326 SOILS. 



The next step was to use in soil analysis acids of such strength as to 

 dissolve all the zeolitic (and water-soluble) portion, leaving the un- 

 weathered soil minerals behind ; it being assumed that the prolonged 

 action of the roots and soil-solvents would in the end act similarly to 

 the acids employed, such as chlorhydric or nitric acids. 



But here also the results of analysis very commonly failed to cor- 

 respond to cultural experience in the case of cultivated soils ; which 

 frequently failed utterly to produce satisfactory crops even when the 

 acid-analysis had shown an abundance of plant-food ingredients. Upon 

 this evidence, this method of soil investigation was also condemned as 

 being of little or no practical utility ; and this has ever since been a 

 widely prevalent view. 



The preferable investigation of cultivated soils was due to 

 the fact that they are practically the only ones available in the 

 countries where the study of agricultural science was then 

 being prosecuted ; and the paucity of useful results there 

 achieved discouraged the undertaking of similar researches 

 where, as in the United States, the materials for the investiga- 

 tion of the simpler cases those of unchanged, natural or 

 virgin soils were readily accessible. It was not apparent on 

 the surface that the indefinitely varied conditions introduced 

 by long culture would inevitably cause this lack of definite 

 correlation between the immediate productive capacity of a 

 soil and the composition of its acid-soluble portion, and that 

 yet the same might not be true of natural, uncultivated soils, 

 which have all been subjected, alike, only to the natural pro- 

 cesses of weathering, and t<> the annual return of nearly the 

 whole of the ingredients withdrawn by plant growth. 



Following the failure of the treatment with strong acids to 

 yield with cultivated soils results definitely correlated with 

 cultural experience, numerous attempts were made to gain 

 better indications by the employment of weaker acid solvents. 

 The pure arbitrariness of such diluted solvents was equaled 

 by the total indefiniteness and irrelevance of the results with 

 different soils. Only two rational alternatives seem to re- 

 main, viz., either to push the extraction to the full extent be- 

 yond which action becomes so slow as to clearly exclude any 

 farther effective action of plant acids; or else to use the latter 

 themselves at such strengths as by actual experiment is found 



