THK HKOADHALK WHEAT SOILS. 
1)7 
As I lie chemists of your country were good enough to take a great 
deal of interest in this paper, and to subject the citric-acid process to 
further investigation and to make it the point of departure for a 
number of alternative processes — some of which, no doubt, are better 
applicable to some kinds of soils and others toother kinds — I need 
not now say more about the inception of the process than to recall to 
you that it was t he result of an attempt to imitate, in the solvent used, 
the acidity <>f the root-sap of flowering plants. This acidity was 
Determined in LOO plants, representing some twenty different natural 
orders. 
In oi-der to test the proposed method it was applied to a large num- 
ber of samples of soil from t he cont inuous barley plat s at Rothamsted, 
which bad been preserved under very various manorial conditions 
for over forty years. The results of this investigation were referred 
fo by Sir Henry Gilbert in his lectures to you, and he mentioned that 
I was then engaged in extending the investigation to the examination 
of the soils of the Broadball wheat plats. A number of the most 
typical plats were selected for this purpose, and the samples repre- 
senting the first three depths, drawn in l were examined, as well as 
corresponding samples, where these were available, drawn in lSn7> and 
1881. In all of these samples the total phosporic acid has been deter- 
mined, and also the potash dissolved under certain conditions by 
prong hydrochloric aeid. The quantities of phosphoric acid and 
potash dissolved by a 1 per cent solution of citric acid under the con- 
ditions originally laid down in my paper have also been determined. 
The results are fully discussed in a paper presented to the Royal 
Society of London. 
As in considering the nitrogen results we have thus far confined 
our attent ion to t he samples drawn in 1 *'.».*>, I will here follow the same 
procedure and will in like manner record the phosphoric acid and 
potash results for the 1803 samples, reserving nntil later a compari- 
son between the newer and the older samples. 
The accompanying table shows in a convenient form, for the series 
of plats submitted to mineral examination, tin' average yield of the 
plats as regards both grain and straw for forty- two yea rs, 1852-1893, 
and for the six years 1SS!>-1S!)4; and also the (plant ities of phosphoric 
acid and potash applied to the soil during fifty years in the form of 
manure, and the quantities removed in the crops during the same 
period. 
