109 
PERCOLATION. 
The permeation of water through soils of different qualities has 
been studied by Welitschkowsky (Wollny, 1888, X, p. 2038.) He 
maintained a layer of water at a constant height above the material 
through which it permeated; therefore the pressure forcing the water 
through was constant. He found that the quantity of flow increased 
at first rapidly, then slowly for several days, depending on the thick- 
ness of the stratum of soil and the pressure of the water, until the 
permeation reached the maximum; then the rate of flow diminished 
slightly for a day or two until it became constant. He found that 
the quantity of water delivered in a unit of time has no simple rela- 
tion to the pressure forcing it through the soil or to the thickness of 
the layer of soil through which it flows, but the relation is more 
nearly expressed as follows: If the pressure be increased by regular 
additions the flow of water increases in an arithmetical progression 
such that the quantity equals (A) plus a constant factor (D) times 
the pressure (P) less unity; A+D (P—1). The numerical values 
of these terms can be deduced from his extensive tables of experi- 
ments, of which the following table is an abstract: 
Intensity of flow, in liters, per minute. 
Maxi-| Layer of soil 50cm. thick. | L@yer of soil 100 cm. 
. mum - thick. 
: Size of 
Soil. grains. capac- 
ey tor Head of water pressure. Head ot eter IWHES- 
10 cm. 50cm. | 100cm. | 10cm. | 50cm. | 100 cm. 
| 
mm. | 
ine sanders. soos so se 0.33 90.86 | 0.00013 | 0.00022 | 0.00081 |----_--- [eae ee | eteepemtcte 
AV erage Sand =! ©2322 2 a. 0.33-1.0 | 71.46} 0.106 0.179 0.273 | 0.096 | 0.126 0. 167 
@Woarse sand: -=2- 2. 2=24_3- | 1.0 -2.0 | 52.59 | 1.172 1. 886 2.776 1.011 | 1.349} 1.789 
Smaillieravel<.-:2.---=---- | 2.0 -4.0 | 19.37 | 6.747 | 9.594 13.1387 | 6.435 | 8.034 | 10.015 
Average gravel __...__-..-- | 4.0 -7.0| 13.44 | 11.708 GROL is ae eeee eee EOS IS robbs eeee 
«The capacity for water is expressed as a percentage of the weight of the dry soil. 
The general laws of the flow of waters through soils of different 
natures have been elaborately investigated by Milton Whitney in a 
series of papers published in Agricultural Science, Volume IV, to 
which the reader must refer for the details. 
The percolation of water through the soil, whether it goes down- 
ward as drainage or upward to be evaporated from the surface, 
depends not merely upon the degree of comminution of the soil and 
its compactness, but also, among other things, to a slight extent, upon 
the barometric pressure of the atmosphere, so that a falling barometer 
is, according to E. S. Goff, generally accompanied by a corresponding 
increase in the rate of drainage or of percolation downward. (Agr. 
pci:, Vole I pal (3.) 
