72 REPORTS ON THE STATE OF SCIENCE.—1918. 
This view is found to account for all the phenomena as yet 
recorded. Moreover, it explains the difficulties that have 
attended the study of the soil solution or the liquid phase in the 
soil. Chemists now realise that the colloids profoundly affect the 
- composition of the liquid phase, and they are devoting consider- 
able time and ingenuity to the problem of extracting typical 
samples for investigation. Centrifugal methods have been tried, 
but they are troublesome in application. Displacement methods 
would be easier if one could be sure that the adsorption relation- 
ships were not being disturbed. Morgan claims that paraffin 
oil is both effective and simple in use. A pressure method is in 
use in Ramann’s and also in van Zyl’s laboratories, especially for 
soils containing much clay or humus: 3 kgms. of soil are sub- 
jected to a pressure of 300 kilos per sq. em. In view of the 
great importance of the soil solution in the nutrition of plants, it 
is a matter of vital necessity to discover the laws governing its 
composition, the influence of manuring, climate and_ soil 
treatment. 
Thus it is known that sodium salts liberate potassium from the 
soil: lime also has the same effect. Regarded as adsorption 
effects the phenomena are much easier to explain than as simple 
chemical reactions. The technical importance of a full under- 
standing of the phenomena is considerable. There is, however, 
a school of chemists who regard the whole phenomena as chemical, 
and adhere to the hypothesis of reactive zeolites: Gedrortz in 
Russia, and von Rothmund and Kornfeld in Germany, 
The action of Acids on the Sorl., 
Agricultural chemists have long hoped that soil analysis might 
guide the farmer in drawing up a system of manuring. Unfortu- 
nately, this hope has proved largely illusory; the problem is 
complicated by the fact that at least five or six factors enter into 
soil fertility, of which the chemical composition of the soil is 
only one. But there is another source of trouble well recognised 
by agricultural chemists: the selection of a method for the ex- 
traction of the plant nutrients in the analytical process. 
The first methods, founded wholly on mineral analysis, 
involved the use of strong acids and proved of little value in 
this country. A marked improvement was effected when dilute 
acids were substituted for strong acids, but many anomalous 
cases still arose: in particular, no two acids ever gave the same 
result, nor even did different concentrations of the same acid. 
The underlying assumption always was that the soil was a mass 
of mineral fragments with the phosphates, etc., in the ordinary 
mineral form. All attempts to interpret the action of dilute 
acids on soil phosphates as an ordinary chemical reaction failed. 
Russell and Prescott have studied the reaction between dilute 
acids and the phosphates in the soil and find that it can be inter- 
preted satisfactorily as a simple solvent followed by an 
adsorption. The solvent action is practically the same for nitric, 
hydrochloric and citric acids of equivalent strengths, and appears 
to be the normal action of an acid ona phosphate. The reverse 
