58 University of California Publications in Agricultural Sciences [Vol. 1 



often from one to one and one-half milligrams of nitrogen, or 

 about the amounts which appear to be lost where large quantities 

 of nitrates are determined by this method. 



As a means of comparison, the same amounts of "alkali" 

 salts and nitrate were added and the entire series analyzed by 

 the phenoldisulphonic acid method. The results of this work are 

 shown in the last column of Table II. The standard method 

 here calls for the use of 2 c.c. of the phenoldisulphonic acid, but 

 we found that even where no foreign salts were present, if the 

 amount of nitrate nitrogen exceeded about 10 mgs. 4 c.c. were 

 necessary to complete the reaction. 



The results of tests of the colorimetric method where large 

 amounts of nitrates were present, using respectivelj^ 2 and 4 c.c. 

 of the phenoldisulphonic acid, follow: 



To ascertain whether or not 4 c.c. portions of the acid were 

 sufficient. 6 c.c. quantities were tried. No gains in the amount 

 of nitrate nitrogen recovered here resulted. Four c.c. portions 

 were employed in the experiments reported in Table II. 



It is interesting to note that while my results confirm the 

 w^ork of Lipman and Sharp on the effects of Nad and Na^SO^ 

 on the phenoldisulphonic acid method, they are partly at variance 

 with them on the effects of NaXO,.... The investigators named 

 found that the nitrate determination liy the method mentioned 

 M-as in no wise affected by Na.CO..,. but it should be recalled that 

 they employed comparatively small quantities of nitrates and 

 carbonates and that in the presence of larger quantities the 

 chances of error are magnified. 



