Feb. II. 1918 Effect of Season and Crop Growth on Soil Extract 327 



Table III. — Analysis {in parts per million) of dilute, average, and strong solutions 

 by the methods outlined in United States Department of Agriculture Bureau of Soils 

 Bulletin ji 



The determination of magnesium, though it is the same procedure as 

 used for phosphate, has, at least in this series, given more accurate 

 results. The same standard solution is used in this method as in the 

 phosphate determination, and has a value approximately one-fourth as 

 great when expressed in terms of magnesium, a fact which would decidedly 

 tend to reduce the percentage of error in the final result. The same 

 colorimetric procedure for magnesium is still in use, as no more satis- 

 factory method for small amounts of this element has so far been 

 developed. The sulphate determination is seen to be more accurate 

 than that of calcium, but the error in low concentrations is from 35 to 

 85 per cent. This procedure has therefore been dropped and the sulphate 

 determinations are not included in the 191 5 charts. 



In planning the work for 1 916 it was evident that a smaller number of 

 more accurate determinations were to be preferred to a larger number 

 on which little reliance could be placed. With this idea in mind, work 



