A method for the determination of ammoniacal nitrogen in soils is described. It is an extension of the Hissink method for exchangeable bases to ammonium present in the soil. The working details are similar to the Hissink method, except that the leaching process is entirely carried out in the cold. The ammonia is distilled off with magnesium oxide.

Using normal sodium chloride as a leaching solution and collecting half a litre of leachings for distillation with magnesia, results were obtained which showed excellent agreement with those by the aeration method. Similar results were obtained using 250 c.c. of 15 per cent, sodium chloride solution, but the results are on an average about 1·6 per cent, lower. With high proportions of ammoniacal nitrogen a second half litre of normal sodium chloride leachings should be taken, or half a litre of 15 per cent, solution used.

The leaching method is economical of apparatus and water supply. It is therefore suitable for small laboratories with limited resources. It is fairly rapid: six estimations can be completed in a day.

The close agreement of the new method with the aeration method suggests that the amount of ammoniacal nitrogen in the soil at any given time is not an arbitrary quantity depending on conditions of estimation, but a definite amount. It is improbable that any ammonium compounds exist in the soil apart from those which take part in base exchange.