ying the importance of supplying
nitrogen as a manure; and secondly, in overestimating the amount of
ammonia washed down in rain, which has subsequently been shown to be
entirely inadequate to supply plants with the whole of their
nitrogen.[15]

_His Theory of Rotation of Crops._

In explaining the benefits of the rotation of crops, Liebig propounded a
very ingenious theory, but one which was largely of a speculative
nature, and which has since been shown to be unfounded on any scientific
basis. It was to the effect that one kind of crop excreted matters which
were especially favourable to another kind of crop. He did not say
whether he considered such excretion positively injurious to the crop
which excreted them; but he inferred that what was excreted by the crop
was what was not required, and what could, therefore, be of little
benefit to a crop of the same nature following it.

The second portion of Liebig's report dealt with the processes of
fermentation, decay, and putrefaction.

_Publication of Liebig's Second Report to British Association._

In 1842 Liebig contributed his second famous report to the British
Association, subsequently published under the title of 'Animal
Chemistry; or, Organic Chemistry in its Applications to Physiology and
Pathology.' The publication of this report created even greater interest
than the publication of his first work. In it he may be said to have
contributed as much to animal physiology, as, in his first, he did to
agricultural chemistry. His subsequent principal works on agricultural
chemistry were--'Principles of Agricultural Chemistry,' published in
1855, and 'On Theory and Practice in Agriculture,' 1856.

_Liebig's services to Agricultural Chemistry._

An attempt has been made to sketch in the very briefest manner some of
the main points in Liebig's teaching, as contained in his famous report
to the British Association in 1840. Agricultural chemistry up till that
year can scarcely be described as having a distinct existence as a
branch of chemistry. Much valuable work, it is true, had already been
done, especially by his two great predecessors, de Saussure and
Boussingault; but it was, down to the year 1840, a science made up of
isolated facts. Liebig's genius formed it into an important branch of
chemistry, supplied the necessary connection between the facts, and by a
series of brilliant generalisations formed the principles upon which all
subsequent advance has