[Vol. 10 



332 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



adopted as the time of 



A laree number of deter 



minations were made with distilled H :0 and various solutions to 

 study the effect of duration of reaction on the quantity of Nt 

 evolved. A few determinations with 2 ml. of water are here 



given : 





Time in minutes 



ml. N, 



Temperature 23° C. 



3 



.08 





5 



.085 





5 



.09 





8 



.11 



Barometer 763 mm. 



20 



.12 





40 



.15 



The blank appears to vary regularly with the quantity of gas 



off by the 



Variations in the blanks are to be 



pected with different supplies and grades of nitrite and 



acid 



Potassium nitrite cannot be used because the reaction of 



this nitrite with glacial CH 3 COOH is too vigorous. Where 

 caprylic alcohol is used to overcome foaming a new blank must 

 be run. The speed of shaking should also be maintained as 

 nearly constant as possible. The time required to rid the re- 

 action vessel of air may be materially lessened by warming the 

 nitrite to 30° C. and shaking by hand during this preliminary 

 process. The motor, however, adjusted to a suitable and defi- 

 nitely maintained speed, should always be used for the reaction 

 shaking. To obtain reliable results the above precautions and 

 the following, as advised by Dr. D. W. Wilson, Department 

 Physiological Chemistry, Johns Hopkins Medical School, should 

 be carefully observed. The stopcocks, especially the one just 

 above the gas burette, should be kept well greased with the 

 vaseline-paraffin-rubber preparation recommended by van Slyke; 

 this should be done after every 3 or 4 determinations. After 

 200-300 determinations the stopcocks should be ground gently 

 with powdered emery and oil followed by talcum in water. The 

 method is not very satisfactory for solutions containing peptones 

 or proteins; accordingly the results given for "peptid" N of the 

 two peptone media are to be more dependable than those for 



"total amino." 



In the procedure for determining " peptid" N a 50-ml. portion 

 of the medium was hydrolyzed 3 to 5 hours with 20 per cent HC1, 



