14 



BULLETIN 551, U. S. DEPARTMENT OF AGRICULTURE. 



of Huston fine sandy loam differ markedly in iron, alumina, and sulphur. 

 Still further, on comparison of soils of different types, it is possible 

 to choose two or more that agree quite as closely as any two of the 

 same type. This is brought out in Table 7. 



Table 7. 



-Variation in the chemical composition of soils of the same texture but of differ- 

 ent series. 



Type. 



Si0 2 . 



Fe 2 3 . 



AI2O3. 



CaO. 



MgO. 



K 2 0. 



Na 2 0. 



P2O5. 



SO3. 



Norfolk fine sandy loam 



Huston fine sandy loam 



Tifton fine sandy loam 



Portsmouth fine sandy loam . 



Per ct. 

 95.54 

 95.51 

 94. 15 

 94. S5 

 80. IS 

 79.35 

 71.38 

 70.99 



Per ct. 



0.62 



.68 



.94 



.41 



3.05 



4.44 



3.63 



4.23 



Per ct. 

 1.70 

 1.70 

 1.67 

 1.37 

 8.48 

 8.89 

 12.29 

 11.39 



Per ct. 



0.06 



.12 



.05 

 Trace. 

 .27 

 .63 

 1.09 

 .93 



Per ct. 



Trace. 



Trace. 



■Trace. 



Trace. 



0.45 



.39 



.36 



1.08 



Per ct. 



0-06 

 • 16 

 .10 

 .06 



1.84 

 .67 



2.28 



2.71 



Per ct. 



0.18 



.04 



Trace. 



.06 



.72 



.24 



1.14 



.82 



Per ct. 

 0.05 

 .04 

 .04 

 .05 

 .10 

 .18 

 .10 

 .19 



Per ct. 

 0.03 

 .23 

 .06 

 .03 

 .03 





.13 





.18 





.39 







Probably no one has ever seriously contemplated classifying soils 

 on the basis of their chemical composition alone, but it seems probable 

 that soils that are alike in color, texture, relation of soil to subsoil, 

 and formed by the same agencies, in other words, having such similar 

 characteristics that they would be given the same type name by 

 field observers, should have some chemical resemblance. The soils 

 just compared, the analyses of which are more or less alike, are soils 

 that because of characteristics other than texture have been given 

 distinct type names; but how wide the variation of a single type may 

 be in chemical composition, or whether some types should be sepa- 

 rated into two or more because of chemical differences, or two or more 

 types amalgamated because of chemical resemblances, is a matter for 

 future investigation. 



LIMIT OF ERROR IN ANALYTICAL WORK. 



Earlier in the paper the authors stated what they considered the 

 limit of error in the analytical work involved in the analyses here 

 presented and discussed. It was stated that what was meant by 

 limit of error was the allowable variation in results obtained from the 

 same sample by two analysts familiar with the method used. 



Several factors may contribute to this error: Lack of uniformity 

 of sample, impure reagents, contamination from glassware or other 

 utensils, and, finally, the error incident to the method, which may be 

 of both a personal and chemical nature. All except the last may be 

 nearly eliminated by care and blank determinations. 



All analytical results are a compromise, usually arrived at by 

 taking advantage of the solubility of compounds to be removed 

 and the relative insolubility of the compound to be recovered and 

 determined. No compound is absolutely insoluble, and when rela- 



