CHEMICAL COMPOSITION OF PROTEIN MOLECULE 73 



All the glass tubing is of medium bore capillary tubing. 



The manipulation is as follows : 



Draw the liquid from the absorption pipette through the three-way 

 stop-cock A, which is then turned so that it connects with the burette 

 B and with the air at C. 



Pour 28 c.c. nitrate solution into reservoir D; draw it into E by 

 lowering the levelling bulb of the burette B, leaving a little liquid above 

 the cock F. 



Discharge the air in the burette B through A ; it is not necessary 

 to fill the capillary tube with liquid. 



Pour the solution to be analysed into G. 



Then pour 7 c.c. of glacial acetic acid into D and allow it to flow 

 into E by lowering the levelling bulb of the burette. Some acid must 

 remain above the stop-cock F. 



The gas evolved displaces the air in E. When 45-50 c.c. of 

 gas have been collected in the burette, close H and open F. A 

 gas space of sufficient size soon forms in E. 



Meanwhile drive the gas out of the burette through A, filling the 

 capillary with liquid and allowing the excess to run into the test 

 tube C. 



Close H and turn A so as to connect the absorption pipette with B. 



Close F and draw liquid from G into E, being careful not to run it 

 below J. 



Close J ; wash G with a little water and run it into E. Repeat 

 two or three times. 



When the reaction has proceeded for five minutes, draw the liquid 

 from D into E until it reaches H. 



Force the gas from the burette into the absorption pipette so that 

 the acid solution fills the capillary of the pipette. The time of absorp- 

 tion of the nitric oxide is reduced, if the pipette be shaken whilst the 

 gas is passed into it. 



The unabsorbed gas is returned to the burette, the permanganate 

 being drawn as far as H. 



The gas is then measured ; further treatment with permanganate and 

 further time for the reaction may be given by repetition of the processes. 



The apparatus is cleaned by forcing out the liquid through K. 

 Distilled water is admitted through D and G into E and the vessels 

 washed two or three times. It is convenient to support the apparatus 

 on a grooved cork at L. 



Amyl alcohol, if necessary, is added through D before the admis- 

 sion of the nitrite solution, or through G. 



