VARIATION IN THE CHEMICAL COMPOSITION OF SOILS. 11 



The extremes in composition with regard to major constituents are 

 as follows : 



Per cent. 



Silica, Si0 2 97. 01 to 44. 15 



Iron, Fe 2 3 '. 16. 23 to 0. 33 



Alumina, A1 2 3 27. 58 to 1. 19 



Potash, K 2 4. 07 to 0. 02 



Soda, Na 2 6 2. 06 to 0. 01 



Lime, CaO 1.73 to 0.01 



Magnesia, MgO 1.93 to 0.01 



Phosphoric acid, P 2 5 0. 22 to 0. 03 



Sulphuric acid, SO s 0. 34 to 0. 02 



There were 9 samples in which there were but traces (less than 

 0.01 per cent) of soda, 13 with but traces of magnesia, and 4 with 

 but traces of lime. 



In discussing the extreme variation shown in the samples analyzed 

 the authors wish to avail themselves of general information they have 

 regarding soil composition, based on partial analyses of other samples 

 not here reported, and hold to the following opinion: 



The maximum and minimum figures for silica, iron, and alumina 

 stated above, while probably not the maximum or minimum of soils 

 of the United States, are probably nearly so, and soils exceeding this 

 maximum or not reaching this minimum in content of these con- 

 stituents are not often met, except in the case of quartz sands on 

 the one hand and muck soils on the other. 



With regard to potash the same statement applies, although to a 

 less extent. No soils have been encountered in these laboratories 

 having less than 0.01 per cent K 2 0, and while there are soils con- 

 taining more than 5.0 per cent K 2 they are not common. 



Less is known regarding the true maximum and minimum of soda 

 content, for the reason that so few soils have been completely analyzed 

 and there are few available data for this constituent. It is probable 

 that in humid regions the maximum soda content of soils is consid- 

 erably less than that of potash, and instances where but traces are 

 present are not uncommon. 



The results for lime and magnesia, while representing the minimum, 

 are far from the maximum. Soils derived from calcareous material 

 and as yet unleached may, of course, be very high in both lime and 

 magnesia content, but even where there is little or no carbonate 

 present the total content of lime and magnesia may each be above 5 

 per cent. 



The figures for phosphoric acid do not represent the maximum or 

 minimum. It is not uncommon to encounter soils containing 0.01 

 per cent, and soils containing as high as 0.8 per cent are often found, 

 although generally confined to small areas. 



The knowledge of the total sulphur content of soils is not extensive 

 enough to make any general statement regarding the maximum and 

 minimum content. 



