44 



be improved by treating it with carbon black, as sug- 

 gested by the work of Scheiner (16). In this work 

 washed carbon black was used at the rate of 10 grams 

 per liter and filtered out. 



Again, the extract was distilled in an effort to de- 

 termine if any volatile toxic bodies were present. The 

 distillation was done in the following manner: 500 

 cc. of the extract was placed in a Jena flask connected 

 with a glass condenser, and distilled until the distillate 

 amounted to 185 cc. Both the residue and the distil- 

 late were then made to 1,000 cc with distilled water. 

 Still another portion of the extract was evaporated to 

 dryness, burned to a red heat in a porcelain dish, the 

 mineral residue taken up with HCl, and evaporated 

 to dryness on the w^ater bath. A little water was add- 

 ed, and the salt again evaporated to dryness, after 

 which the dish was heated at about 100" C. until no 

 trace of free acid could be detected. This salt was 

 then taken up with distilled water and made to vol- 

 ume. The extract that was precipitated was made 

 alkaline with NaOH, the precipitate filtered out and 

 H2SO4 added until the solution was slightly acid. 

 Then a slight excess of c. p. CaCOo was added to ])ring 

 the solution back to neutral. The sorghum cultures 

 grown in these solutions were started May 15, and tak- 

 en down June 5, 1917. The data are set forth in Table 

 III, and photographs are given in Plate I, fig. 2. 



Table III.— The Effect of Carbon Black, Distillation, 

 Precipitation, and Ignition on the Toxicity of a 

 Soil Extract Containing a High Concentra- 

 tion of NOl, and Mn. 



Culture Medium 



Distilled water 



Soil extract 50 per cent, dist. water 50 per 



cent, precipitated 



Soil extract 25 per cent, dist. water 75 per 



cent, precipitated 



Volatile part of soil extract 50 per cent, dist. 



water 50 per cent 



Non-volatile part of soil extract 50 per cent, 



dist. water 50 per cent 



Soil extract 50 per cent, dist. water 50 per 



cent, plus carbon black 



Soil extract ashed, 50 per cent, dist. water 



50 per cent 



Dist. water plus carbon black 



Soil extract 50 per cent, dist. water 50 per cent 

 Soil extract 25 per cent, dist. water 75 per cent 



Av. air drv wt of 



