Nov. 4. i9i8 Soil Factors Affecting the Toxicity of Alkali 311 



used in the experiment. They were left standing in stoppered containers 

 for forty-eight hours. It was found that no regular results could be 

 obtained without this forty-eight-hour period of standing. The freezing 

 point was then determined by the method referred to above. From 

 solution experiments it was found that a gram-molecular solution of 

 sodium chlorid froze at —3.56° C, sodium carbonate at —4.58° C, 



naClin ppm- of dry soil 



-^00 1.000 2.000 J.OOO 4:000 



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mo/siure 



zov. 

 moisture 



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 moisture \^J^^l*Aj^J^lyK.:jK.lA^ 



• — ont plant "— ^= o-igm dry matter 



HqiCOj in p.p. m. of dry SOI I 

 SCO 1,000 J.000 Jjooo 7.000 10.000 



moisture ^k:*M2/<^j:)^^ 



so% 

 moisture 



2S% 



moisture 



J0% 



moisture 



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moisture 



zov. 

 moisture 



Z57. 



moisture 



J0% 



moisture 



DogSQ^ inp.pmof dry soil 



SOO 1.000 J,000 .5/300 7,000 10.000 



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• = one plant "^ =^ o.ifm dry metier 



Fig. 22.— Diagram showing the number of wheat plants up and the dry matter produced in 21 days in 

 sand and clay maintained at different moisture contents and containing sodium chlorid, sodium 

 carbonate, and sodium sulphate in various concentrations. 



and sodium sulphate at —4.37° C., the depression being directly pro- 

 portional to the concentration. With these figures it was possible to 

 calculate additional strength of the soil solution from the freezing point, 

 assuming it contained only the salt added. From this and the theoretical 

 strength, calculated from the amount of salt and water added, the rela- 

 tive adsorption of salt and of water could be calculated. It was found 

 necessary to use a check with each series for comparison, since some 



