1. A method is described for the estimation of small quantities of ammonia down to 0.001 µg. N.
2. The principle of the method is that ammonia is liberated from the sample and recovered in a solution of standard acid by Conway's diffusion method; the electrical conductance of the acid falls as ammonia is absorbed, due to the difference in the mobility of hydrogen and ammonium ions.
3. The results of estimations on standard ammonium sulphate solutions and biological fluids are tabulated. The method can deal with quantities down to 0.005 µg. ammonia-N with an error <± 2% (standard deviation), 0.001µg. ammonia-N with an error ± 6-8%.
4. An account is given of the construction of small diffusion chambers and small conductivity cells.