238 S. W. Johnson on the Soil-analyses of the 
of the Kentucky soils, we may assume, that taken to the depth 
of a foot, an acre of soil weighs 3,000,000 Ibs. All that is re- 
moved by the heaviest wheat crop then in one year is but 35,307) 
or 0-0083-+ per cent. 
It follows that the annual removal of the heaviest crop of 
might appear extraordinarily fertile. Boussingault found in his 
Ti oil in June, during wet weather, 000034 per cent 
and reported by the distinguished Magnus. The account of 
ese experiments is given in detail in Erdmann’s Journal fur 
Praktische Chemie, vol. xlviii, pp. 447 et seq. : 
The “ Landes Oekonomie Collegium” at that time carried on 
systematic experiments in agriculture at fourteen distinct stations 
scattered through the Prussian domain. The trials which we 
now speak of, were made for the ostensible purpose of studying 
the exhaustion of the soil by cropping. The plan was to analyze 
