In 1927 GILBERT and HARDIN (4), and later GILBERT and SMITH (5), published data showing that there is a correlation between soil fertility and the chemical composition of expressed plant juice. MCCooL and WELDON (7) and PETTINGER (8) in more recent work have substantiated the findings of GILBERT et al. The juice work of the Rhode Island workers has recently been extended to include the estimation of a number of the nitrogenous fractions. This has necessitated a study of methods, since the present chemical procedures used in plant work have been developed for water or alcoholic extracts of plant tissue. Accordingly the method for the determination of ammonia was chosen for adaptation to expressed juices, for the estimation of this plant constituent is one of the most frequent determinations made in the study of plants at this station.