350 



SCIENCE 



[N. S. Vol. LIV. No. 1398 



and the effect of soluble fertilizer materials, 

 or between these different complexes in dif- 

 ferent soil types, but the way has been opened 

 for chemists now to study the soluble mineral 

 compounds in the nutritive solution of the 

 soil as never before. 



The following list of salts has been identi- 

 fied in soils, or obtained from soils through 

 the quiet evaporation of the dilute extracts 

 until crystals appear. 



Aphthitalite, 



Aragonite, 



Blodite, 



Borax, 



Caleite, 



Carnallite, 



Dolomite, 



Epsomite, 



Gaylussite, 



Gypsum, 



Halite, 



Hanksite, 



Kainite, 



Kieserite, 



Langbeinite, 



Leonite, 

 Loweite, 

 Magnesite, 

 Mirabilite, 

 Natrolite, 

 Northupite, 

 Pieromerite, 

 Soda niter, 

 Sodium carbonate, 

 Sulphohalite, 

 Sylvite, 

 Thenardite, 

 Thermonatrite, 

 Tri-sodium phosphate, 

 Trona, 

 Vanthoffite. 



COLLOIDAL CHEillSTRY — THE ULTRA CLAY 



This brings us down to the fourth great 

 fundamental line of research which completes 

 the outline of the problems to consider in 

 future soil investigations and the most diffi- 

 cult of all to understand. 



Always in our study of the texture of the 

 soil, we have realized that there was some- 

 thing which modified the texture, something 

 that bound the grains of soil together making 

 certain soils very plastic when wet and very 

 hard compact when dry and making other soils 

 more friable and even incoherent when dry. 

 It took us a long while to determine the cause 

 of this plasticity. It was something that went 

 obviously into solution but did not have the 

 properties of a true solution. Finally we 

 were able to separate it and found that it was 

 a colloidal solution. From this we have pre- 

 pared and collected the colloid itself, to which 

 we have given the name ultra clay. The ex- 

 amination of this material leads us into the 

 realrii of colloidal chemistry which is a most 



difficult field to investigate because of the ex- 

 tremely inert nature of all materials in a 

 colloidal state. 



This ultra clay when dry will absorb as 

 much as 200 times its volume of ammonia 

 gas, from 20 to 40 per cent, of its weight of 

 water vapor in a closed space over free water 

 at 30° C. and in a wet state will absorb from 

 10 to 30 per cent, of its weight of certain 

 dyes. By heating the ultra clay or an ordin- 

 ary soil to 900 to 1000° C. this absorptive 

 power is practically completely killed. By 

 measuring the absorption of water vapor, of 

 ammonia, and of certain dyes in the original 

 soil, in the killed soil, and in the ultra clay 

 separated from the soil, we have been able 

 to estimate the amount of ultra clay in soils. 



This ultra clay is as strong in its power to 

 cement sand grains as is Portland cement, 

 but when a dry briquette cemented by ultra 

 clay is put into water it goes to pieces while 

 a similar briquette of Portland cement holds 

 its shape and crushing strength. When soil 

 is heated to 900 or 1000° 0. it loses almost 

 completely its binding power when formed 

 into a briquette, but if the amount of colloid 

 estimated to be present by the methods 

 already referred to is added to the killed 

 soil the original plasticity is restored and the 

 crushing strength of the dry briquette is 

 about the same as in the original soil. 



This colloidal material is disseminated 

 through the soil as a film over the mineral 

 grains, giving plasticity to the soil when wet, 

 and hardness to the soil when dry, and is the 

 medium for the absorption of gases, of 

 organic, and of mineral matters. Physically 

 it is analogous to the muscles and tendons 

 of the animal body, which permits the articu- 

 lation and motion of the skeleton and its 

 fleshy covering in the animal; chemically it 

 is analogous to the lining of the stomach and 

 other digestive and respiratory organs of the 

 animal and of the protoplasmic content of 

 the vegetable cell. It appears to be essential- 

 ly a silicate of aluminum and iron. We 

 have not as yet been able to determine whether 

 the small amount of lime, magnesia, potash, 

 and soda present are a part of its constitution 



