FIXATION OF NITROGEN BY FUNGI 191 



Certain minor difficulties can be learned and mastered only 

 by experience and can not well be described in print. I learned 

 by experience that it was fairly easy to manage the difficulty 

 and annoyance caused by foaming. If the digestion is begun 

 with, acid and CUSO4 only, and continued with a low flame until 

 the foaming reaches the maximum, and the flame is then kept 

 extremely low, the critical point in the foaming may be passed 

 in less than one minute. Then the K2SO4 may be added a httle 

 at a time, when the foaming wdll diminish and nearly cease, 

 and the flame may then be turned up to its maximum. The 

 digestion will then go on to completion \\Hthout further difficulty. 



After the liquid becomes clear it is allowed to cool but not to 

 solidify. Then 6 to 10 cc. of water is added, or enough to keep 

 the hquid clear when the alkali is next added. A drop of indi- 

 cator is now added. Three cc. of saturated NaOH will be 

 sufficient to render the liquid alkaline. A good way to intro- 

 duce the alkali is to suck it up into the blowing tube and to hold 

 it there by means of a clamp until the rubber stopper is inserted 

 in the test-tube and made air tight, then the clamp may be re- 

 leased. The current of air may now be turned on, slowly at 

 first and increased towards the last to a maximum — as much as 

 the apparatus will stand. 



The ammonia is blown over into a 100 cc. volumetric flask 

 which contains 20 cc. of water and 2 cc. of w HCl. Wlien the 

 blowing is completed, which ^\'ill require about twenty minutes, 

 the volume may be made up to 50 cc. and the diluted Nessler's 

 reagent (5 cc. plus 20 of water) may be added with such care as 

 to -prevent any clouding. A standard flask made up in the 

 same manner and as nearly as possible at the same time, con- 

 taining a standard amount of nitrogen; in my case always 1 

 mgm. of the standardized (NH4)2S04 is used as the standard 

 of comparison for reading in the Duboscq colorimeter. It is 

 well to discard 20 to 30 cc. of each from the top and use from the 

 remainder. It is also well to wash the cups and glass prisms 

 of the colorimeter with the solution to be tested before proceeding. 



In my practice the standard was set at 20 on the colorimeter. 

 The ve.nier reading on the other side, taken in inverse ratio 

 gives the amount of nitrogen in milligrams. >^rCr \ C/T/ 



THE PLANT WORLD, VOL. 19, NO. 7, 1916 /L^J/© "rfVr 



[;<ai LIBRARY I- 



