excess.^ AVhy the corresponding^ calcium solution should also hinder 

 growtli can not be satisfactorih' explained at present. 



RESULTS WITH MIXED SOLUTIONS. 



Upon comparing the limits of endurance for lupine roots in pure 

 solutions of the ''alkali" salts with the limits determined by the 

 methods employed in a field survey, it became obvious that the for- 

 mer were vasth lower than the lattei-; and that furthermore the order 

 of toxicity of the several salts as fixed by investigators in the field 

 differed greatly from that obtained l)y experiments in the laboratory. 

 This was strikingly the case with magnesium sulphate, which is 

 decidedly the most toxic of the seven salts when alone in a pure 

 aqueous solution, but which is regarded as the least injurious bj^ 

 students of alkali soils. But it was recalled that none of these salts 

 usually occurs in any notable quantity in the soil save in the pres- 

 ence of one or several others, both of the readily soluble salts and of 

 the comparatively insoluble magnesium carbonate, calcium carbonate, 

 and calcium sulphate. The key to the discrepancy api:)eared there- 

 fore to lie in mixtures of the various salts, and the study of these 

 became, logically, the next step in the investigation. 



In exi)erimenting with mixed solutions it was jjlanned to test every 

 possible combination of two of the readilv soluble salts with which 

 experiments were made in jjure solutions. Another line of experi- 

 ments, from which were obtained results which are believed to be of 

 considerable scientific interest and from an economic point of view 

 to indicate one of the possible solutions of the alkali soil problem, con- 

 sisted in combining each of the readily soluble salts with each of 

 three difficultly soluble ones — calcium sulphate, calcium carbonate, 

 and magnesium carbonate. The only triple mixtures so far tried are 

 those of each readilj' soluble salt (except calcium chloride) with cal- 

 cium sulphate and calcium carbonate. Sodium bicarbonate was 

 tested only in this triple mixture. 



Although the work with mixtures of salts is by no means com- 



^ Treadwell and Renter [Zeit. flir anorg. Chem., 17, 199 (1898)] showed that at 

 15' C. and under a partial pressure of carbon dioxide in the vapor phase equal to 

 zero, pure water dissolves about 63 parts of magnesium carbonate per 100.000. 

 With a partial pressure of carbon dioxide In the vapor phase equal to one atmos- 

 phere there was dissolved about 1,211 parts magnesium hydrogen carbonate, 

 equivalent to 69S parts of the normal carbonate per 100.000 of solution, [t is thus 

 seen that the solubility is enormously increased by the presence of carbon dioxide. 

 Cameron and Briggs [Bui. 18, p. 22, Division of Soils. U. S. Department of Agricul- 

 ture (1900)] showed that a solution of magnesium carbonate in solution in equi- 

 librium with ordinary air contained about 18 parts of magnesium in 100.000 of 

 solution, which might have been expected to be enough to prohibit growth in view 

 of the toxicity of solutions of magnesium chloride and magnesium sulphate. It 

 should be further noted that it was shown that 6 parts of the dissolved magnesium 

 was combined as the normal carbonate, so that the solution contained more than 

 appreciable-amounts of OH ions, resulting from the hydrolysis of this latter salt. 



