26 



BULLETIN" 122, U. S. DEPARTMENT OF AGRICULTURE. 



The method applied by them is as follows: Ten grams of the sample 

 were separated into sands of five different grades and into silts and 

 clays. The determinations were made on subsamples of very fine 

 sand (1-0.05 mm. diameter) and on the coarser silts (0.05-0.005 mm. 

 diameter). Six or eight counts were made on each sample, and from 

 the number of potash feldspars and micas and the total number of 

 particles present the percentages of the forenamed minerals have 

 been determined. 1 



From this data and from the amount of each separate in the soil 

 the minimum percentages of potash feldspars and muscovite have 

 been determined. The minerals in question in the coarser sands and 

 clays are not included, for these separates are difficult to examine. 

 The percentage of potash-bearing minerals in the clay is very often 

 higher than in any other separate, as shown by Failyer, Smith, and 

 Wade. 2 



Table V shows the relation between the total amount of potash in 

 the soil as shown by fusion analysis and that estimated from the 

 amount of potash minerals determined in the sands and coarse silts. 

 The theoretical 3 percentage of potash in orthoclase was taken as 

 the basis for calculation and 8 per cent was used for muscovite. . 



Table V. — Relation between the actual amount of potash present and the amount of 

 potash in the minerals estimated. 



Number 



Potash. 







of soil 





From min- 



sample. 



Actual. 



eralogical 

 data. 





Per cent. 



Per cent. 



1 



0.10 



0.22 



16 



.61 



.32 



19 



3.96 



2.33 



22 



4.07 



2.77 



Excepting sample No. 1, where the actual amount is small — and 

 for this reason the exception is not important — there is much more 

 potash present than is accounted for mineralogically. These figures 

 simply show that the estimates based on an examination of the min- 

 erals are certainly not too high. 



In all the soil types examined there were present either potash 

 feldspars or potash mica in large amounts. In one case only is 

 potash feldspar lacking and, likewise, muscovite was not found in one 



'In this calculation it is assumed that in each mechanical subdivision the average weight of the particles 

 of each mineral in question is equal to the average weight of the particles of any other mineral. While this 

 is not strictly true, it is sufficiently accurate for the purpose. The error is probably greatest in the mica 

 determinations. 



s Bui. 5-4, Bureau of Soils, U. S. Dept. Agriculture. 



• Orthoclase as ordinarily found does not contain the calculated amount of potash. 



