490 A. B. BEAUMONT 
In ceramics the practice of increasing or bringing back the plasticity 
of clays by keeping them soaked with water for several months is a common 
one. The effect of this aging as well as weathering may be the produc- 
tion of the colloidal condition by hydrolysis, according to Ries (1908). 
Mechanical grinding is often as efficacious as aging in improving plas- 
ticity. In this connection Rohland (1911) says: ‘By repeated moisten- 
ing with water the amount: of colloids is increased and thereby plasticity 
is raised.” 
Ruprecht and Morse (1917) show the positive presence of soluble salts 
of iron, aluminum, and manganese in soils long treated with ammonium 
sulfate, and it is to these soluble salts that toxicity is ascribed. Morse 
and Curry (1908) show that the presence of calcium carbonate prevents 
the formation of soluble iron and aluminum salts in soils treated with 
certain solutions. 
The soil from limed plats shows a greater adsorption for dyes than does 
that from unlimed plats (Ruprecht and Morse, 1915). This indicates 
more colloidal matter due to the liming. As pointed out by Ruprecht 
and Morse, this is probably due to a flocculation or a precipitation of the 
iron and aluminum in some form by the calcium compounds. If so, this 
presents a case of chemical reversibility which is of importance as regards 
the toxic effect cf ammonium sulfate long used as fertilizer. 
In the formation of iron-pan in moor soils, as cited by Warington (1900), 
a similar case of chemical reversibility of the colloidal condition is pre- 
sented. The iron passes into the soil as soluble salts and is later precipi- 
tated as colloidal ferric oxide. Under certain conditions this may again 
go into solution and the process be repeated. 
Summary of literature cited 
While the observations and the results of investigations that have been 
mentioned are more or less conflicting, it seems that the following points 
stand out: 
1. Previous drying of a soil is, in general, favorable to its fertility. 
2. Data have been obtained which show that this effect on fertility 
may be traced to physical, chemical, and biological causes. 
3. Drying and wetting some soils produces volume changes, and affects 
the water-holding capacity, the penetrability, and other physical 
properties. 
