(1) A revision of the method by Malan and Van der Lingen for the colorimetric determination of sodium in vegetation is described in detail. (2) Evidence is presented to show that:- (a) .04-0.1 mgm. Na can be determined with reasonable accuracy in the presence of 0.1 mgm. P; when 0.1- 0.2 mgm. Na is to be determined 0.2 mgm. P, and when 0.2-0.8 mgm . Na, up to 0.4 mgm. P may be present. (b) The interference of K is dependent upon absolute concentration and temperature; working at ordinary laboratory temperature ( ± 25° C.) not more than 0.8 mgm. K should be present in the aliquot for a determination. (c) At 26° C. precipitation is complete within experimental error in 30 minutes.
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