390 



SOILS. 



tions renders this a perfectly simple and acceptable explanation. 

 Since these minerals are known to be incapable of crystalli- 

 zation, we are moreover led to the presumption that it will as a 

 rule be found in the finest portions of the soil, viz., in the 

 " clay " of mechanical analysis. 



Some illustrations of these conditions are given below, for soils from 

 Mississippi and California. The soluble silica being all assigned to 

 kaolinite, the rest of the alumina must be assumed to be present as 

 hydrate, since no other compound could fulfil the stoichiometrical re- 

 quirements. 1 The table therefore shows the differences between the 

 amounts of alumina found by analysis, and those assignable to kaolinite, 

 calculated to the mineral bauxite the most abundant, as well as the 

 one containing the medium proportion of water, among the three 

 naturally occurring aluminic hydrates. 



TABLE SHOWING EXCESS OF ALUMINA OVER SILICA IN SOILS ; CALCULATED AS 



BAUXITE. 



It is apparent from this table that if, as is probable, the aluminic 

 hydrate accumulates in the " clay " of the analysis, it will in some cases 

 form a very considerable percentage of the same, and detract to that 

 extent from its plastic, adhesive and other properties. But it must be 

 remembered that the assumption upon which this table is calculated, 

 leaves out of consideration the zeolitic portion, which as the 6th column 

 shows, is frequently quite large as measured by the bases found, to 



1 Since any complex zeolite would contain less alumina than kaolinite, this 

 assumption more than covers the possible zeolitic alumina. 



