RESULTS WITH MIXED SOLUTIONS. 



15 



% NEUTRALIZING EFFECT OF AN EXCESS OF CALCIUM SULPHATE. 



Table VIII gives the critical concentrations of solutions for eight 

 different plant species in the presence of an excess of calcium sul- 

 phate. In the case of Lupinus alius, Medicago sativa, and Zea mays 

 these have been worked out with all six of the salts used in the 

 experiments with pure solutions, while for the other species only the 

 limits for magnesium chlorid, sodium carbonate, and sodium chlorid 

 were ascertained. 



Table VIII. — Critical concentration for seedlings of various plants in mixed salt solutions 

 (containing an excess of calcium sulphate), expressed in fractions of a normal solution. 



[The figures represent the critical concentrations for the more toxic salts, to which the calcium 



sulphate was added.] 





Plants used. * 



Salts used (each 

 mixed with an 

 excess of calcium 

 sulphate). . 



Lupinus 



albusf 

 (white 

 lupine) . 



Medicago 



sativa 

 (alfalfa). 



Zea mays ™icum 

 < maiz ^ (whfat). 



Andro- 



pogon 



sorghum 



(sor- 

 ghum). 



Avena 



sativa 

 (oats). 



Gossyp- 

 ium bar- 



badense 

 (cotton). 



Beta 



vulgaris 

 (beets). 



>fgS0 4 



0.4 

 .2 

 .03 

 .3 

 .2 

 .05 



0.35+ 



.2 ± 

 .02 

 .3 

 .2 



.08 



0.6 











MgCL, 



. 3 0. 225 

 . 05 . 0275 

 .4 -+- 



0.2 

 . 0225 



0. 175 

 .1025 



0.25 

 . 0275 



0.2 



Na2C0 3 



.05 



NaoS0 4 





NaCl 



.25 .2 

 .1 + 



.15 



.175 



.2 



.2 



NaHC0 3 

















*The varieties are in all cases the same as those used in obtaining the corresponding limits in pure 

 solutions (see Table VI. page 12). 



f Using the fresh lot of seed which gave so much higher limits in pure solutions (see note to table, 

 page 12), Harter repeated the experiments made by Kearney and Cameron with Lupinus albus in 

 mixed solutions. In the presence of calcium sulphate, however, Harter' s results agree closely with 

 those obtained by Kearney and Cameron (given in Table VIII, column 2) the critical concentrations 

 as determined by Harter being as follows: Magnesium sulphate, 0.35 normal; magnesium chlorid, 

 0.25 normal; sodium carbonate, 0.0375 normal: sodium sulphate, 0.25 normal; sodium chlorid, 0.175 

 normal; sodium bicarbonate, 0.058 normal. 



In comparing the limits in mixed solutions as stated in the above 

 table with those in pure solutions (Table VI, page 12), we notice 

 that the order of toxicity of the different salts is considerably altered 

 by the addition of calcium sulphate, sodium carbonate being in every 

 case the one that becomes most toxic, while the critical concentrations 

 of the sulphate and chlorid of magnesium become in all cases higher 

 than those of the sodium salts except the sulphate. The neutralizing 

 effect of calcium sulphate is therefore much more marked toward 

 the magnesium than toward the sodium salts. 



The presence of calcium sulphate tends very greatly to diminish not 

 only the differences between different species as to their tolerance 

 of the magnesium and sodium salts, but also the differences between 

 the latter in their toxicity to the same species. The first effect is most 

 strikingly illustrated by the limits for maize and white lupine in the 

 presence of magnesium sulphate. The former will endure a concen- 

 tration of this salt in pure solution from thirty-six to two hundred 

 times as great as is tolerated by the latter. But when an excess of 

 calcium sulphate is added the critical concentration for maize is less 



113 



