35 



corrosion due presumably to the action of hydroxyl ions, while a 

 smaller number survived in apparently perfect condition, and this 

 occurred in repeated experiments. In critical solutions of other salts 

 and mixtures of salts j however, there was rarely such sharp differ- 

 ence in appearance between roots which survived and those which 

 died during twenty- four hours' culture; as a rule none of the roots 

 were in normal condition at the end of the experiment. In other 

 words, the difference of individual plants in their i)ower to resist toxic 

 action appears to be more pronounced in the case of the two carbonates 

 of sodium than of other "alkali salts." This would indicate that the 

 selection of plants for resistance to "black alkali" offers a simpler 

 problem than where resistance to other components of alkali soils is 

 to be sought. 



SODIUM SULPHATE IN MIXTURES. 



Experiments with sodium sulphate in mixtures with other salts 

 show the following results: 



Table VII. — Limits for sodium sulphate in mixtures. 



Name of salt added. 



None 



Sodium chloride 



Calcium chloride 



Magnesium (rarbonate 



Calcium carbonate 



Calcium sulphate 



Calcium sulphate and calcium carbonate a — 



Greatest endurable 

 concentration of 

 sodium sulphate. 



In frac- 

 tions of a 



normal 

 solution. 



0.0075 

 .00375 

 .2 

 .03 

 .04 

 .5 

 .3 



In parts 

 per 100.000 

 of solution. 



53 

 26. 



1,272 



212 



281 



3,530 



1,908 



Concentration of the 

 salts added. 



In fractions 



of a normal 



solution. 



0.01 

 .2 

 Saturated. 

 Saturated. 

 Saturated. 

 Saturated. 



In parts per 

 lon,fXJ0 of 

 solution. 



58 

 1,102 

 Saturated. 

 Saturated. 

 Satui-ated. 

 Saturated. 



a See Bui. 17., p. 22 et seq., Division of Soils, U. S. Department of Agriculture, 1901. 



Sodium sulphate is very abundant in "alkali" soils, often occurring 

 in contact with each or several of the other salts. In the Billings, 

 Mont., type, for example, it is accompanied by the sulphates of mag- 

 nesium and calcium, while in the Fresno, Cal., type it is in contact with 

 sodium carbonate. 



Most effective for neutralizing this salt is calcium sulphate, which 

 raises the limit more than sixty times when added alone. In the 

 presence of an excess of calcium carbonate, however, calcium sul- 

 phate can increase the limit of endurance for sodium sulphate only 

 about fortj^ times. This is probably due to a forcing back of the dis- 

 sociation and decrease of solubility of the calcium sulphate b}^ the 

 calcium carbonate, although, as Cameron and Seidell ^ have shown, 

 either salt is rather soluble in dilute solutions of sodium sulphate. 



' Solution Studies of Salts Occurring in Alkali Soils, Bui. 18, Division of Soils, 

 U. S. Department of Agriculture. 



