excellent agreement between the trvo sets of data, the mean for the collaborating laboratories being 1.5070 potassium and the mean error for the suspension method +0.02y0potassium. The results of the collaborating laboratories are further divided into groups according to the type of analytical method; seven used chemical methods, eight used flame methoc.8, and two used spectrographic method,j. Statistical tests of the differences between means of the three groups and the new method were made by the anal: The F value obtained w%s0.32, showing t h a t the means n-ere not different according t o t h e test ( F required at P = 0.05 is 3.86, standard error of the mean 0.03s). Set 2 was a group of nine samples from a collaborative study of analytical methods reported by Ward and Heeney (3). This set included strawberry, raspberry, peach, apple, tomato, and corn leayes, grape petioles, brome grass plants, and oat grain. Results for individual samples )?-ere not given by Ward and Heeney. However, the mean value of all samples frclm the nine collaborators was reported as 1.7500 iiotassium. T h e mean error of the results found in this work by direct flamle photometry of a suspension (Tahe 11) was only -0.01% pota,,'w u m . Statistical mea.;ures of the precision of t h e new method were made. The
Table II.
Per Cent Potassium in Nine Samples from a Collaborative Study as Determined b y Flame Photometry o f a Suspension"
Set 2 Sample 1
2-
3
-1
2.08 0.60 2.93 2.11 2.09 2.93 2.15 0.61 Duplicate determinations.
~~~~
5 1.76
1.77
standard deviation of a n analysis was *0.0086 for Set 1 a n d *0.0108 for Set 2. The related relative standard deviations were O.57y0 and 0.69%. DISCUSSION
Direct flame photometry of a suspension is a useful procedure for determining the potassium content of plant material. This is believed to be t h e first application of Gilbert's suggestion of its use for quantitative analysis of powdered materials with little or no preparation. The method is very rapid, since it eliminates t h e usual ashing and dissolving of the ash required when determinations are made on solutions. It produces potassium values similar to those found b y conventional procedures. The precision of t h e analyses is very high. The mrthod should be adalitable t o
6
7
8
1.52 1.52
2.3;1 2.32
0.31)
0.39
9 1.95 1.9-1
a n y flame photometer, provided thc atomizer and burner will pa
