809
V O L U M E 27, N O . 5, M A Y 1 9 5 5 cross section, the perimeter of cross section, and the length. The cross-section perimeters and areas were measured with a map measure and a planimeter, respectively. The remaining measurements were made microscopically, the length being measured on unimbedded nitrogusnidine crystals, such as are shown in Figure 2, and the projected diameter being measured on the transveme sections of the strands. Frequency-distribution curves of the dat,a were made, and from these curve8 the shape factors, a and 0,were obtained by comparing the perimeter and square mot of the area, respectively, with the projected diameters. The ratio of crystal length to diameter wa8 similarly obtained.
ate between the microscopic and air-permeability values. The microscopic value is probably on the low side of the true value, as fissures and minor surface irregularities cannot he taken into account in making direct measurements. Furthermore, an accuracy within *IO% is not claimed for the Fisher subsieve siser and the value actually obtained with this instrument could he as much 8s 10% lower than that noted ahove. These consid-
RESULTS
Frequency distributions of the data. on the nitroguanidine crystals are shown in Figure 3. The values on the abscissa of Figure 3 represent (in per cent) the numher of particles less in diameter, square root of area, length, or cross-section perimeter than the corresponding measurement in microns on the ordinates. These graphs give the following values far the constants: u =
3.41
0 = 0.i3 c
=
20.8
Figure 3. Frequency distribution of crystal lengths, cross-section perimeters, cross-section diameters, and
the two types of instruments. All the measurements, therefore, may be considered as within a practical range of the true value, and the air-permeability equipment may he used for the routine determination of the specific surface of nitroguanidine within the range of 7000 to 9000 sq. cm. per cc. ACKNOWLEDGMENl
Figure 2. Photomicrograph of nitroguanidine crystals showing relative dimension of longest axis (length of orj-stal) 22ox
Instrument
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The above values for the constants and the data from the cro86section-diameter distribution shorn in Figure 3 were substituted in Equation 1 t o obtain a value for the specific surface. The average specific surface as determined with the three instruments and the per cent deviation from the microscopic value me a8 follows: MiorOsW'e. Fisher subsieve size1 Draft equioment Average of Fisher subsieve sizer and draft equipment
The authors wish to acknowledge the assistance of C. N. Bernstein, Leon Whitman, and Bryan Hancock, who furnished
Speoifie Surface. Sq. Cm./Ce. 6702
LITERATURE CITED
(1)
Drinker. P., 81id Hatoh, T., "Industrial Dust." McGmw-Hill. New York,
1 nlC IIYY.
(2) Joint Army-Navy Specification, "Nitroguanidine (Picrite)," JAN-N-494 (Sept. 10.1947). RECEWED
ior review Ootober 25. 1954
Aocepted January 21, 1855.
% Deviation from
M ~ O I O S DValue OP~
...
8460
8910
26.2 32.9
8685
29.6
The values obtained with the Fisher subsieve sker and the draft equipment are in reasonshly close agreement, aa would he expected, inasmuch as they both depend on the air-permeability principle, hut the respective values far the two air-permeability instruments do not indicate such close agreement with the value obtained microscopicdly. However, the apparent difference in the values obtained with the two types of instruments (microeeopic and air-permeability) is not as great as the results might indicate. The true specific-surface value is prohahly intermedi-
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Determined by Light Scattering-Correction
I In. the ~ ~article ~ "Method for Evaluating the Reliability of RouIr.,
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trmgelo, S.V. R., Clay, Barhara, Fishman, M. M., Hagan, A. G., Lazrus, Allan, and Zagar, Walter, BNAL.CHEM.,27, 262 (1955)l the expression in Equation 1and the paragraph ahove Equation 1 should read: H'/r, Equations 9 and 10 should read 0/2, not P. On page 264, second column, below- Table 11, the expression in line 3 should read: M,e0.'5Ba.
