44 



Journal of Agricultural Research 



Vol. V, No. I 



centage of salt, and the more molecules there are the greater -will be the 

 osmotic pressure, provided there is the same dissociation. Following out 

 this reasoning, a salt of low molecular weight should be more toxic than 

 one of higher molecular weight if the salts were present in the same per- 

 centage by weight. Indeed, in the study of osmosis, salts would not be 

 expressed in percentages but in molecular solutions. In soils, however, it 

 is impossible to express salts on a basis of molecular solution. 



In Table XV it will be seen that in a general way salts with low molecu- 

 lar weights are more toxic than those having a higher molecular weight, 

 but there are so many exceptions that this can not be considered a general 

 law holding for all salts. For example, magnesium sulphate has a lower 

 molecular weight than potassium sulphate, sodium sulphate, potassium 

 carbonate, or magnesium nitrate, and yet it is less toxic than any of 

 these salts. 



Table XV. — Comparison of the toxicity of the various salts with their molecular weight 



order of toxicity. 



Sodium chlorid 



Calcium chlorid 



Potassium chlorid 



Sodium nitrate 



Ammonium carbonate 

 Magnesium chlorid. .. 

 Potassium nitrate .... 

 Magnesium nitrate . . . 



Sodium carbonate. .. . 

 Potassium carbonate . 



Sodium sulphate 



Potassium sulphate. .. 



Magnesium sulphate. . 



.Number of 



plants 

 germinated. 



2-3 

 2.8 



3-1 



3-3 



3-3 

 3-4 

 3-9 

 4.6 



6.2 



6.4 

 7.0 



7- I 



7-9 



Weight of dry 



matter 



produced. 



Gm. 



O. 020 



.031 



. 040 



•035 



,044 



039 



,074 



,052 



,071 

 ,087 

 . 101 

 , lOI 



105 



Molecular 

 weight. 



58.5 

 III. O 

 74.6 

 85.x 



202. 2 



95-3 

 loi. 2 



148.4 



106. I 



138-3 

 142. 2 

 174.4 



120. 4 



SALTS ALONE AND IN COMBINATION WITH OTHER SALTS 



One of the most important questions arising in connection with the 

 toxicity of alkali is regarding the action of salts when present alone and 

 when in combination with other salts. Considerable work has been done 

 on the antagonistic action of various salts in solution cultures, and some 

 very remarkable results have been obtained; but many of these results 

 do not hold when the salts are applied to the soil. 



An examination of figures 2 to 24 will show that in the soil the antag- 

 onistic action of the various alkali salts is not so great as previous workers 

 have found for these same salts in solutions. For example, the magne- 

 sium salts when used alone in solution are very toxic to plants, but this 

 is largely overcome by the presence of other salts. The results for mag- 



