ANAEROBIC RESPIRATION 69 



The gas is passed through two wash bottles of concentrated 

 alkaline solution of pyrogallol in order to remove the small 

 amounts of the admixture of oxygen and carbon dioxide. The 

 presence of the noble gases is of course unimportant. If no 

 compressed nitrogen is available, this gas may be prepared as 

 follows. In a round-bottomed flask are mixed i part of sodium 

 nitrite, 2 parts of ammonium sulphate, i part of K-^CrOt, and 

 about 7 cc. of water. The flask is closed with a rubber stopper 

 and an exit tube, and cautiously heated with a small flame. 

 The reaction proceeds according to the equation: 



(I) (NH4)2S04 + 2NaN03 = NaoS04 + 2NH4NO.2 



(II) NH4NO2 = N2 + 2H2O. 



The following reaction also takes place in traces : 

 3HNO2 = HNO3 + 2NO + H2O. 



The escaping gas passes through a vessel containing soda 

 lime or pieces of KOH the size of peas, then either through a 

 wash bottle filled with chromic acid mixture (5 vol. of a satu- 

 rated potassium bichromate solution to i vol. of cone, sulphuric 

 acid) or through a short combustion tube with a spiral of reduced 

 copper (10-15 cm. long), such as is used in analyses for the 

 elements. The copper spiral is kept red-hot by heating with a 

 suitable burner. ■ This purification of the gas is for the purpose 

 of destroying the nitric oxide. 



This method of preparation of nitrogen is rather simple, and 

 the gas is obtained in a pure state. It is also possible, by suit- 

 able warming or coohng of the flask, to regulate the velocity of 

 the current of gas. For an easier regulation the exit tube is 

 fitted with a side tube which dips into mercury and functions 

 as a safety valve. With the help of this valve and a glass stop- 

 cock or screw pinchcock it is possible to govern perfectly the 

 velocity of the current of gas. Still, the apparatus requires 

 constant oversight and so is not commendable for a continuous 

 experiment with a current of gas. It is best to drive the air 

 out of the plant containers with nitrogen, to seal the containers 

 air-tight, and then to work by the use of gasometric methods. 

 If the Kostychev flasks (Fig. 8) are used the procedure is as 



