142 
Journal of Agricultural Research 
Vol. IX, No. s 
methods of experimentation 
The soil samples employed in the investigations reported in this paper 
were secured by means of soil-sampling tubes or, where large quantities 
of soil were desired, by digging a hole to the desired depth and removing 
a uniform block of soil from the side. All the soils studied were passed 
through a coarse sieve, after which they were thoroughly mixed. 
One-hundred-gm. portions of dry soil were then weighed into i-quart 
Fig. x .—Diagram showing the percentage of ammonia recovered from soils when increasing amounts of 
ammonium sulphate were added. 
Mason jars. The desired amount of ammonium salts or other salts was 
added in standard solutions in such quantities that the solution added 
was sufficient to saturate the soil thoroughly. 
Unless otherwise stated in the text, the ammonium solution was 
allowed to remain in contact with the soil for 30 minutes. The soil 
was then extracted by a 10 per cent hydrochloric-acid solution and an 
aliquot portion of the extract, rendered alkaline by adding sodium- 
