502 SECTIONAL TRANSACTIONS.—M. 
grassland m the area show similar relationships; field observations being com- 
pared with maps derived from official statistics. 
In order to determine whether soil types so distinguished have an existence 
apart from the theoretical, and to show that the work has a practical bearing, 
2 Stra on grassland and arable land have been commenced on each type 
of soil. : 
8. Prof. SvEN Opren and Dr. B. A. Keen.—The Odén-Keen Appa- 
ratus for Automatic Mechanical Analysis. 
The mechanical analysis of soil is one of the fundamental operations of the 
soil scientist. It is, however, somewhat arbitrary, in that there is no general 
agreement on the sizes chosen for the various groups, and further, the repre- 
sentation of the soil as a mixture of a few fractions is not in accordance with 
facts. These anomalies may be removed, if we can by any experimental 
method construct a distribution curve connecting particle dimensions with the 
amount of particles corresponding to every size. 
There are five possible methods which can be used for this purpose. Starting 
with a soil suspension, which is completely deflocculated and dispersed, we- 
may measure (1) the change of specific gravity of the suspension with (a) depth 
or (>) time; (2) the change in hydrostatic pressure with (a) depth or (6) time; 
and (3) the rate of accumulation of particles on a plate suspended in the 
liquid. ‘The experimental difficulties are least in methods (2) (b) and (3). 
The former is illustrated by a modification of Wiegner’s apparatus 
and is most suitable for coarse and rapidly settling particles. The latter method 
is illustrated by the Odén-Keen automatic recording balance, which has been 
constructed in collaboration with the Cambridge-Paul Scientific Instrument 
Company. The suspended plate is attached to one arm of a balance, which is 
kept in equilibrium by an automatic adjustment of the current through a 
solenoid attracting a permanent magnet suspended from the second arm of 
the balance. When the weight of the sediment reaches a given amount—.e. 
when the solenoid current reaches a given value—a small metal sphere is 
automatically placed on the second pan of the balance, and the solenoid current 
returns to a smaller value. The strength of the current is recorded on a 
moving paper band, and the operation just described results in this curve 
presenting a series of steps. A very open and sensitive scale can, therefore, 
be used for the curve, although the actual trace is confined within narrow limits 
of width. The sensitiveness of the record can be modified or increased by suit- 
able adjustments of the component parts of the apparatus. The periodic 
replacement of the electro-magnetic attraction by the metal spheres results in 
the sensitiveness in any given experiment remaining constant. 
9. Mr. E. A. Fisuer.—Imbibitional Soil Water. 
Water is held by soil in two ways: by capillarity between the soil grains, 
and by imbibition within the material of the soil colloids. In sand, water is 
held by capillarity only. Sand does not swell appreciably while absorbing 
water; soil swells considerably. This swelling is due te imbibitional water. 
If xylol be substituted for water no swelling of soil occurs: xylol is held by 
capillarity only. If the moisture equivalent (ME) and the ‘ xylol equivalent ’ 
(XE) (calculated in a volume basis) are determined for sand the two 
values are identical; with soil ME—XE is considerable, and is a measure of 
the imbibitional water present. When ME is determined under different centri- 
fugal forces (f), ME plotted against 1/f is a straight line the slope of which 
measures the intrinsic swelling capacity of the soil colloids. 
These phenomena can be explained on the basis of a Donnan equilibrium. 
10. Prof. D. R. Hoacuanp and Dr. A. R. Davis.—Suggestions Con- 
cerning the Absorption of Ions by Plants in Relation to Soil 
Problems. 
In the afternoon an excursion to Wirral Farms took place. 
