The experiments described in the following pages were made with a view to discover how far purely physical and chemical processes, known to take place in the soil, may be expected to give rise to nitrites and nitrates. Scattered throughout the extensive literature on nitrification are occasional papers tending to show, what might also be expected on theoretical grounds, that non-bacterial processes may be important sources of nitrates. Formerly these processes were considered to be the only sources, then came the brilliant researches of Schloesing and Muntz, Warington, Winogradsky, and others on nitrifying organisms, and non-bacterial processes were forced into the background. Now that a full knowledge of the various sources of nitrogen compounds in the soil has become so indispensable to the agriculturist, it seemed desirable to make a careful examination of the various chemical and physical processes known to take place in the soil, and to ascertain whether they make any direct or indirect contribution to its stores of nitrates. To this end we have repeated and extended such of the recorded observations bearing on the subject as seemed to merit repetition; we have also devised other experiments to make the examination as complete as possible.