182 Causes of Fertility or Barrenness of Soils. 
Davy, who found that 1000 lbs. of the following, when tho- 
roughly dried, gained by exposure to a moist atmosphere — 
lbs. 
In the case of a I'ertilo soil, East Loihian 18 
,, ,, Somersetshire 16 
Soil from Mcrsca in Essex, worth 25s. an acre .. .. 13 
Sandy soil from Essex, worth 28.s. an acre 11 
Coarse sand, worth only 15.s. an acre 8 
Soil i'rom Bagshot Heath (uncultivated) 3 
The power of absorbing gaseous matters, such as carbonic acid, 
nitric acid, and ammonia, from the atmosphere, generally coin- 
cides with the quality of absorbing moisture, and therefore, though 
probably depending more upon chemical than mechanical agency, 
may be noticed here. The property of retaining moisture, which 
is valuable according to climatic circumstances, also appears to 
bear a close relation to the power of absorption. The following 
table has been obtained by taking equal weights of various soils, 
thoroughly drying, and adding water till each commenced drip- 
ping, then re-weighing the addition, of course showing the relative 
retentive powers of each ; thus — 
100 lbs. of pure clay became 170 lbs., thus gainings 70 lbs. 
100 „ clav loam 150 „ 50 „ 
100 „ chalk 145 „ 45 „ 
100 „ loamy sand 140 „ 40 „ 
100 calcareous sand 129 ,, 29 „ 
100 „ pure sand 125 „ 25 „ 
The power of retaining moisture depends in a great measure 
upon the state of mechanical division of the atoms of the soil : 
thus a coarse sand, according to Schubler, only retains 20 per 
cent, of water, while a fine sand can hold 40 per cent. The same 
thing is seen in the case of fine or coarse calcareous soils. Humus 
is one of the best absorbents and retainers of moisture. A pure 
vegetable soil, formed by decay of wood, is capable of absorbing 
200 and even in some instances 300 per cent, of moisture. The 
cohesive property is owing to the extremely fine state of the 
particles, and their attraction for each other increased by the 
presence of moisture. The amount or intensity of this quality in 
a soil is determined by the power required to separate a given 
mass. Schubler has found that taking the resistance or cohesive- 
ness of pure clay as 100 — 
Sand 0 
Fine lime 5 
Humus 8 
Sandy clay 57* 3 
Loamy clay G8*8 
Arable soil 33-0 
The difficulty of working clay soils is thereibre owing to the 
resistance offered to the implement by the cohesive attraction of 
