»9°9] DACHNOWSKI—BOG TOXINS 3g9 



show conclusively that the retention is not due to chemical fixation or 

 substitution. The amount of solution thrown out of the quartz by 



r mm 



me centrnugal machine was too small to be tested. A priori, it 

 would seem that the filter used should be markedly more toxic now 

 than the solution, when tested by physiological criteria. The pres- 

 ence of the adsorbed bodies in the solid should not only reduce its 

 effectiveness when repeatedly used for improving bog water, but should 

 replace normal growth by an abnormal retardation judged from the 

 growth-rate made in a similar check soil culture. 



To obtain evidence on this point, and to contrast the efficiency of 

 the various constituents of agricultural soils for adsorption, a series 

 of experiments was made with quartz, river sand, field clay, and humus 

 soil. The air-dry soils were sifted through a sieve with meshes of 

 Portions of 400" of the sifted soils were each placed in glass-stoppered 

 jars containing 1200" of bog water. The glassware employed in all 

 of the experiments cited was treated with a solution of potassium 

 dichromate and sulfuric acid, and repeatedly rinsed in distilled water 

 previous to use. The mixtures of bog water and soil were left stand- 

 mg in the dark room for three days. To insure thorough contact 

 between the bog water and the soil, the solution was occasionally 

 shaken. When ready for use the liquid was filtered off, and portions 

 or 4oo cc of the liquid from each soil type were used a's water-culture 

 experiments in the manner described above. For the investigation 

 on the relative fertility of the soils used as filters, earthenware pots 

 w ere used. The pots were new and each of about 300" capacity 

 (8 m in diameter, 8.$ cm deep). They were thoroughly cleaned and 

 dned in an oven at no° C, and later immersed in heated paraffin. 



each paraffined pot was added 200 cc of the contaminated soil 

 WeJ l pressed into the bottom and sides of the pots. It was recognized 



a t difficulties of obtaining good contact between the soil and the 



is °f the pot would be probable. In the air space along the walls 



usually by far the greater proportion of plant roots are developed, 



and ^e wire-basket method as recommended by the Bureau of Soils 



° the U. S. Department of Agriculture (Bull. 23) is, therefore, more 



Arable. But the form of retainer here described was found to be 



<% satisfactory. In no case were evidences found of roots growing 



m °re freely at the sides of the pot than in the center. The experi- 



