The 0.95, 90% tolerance intervals (2) indicate the degree of reproducibility available by the amperometric method. From the data for Laboratory h we can predict with 0.95 confidence that at least 90% of all determinations run on a similar material would lie in the interval fif f 0.037y0vanadium, where M indicates the average of a large number of such determinations. I n other words, a t least 90% of all determinations which may be run on a single sample would be within a range of 0.074y0 vanadium. A similar range calculated from column 2 is 0.150y0 vanadium, while for the visual method it would be 0.380% vanadium. It is apparent t h a t precision can be maintained which is equal to classical weight-buret titrimetry, since a salt reductant, with a favorable molar equivalent ratio, is weighed. The backtitration using amperometry is a very exact means of end point detection. A summation of the complete analysis of the vanadium metal standard is included in Table 11. These data are reported for reference as to the probable content of minor impurities. Accountability of components appears to be very nearly complete (99.987%). ACKNOWLEDGMENT
The author thanks I. H. S. Fraser, A. R. Gahler, F. N. Hopper, C. XI.
Table
II.
Analysis of Vanadium Metal Standard
Found, % 99.727
Element Vanadium
0.065
Oxygen Hydrogen Nitrogen Carbon Iron Silicon Calcium Magnesium Chromium Aluminum Manganese Molybdenum Titanium Lead Cobalt Nickel
No. of detns. 12
0.004
2 2 2 3
0.036
Single
0,030 0.052 0.032 0,020 0.007 0.007 0.007
