In 1840 (ever-memorable year), while at Giessen, Liebig published his famous and epoch-making work on agricultural chemistry, Die organische Chemie in ihrer Anwendung auf Agricultur und Physiologie. Although Davy, thirty years before, had published a work on Agricultural Chemistry, it was not until Liebig's book made its appearance that any great stride was made in the scientific principles of agriculture. This book is one of those few works which stand out from all others on the subjects of which they treat. It is undoubtedly the most important work on agriculture ever given to the world as the result of one man's researches and ideas. From the land of Kant, Fichte, Schelling, Schiller, and other philosophers, it is not surprising that we have such a far-reaching and philosophic work as Liebig's Die organische Chemie given to us.
That an increase of solubility in bones and other phosphates would be attended by an increased productive power in the crop, was the idea of Liebig. He, in 1840, recommended, in lieu of bones, the use of the substance long well known to chemists as the acid or superphosphate of lime, which is producible from bones and other phosphates by the action of oil of vitriol or sulphuric acid. Practice has since shown the great advantage of Liebig's suggestion.
The chief point of Liebig's famous book was to show that the humus of the soil is powerless to build up com-
