...concentrated and 75 cc of fuming sulphuric acid 13 per cent SO3 and heating at 100° C. for 2 hours), rubbing with a glass rod to insure intimate contact....manner with phenol disulphonic acid reagent. Compare iu the usual manner and record as nitrogen in the form of nitrates. (Note: A portion of the standard...

...concentrated and 75 cc of fuming sulphuric acid 13 per cent SOS and heating at 100° C. for 2 hours), rubbing with a glass rod to insure intimate contact....until the maximum color is developed. Transfer to a colori metric cylinder, filtering if necessary, and compare with a standard potassium nitrate solution...