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 <rf 
these salts. 
Table XV .—Comparison of the toxicity of the various salts with their molecular weight 
Salts in order of toxicity. 
Number of 
plants 
germinated. 
Weight of dry 
matter 
produced. 
Molecular 
weight. 
Sodium chlorid .. 
2. 2 
Gm . 
0. 020 
. Oil 
58.5 
III. O 
Calcium chlorid . 
2.8 
Potassium chlorid. 
X. I 
• '■'O* 
. 040 
. ox s 
74.6 
85.1 
Sodium nitrate.. 
O’ * 
2 . X 
0 0 
Ammonium carbonate. 
3-3 
3-4 
.044 
. 010 
202. 2 
OC. X 
Magnesium chlorid. 
Potassium nitrate. . 
• w .)y 
. 074 
/J 0 
IOI. 2 
148.4 
Magnesium nitrate . 
o* y 
4. 6 
. OE2 
T w 
Sodium carbonate . 
6. 2 
. 071 
. 087 
. IOI 
106. I 
138.3 
I42. 2 
Potassium carbonate . 
6 . 4 
Sodium sulphate .. 
7.0 
7 -1 
Potassium sulphate . 
. IOI 
T *7 A , A 
Magnesium sulphate . 
7-9 
. IOC 
120. 4 
* J 
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- 
