SOIL FERTILITY AND PHOSPHORIC ACID. 
G. S. Fraps, Ph. D.* 
The development of agricultural chemistry is intimately connected 
with the theories concerning the nature of soil fertility. In the begin- 
ning or the rudimentary stages of agricultural chemistry, it was be- 
lieved that plants, like animals, lived upon organic matter. To feed 
plants and to maintain soil fertility, the soil must be filled with organic 
matter — manure. The mineral matter contained in plants — the ash — 
was not essential, but acted as a stimulant. Such was the humus theory, 
as it was called, a theory which, like all theories generally held, con- 
tained something of truth, though in itself erroneous. The application 
of sufficient manure to the soil goes far towards maintaining soil fer- 
tility, though not for the reason contained in the theory. 
The great German chemist, Justus von Liebig, directed his attention 
to chemistry in its application to agriculture, and in 1843, published 
a book in which the humus theory was demolished on theoretical 
grounds. In its place was set up the mineral theory, according to 
which the mineral matters taken from the soil were the essential con- 
stituents for fertility. The experimental proofs for this theory were 
not long in being produced. Liebig himself, as an object lesson, trans- 
formed a barren, sandy piece of land near Giessen, Germany, into a 
beautiful garden, entirely by means of mineral manures. Plants were 
grown in water solutions of mineral salts without any organic matter 
whatever, and they grew vigorously and produced seed. By leaving out 
one or the other elements from the water solution and observing the 
growth of the plant, it was soon established which elements were essen- 
tial to the growth of the plants and which were only useful, or of no 
use at all. 
Modern agricultural chemistry may be said to begin with this book 
of Justus von Liebig. We may trace directly from it the field experi- 
ments of the young John Lawes at his manor place of Eothamsted, 
England — his discovery of the effect of treatment with sulphuric acid 
upon the manural effects of mineral phosphates, his patent on the pro- 
cess, and, incidentally, the fortune he made from it. We find the 
experiments continued, with the aid of Henry Gilbert; honors were 
heaped upon them — they are now Sir John Lawes and Sir Henry Gil- 
bert; Eothamsted is the most famous experimental place in the world, 
■^Chemist, Texas Experiment Station, College Station, 'Texas. 
