the gas burette F, which is of 150 c.c. capacity ; its upper and 

 narrower portion holding 40 c.c. is graduated in tenths ; its lower and 

 wider portion in 10 c.c. divisions. This large burette will hold all 

 the gas which is liberated whilst the apparatus is being used. The 

 gas, which is to be finally measured, should only fill a portion of the 

 narrow accurately graduated part. It is filled with water. The gas 

 burette is connected with the Hempel pipette of special shape, 

 which contains an alkaline solution of potassium permanganate. 

 Though the nitric oxide reduces the permanganate, the manganese 

 dioxide formed is in such a fine state of division that it does not in- 

 terfere with the manipulation. Several determinations can be made 

 with the same solution. Deposition of manganese dioxide in the 

 capillary tube is prevented by allowing water from the gas burette, in- 

 stead of permanganate, to remain in this tube. Any carbon dioxide 

 evolved is absorbed by the alkali. 



The glass connecting tubes are strong walled and of 3 mm. 

 internal diameter ; the bore of tap a is also of 3 mm. and tap d should 

 have the same wide bore. The connection between D and B should 

 be at least 8 mm. inner diameter, so as to allow free circulation. 



The nitric oxide is obtained from an excess of sodium nitrite solu- 

 tion which is decomposed by glacial acetic acid ; less nitric oxide is 

 evolved by its use than by the use of mineral acid. The amino sub- 

 stance may be dissolved in semi-normal acid, 50 pejp cent, acetic acid, 

 or normal alkali. 



Only a small correction for the reagents is necessary ; commercial 

 nitrite gave 0*2 c.c. of nitrogen for five minutes' reaction, 0*3 c.c. for 

 thirty minutes, and 0-5 c.c. for two hours. 



The estimation is performed in the following way : 



(i) Displacement of the Air in the Apparatus. The gas burette 

 F is filled with water as far as the tap r, the' air being allowed to 

 escape through c. One bulb of the Hempel pipette is filled with 

 alkaline permanganate solution 1 through a small funnel, the tap / 

 being arranged so that the air is displaced into the burette. The 

 permanganate should just reach the tap, which is then closed in 

 this direction and opened towards the tap c. The air in the burette is 

 driven out through c so that water again fills the burette as far as 

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



