1914] Anton R. Rose and Katherine R. Coleman 4^9 



sometimes develops in Solutions of low NH4 content and by the fer- 

 ne hydrate-like precipitate formed when the ammonium salt is pres- 

 ent in two large amounts for nesslerizing, The chemist should 

 also be cautioned against a high reading due to the same source of 

 error, in which there is a partial exclusion of the light by colloidal 

 particles on the borderline between Suspension and true Solution. 

 In our experience, this adaptation or modification of the method 

 is very accurate for Solutions whose nitrogen content ranges from 

 0.0004 to 0.002 gm. per c.c. 



TABLE I 



Our practice has been to place the cup containing the cobalt- 

 platinum sol. at the 20 mm. point and to move the other cup so as 

 to get three readings moving down, and three in the upward direc- 

 tion. The Solution should be standardized to each arbitrary mark 

 selected for the readings. Though the readings are accurate 



