The fact which Liebig had denounced and which prompted Schönbein’s investigations, was this :
The upper layers of the soil always contain more ammonia than the deeper ones, instead of containing less of it as they would have to do if they had lost it through cultivation. The fact was recognised by every chemist. Only the cause was unknown.
Hitherto, decay was considered to be the sole source of ammonia. All chemists (including Liebig) denied that the nitrogen in the air could serve as a nutrient for plants.
Schönbein proved (by experiment) that any flame burning in the air converts a certain quantity of the nitrogen in the air into ammonium nitrate, that every process of decomposition gives rise to both nitric acid and ammonia, that the mere evaporation of water is the means causing the formation of both plant nutrients.
Finally, Liebig’s “jubilation” at this discovery :
The combustion of a pound of coal or wood restores to the air not merely the elements needed to reproduce this pound of wood or, under certain conditions, coal, but the process of combustion in itself (note the Hegelian category [Marx’s insertion]) transforms a certain quantity of nitrogen in the air into a nutrient indispensable for the production of bread and meat.
I feel proud of the Germans. It is our duty to emancipate this “deep” people.