August 27, 1920] 



SCIENCE 



199 



and by the conductivity method. It is evi- 

 dent from these results that in discussing the 

 toxic limits of alkali it will be necessary to 

 state the method used, the same as in dis- 

 cussing the amount of phosphoric acid in the 

 soil it is necessary to say whether the soil was 

 extracted with weak citric acid, weak hydro- 

 chloric acid, or fused. The result will vary 

 with the method of extraction. 



Mr. Headley mentions several times that we 

 have made no analyses and consequently we 

 do not know what the soil contains. As a 

 matter of fact, we have made thousands of 

 analyses of soils after adding salts to them as 

 well as soils direct from the field. In one of 

 the papers mentioned by him^ we have given 

 four tables aggregating about 650 determina- 

 tions to show the relation of " salts added " 

 to " salts recovered " by extraction and as 

 determined by depression of the freezing 

 point. 



In Utah Station Bulletin No. 170 we have 

 given the following table: 



the sulfates very much more was recovered 

 than was added. This came largely from cal- 

 cium sulfate which was present in the soil 

 and which was leached out by the compara- 

 tively large quantities of water used in 

 extracting the soil. In the soil itself the 

 calcium sulfate is not sufficiently soluble to 

 cause injury to plants; hence, it should be 

 subtracted from the total sulfates obtained. 

 In the case of the sulfates the " salts added " 

 are doubtless a more reliable index to the real 

 concentration of the soil solution than the 

 " salts recovered." 



With the carbonates it will be seen that 

 only a part of the salts added could be re- 

 covered by extraction. This means that in 

 the case of carbonates a correction factor 

 must be used for the " salts added," although 

 this in many cases is probably just as satis- 

 factory as to use " salts recovered." 



Even though we have in all our work had 

 available data on " salts recovered," we have 

 in many cases preferred to indicate the con- 



TABLE I 



Peroeniages of Salt Added to Boili Determined ly Water Extraction 



This table shows that practically all of the 

 chlorids and sulfates added could be recovered 

 by leaching. In the lower concentrations 

 additional salts, which were originally present 

 in the soil, were recovered. In the case of 



1 Journal Agricultural Besearch, Vol. 15, pp. 

 287-319. 



oentration by " salts added," since the former 

 method of expression is open to some rather 

 serious objections which it is probably un- 

 necessary to point out here. 



We hope that this will clear up any mis- 

 understanding of our work, for we believe 

 that while " salts added " does not tell the 



