[ 
THE Errect oF MANGANESE COMPOUNDS ON SOILS AND PLANTS 389 
The tube was shaken for exactly one-half minute and was then placed in 
the centrifuge, which was started one minute after the solution was added. 
At the end of two minutes the electric current was turned off the centrifuge, 
and the speed was allowed to decrease gradually while a second test was 
started. Five minutes after the aloin was added in the first test, a 
portion of the supernatant liquid was poured into a coiorimeter tube 
and the depth of color was compared with that of a standard. 
This method will be found to differ considerably from that of Schreiner, 
Sullivan, and Reid (1910). The oxidation in the soils reported was so 
great that it was found necessary to use the method already described. 
The difference between the two methods is indicated by the following: 
Schreiner, 
Sullivan, Deatrick 
and Reid 
‘TUTTE CH TE bore.6 Gk! Sees ST eu ee cn Oe AeA ee 2 to 3 hours 5 minutes 
Concentration of alo solution.........:....:.:-....- 0.125 per cent 1.0 per cent 
Hfocculatimewa emt we ec. co as ie ee ee bose eves Sheu C.H;OH HCL 
The standard used in the writer’s experiments was a solution of aloin 
which had been completely oxidized with either manganese dioxide or 
nitric acid. The results were calculated on the basis of the oxidation in 
the untreated soil as 100. 
The oxidation of phenolphthalin (made by reducing phenolphthalein 
with zine dust and sodium hydroxide) was also used as a means of testing 
the oxidation in soils. The data are given in table 11. These figures 
indicate definitely that the addition of manganese salts to soils increases 
the power to oxidize organic matter such as aloin and phenolphthalin. 
It appears that the salts which are the most effective are the perman- 
ganate, the chloride, and the sulfate. 
While the treatment with manganese dioxide seems to have interfered 
slightly with oxidation, it has been observed that soils treated with pre- 
cipitated manganese oxides, instead of the pulverized pyrolusite, oxidize 
aloin readily. The oxidation in the air-dry soil from the field was very 
weak. The increase due to the moisture treatment alone is very noticeable. 
Since the soil contains no manganese, this is due to some other cause. 
