96 
INVESTIGATIONS ON ROTHAMSTED SOILS. 
In England, however, with its high rents and its local land burdens 
and its fixed policy of free trade, which throws open our granaries to 
be filled by your good selves and our other cousins in other quarters 
of the globe, continuous wheat growing is no longer one of the direc- 
tions in which our farmers can afford to use the freedom which has 
succeeded to the old restrictive farming. But for you continuous 
wheal growing must for a long time remain an economic possibility. 
The gradual reduction of your soils in nitrogenous fertility is slow, 
and, as necessit}^ arises, can be amply met, as long as coal and nitrate 
of soda are abundant. We do not appear to be yet within sight of 
t lie end of the great nitrate deposits, and coal yields an increasing 
quantity of the other great concentrated nitrogenous fertilizer, 
ammonium sulphate; and there are, especially owing to your exten- 
sive animal and other industries, a great variety of other nitrogenous 
fertilizers, individually less concentrated, but of great aggregate 
quantity. 
Some day, when the nitrate is all gone and the coal is used up, you 
may perhaps realize the prophec}^ of Sir William Crookes, and make 
" electric nitrate " (we already make " electric soda") from the nitro- 
gen and oxygen of the air, using presumably tidal force, if j T our 
Niagara be too small, for generating the electricity needed to bring 
about the combination. But this is a dream of the very distant future. 
MINERAL ELEMENTS OF FERTILITY. 
We have been thus far mainly engaged, except for occasional 
digressions, in discussing questions relating to the supply and removal 
of nitrogen under various conditions. I would now direct your atten- 
tion to the results of certain investigations into the quantity and 
condition of the phosphoric acid and potash contents of the various 
plats of t his historic field. 
Throughout the duration of the experiments, numerous ash analyses 
have been made of the crops, and the supply and removal of both 
phosphoric acid and potash with regard to most of the plats can be 
estimated with some reasonable approach to accuracy. 
Until lately, however, no systematic series of determinations of 
phosphoric acid and potash have been made in the soils themselves. 
In L894 tin 1 present lecturer had the honor to contribute a paper "On 
the determination of probably available 'mineral' plant Pood in 
soils, 11 ' in which the use of a 1 per cent solution of citric re-id was 
proposed as a means of approximate differentiation by means of 
analysis between the total and the probably available phosphoric acid 
and potash in soils. 
Journal of the Chemical Society, London, C5 (1N94), pp. 115-107. 
