JUNE, 1951
299
THE USE OF UNWEIGHED IRON WIRE AS A PRIMARY STANDARD MICHAEL CEFOLA, MALCOLM J. ROGERS, and LEO K. YANOWSKI Fordham University, New York 58, New York
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use of weighed portions of iron wire as a primary standard for the standardization of potassium permanganate and other oxidizing agents may be found in practically any elementary textbook of quantitative analysis. The authors of this paper, while working with samples of iron wire, were surprised t o find that the diameter of the wire was extremely constant. This finding suggested the use of measured lengths of wire in place of weighed amounts as a primary standard. A very simple method was devised for cutting the iron wire. A Hoffmann screw clamr, was attached t o one end of a meter stick and th; wire held firmly by means of the clamp. The wire was then stretched t o the desired length and cut by scissors. The samples were then rolled in a small coil and weighed. Table 1shows the agreement in weights and analysis of different lengths of wire, 9 mils in diameter. The results of the analysis for iron content of the different samples are included in the table to show the constancy of purity of the particular spool of iron wire used for these experiments. TABLE 1 Analvsis of Measured Lengths of Cut Iron Wire
TABLE 2 Results of Weighing 75-cm. Lengths of Iron Wire Cut by Three Individuals
B Weight, . .~g.
A Weight, . . .a.
C Weight, g, ~
~~
0.2381 0.2381 0.2383 0.2380 0.2380 0.2380 0.2380 0.2382 0.2381 0.2382 0.2381 0.2383 0.2381 Average 0.2381 Average 0.2381 Average Average deviation, 0.43 part per thousand.
short lengths of wire the precision of the weighings was still within acceptable limits for many types of quantitative work. TABLE 3 Results of Weighing Six 5-cm. Lengths of 14-mils Iron Wira
Weight, g.
Weight, g.
Average deviation, 2.6 parts per thousand.
Experimental results have shown the feasibility of preparing iron standards from iron wire by cutting desired lengths after initially determining the assay or the density. If the iron wire is sufficiently pure, as shown by the manufacturer's assay, only one weighing is necessary t o establish the relation between the lengths to be cut thereafter t o obtain known standards. This has the obvious advantage of eliminating time-consuming weighings as well as titrations. Where time is a factor this method should have very practical use. Weighings and titrations could be abolished completely To show further the agreement between length and if information as t o the exact assay, density, and diamweight of the cut iron wire four dierent 75-om. lengths eter were given by the manufacturer. were cut and weighed by three persons a t different ACKNOWLEDGMENT times. The authors wish to thank the Mallinckrodt ChemiSix samples of iron wire 14 mils in diameter were also cut in 5-cm. lengths and weighed. Even with such cal Works for supplying samples of iron wire. Weight, 9. 0.1586 0.1589 0.3170 0.3172 0.2380 0.2380 0.2382 0.2379 0.2382 Averme
