V O L U M E 28, NO. 9, S E P T E M B E R 1 9 5 6 in chlorine content of about O.lyO.This means that the relative accuracy of this method is better than O.lx,a substantial improvement over the Carius method. It may be possible to improve the sensitivity of the method still further by decreasing the steepness of the gradients, but this was unnecessary for the authors’ purposes and, therefore, was not investigated. This method has been applied for several years in this laboratory. hlodified according to the exigencies of the case, it may be equally valuable for the investigation of other polymers.
1457 (2) Brakke, 11.K., J . Am. Chem. SOC.73, 1847 (1981). (3) Gordon, Zf., I n d . Eng. Chem. 43, 386 (1951). Trans. Faraday Soc. 49, 31 (1953). (4) Gordon, hl.,Macnah. I. -4., (5) Kahler. H., Lloyd, B. J., Jr., Science 114, 34 (1951). (6) Linderstrbm-Lang, K.. .Vature 139, 713 (1937). (7) Linderstr@m-Lang, K., Lans, H., Jr., MLkroche’m. Acta 3, 210
(1938).
(8) Low, B. IT., Richards, F. A I . , J . Am. Chem. Soc. 74, 1660 (1952). (9) Salomon. G., Amerongen, G. J. van, T’eersen, G. J. van. Schuur, G.. Decker. H. C. J. de, I n d . Eng. Chem. 43, 315 (1951). (10) Schuur, G. (to Rubber-Stichting), Brit. Patent 726,142 (;\larch
LITERATURE CITED
1955). (11) Schuur. G., “Some Aspects of the Crystallization of High Polymers,” Ruhher-Stichting, Comm. KO, 276, p. 71, Delft, Holland, 1955. (12) Tessler, I., Woodberry, K.T., ZIark, H., J . Polymer Sci. 1, 437 (1946). (13) T’eersen, G. J . \.an, Proc. Rubber Technol. Conf., 9nd C o n i , , p . 87. London, 1948.
(1) Boyer. R . F.. Spencer, R. S., Wiley, R. 11..J . Polymer Sci. 1,
RECEIVED for review October 28, 1955. Accepted May 5 , 1936. Com-
ACI99% silicon was used in preparation of some of the samples. Weighed amounts of the metal were mixed with an amount of neutron inert material (CaO) to give a constant final volume of sample. Although the neutron activation of calcium is low, its presence interfered with the analysis of samples of very low silicon content. Aluminum oxide (Baker’s c.P.)was used in the reparation of aluminum reference samples. I n the case of the aLminum samples, potassium dichromate was used as the diluting agent to maintain a constant volume of sample. Two samples, sand and quartz, were analyzed in these laboratories for silicon and aluminum content by ordinary wet chemical methods. RESULTS
Silicon. Silicon, bombarded with 14-m.e.v. neutrons, yields the 2.4-minute half-life aluminum-28 activity (7) with a gammadecay energy of 1.78 m.e.v. Silicon concentrations were determined with the discriminator set to accept only those pulses due to gamma rays of energy greater than 1 m.e.v., in order to bias out the effect of the magnesium activity produced from the aluminum in the sample. Bombardment times of approximately 30 seconds a t a target current of about 30 pa. were used. .4s the neutron source was almost a point source, it was necessary to maintain a constant volume of sample in the plastic vial in order to hold the bombardment geometry constant. A monitor sample
All08
0.250 0.125
Specific Activity, Counts/Min./G. AlzOa Av. 45,400 46,000 46,400 45,900 44,500 42,700 42,400 43,200 48,200 49.400 48,000 48,500 44,100 44,100 45,280 44,500 46,000 44,000 44,450 43,600 44,450 47,500 45,900 45,300 47,500 46,500 Av. 45,500 f 1700 or 3.8% 50,500 50,500 49,000 49,200 49,800 50,800 54,200 52,250 52,400
The results of 14 repeat runs on the same sample (quartz, 2.72 grams) yielded 185,500 + 2200 counts, or an observed standard deviation of 1.2% with a maximum deviation from average of 2.2%. Aluminum. Bombardment of aluminum by 14-m.e.v. neutrons yields two activities ( 7 ) . Magnesium-27, produced by the n - p reaction on aluminum-27, has a half life of 9.6 minutes and gamma-decay energies of 0.84 and 1.01 m.e.v. Sodium-24, produced by the n - 01 reaction, has a half life of 14.7 hours and gamma-decay energies of 1.38 and 2.75 m.e.v. Aluminum was determined by using the 14.7-hour sodium-24 activity and counting on the integral bias plateau of the crystal counter a t a fixed discriminator setting. I n order to enhance the effect of the 14.7hour activity, the samples were bombarded for 1.5 hours a t a neutron flux of the order of 5 X lo7n. sq. cm./second. -4rotating sample holder, with 10 samples mounted around the periphery, was used to enable a number of samples to be bombarded simultaneously and to distribute the flux equally among all the samples.
V O L U M E 2 8 , N O , 9, S E P T E M B E R 1 9 5 6 As in the silicon determinations, a constant volume of sample was used in order to maintain a constant bombardment geometry. I n each case, a flux monitor sample (1.00 gram of aluminum oxide) n-as included among the samples during bombardment. At least a 2-hour delay after the end of bombardment was required to allow for the decay of extraneous activities, such as that due to aluminum-28 (2.4 minutes) and to magnesium-27 (9.6 minutes). Under these conditions, the principal interfering elements are magnesium and iron. The observed relative specific activities produced by these elements are 1.37 for niagriesiuni (as RlgO), 1.00 for aluminum (as AlZOa), and 0,575 for iron (as Fe203). Although this paper is concerned with aluminum analysis, the method should be equally valid for any one of the three elements in the absence of the other t1v-o. -3.11 samples nere counted for 10 minutes and corrected for decay to the time of the start’ of the first sample count. The resulting value, when compared with the monitor count, n-as proportional to the aluminum content. The results of 27 analyses of eight samples containing aluniinum ranging from 0.125 to 2.00 grams (as aluminum oside) are shon-n in Table 111. The observed standard deviation of the values for the first six samples is 3.87,, with a maximum deviation from average of 7.6%. These errors are some\yhat larger than nould be snticipated and could conceivably be attributed to unequal neutron flux variations on the sample and the monitor, or to some unrecognized source of error. T h e last two samples of low alumina content shov appreciably higher values for counts per gram prcsunisbly due t o scattering or self-absorption effects. For t h t w low concentrations, it may be possible to establish a ca1ibr:itioii curve for the specific activity. The results of 10 ana1ysr.s of a single concentration of nluminum oside (1.00 gram) yielded 45,500 i 790 counts or an oh-
1459
served standard deviation of 1.8% with a maximum deviation from average af 2.8%. CONCLUSIONS
1 rapid method for the quantitative estimation of silicon and aluminum has been established. Although its accuracy is less than conventional wet chemical means, the considerable saving in time and effort justifies its use. At present the method is accurate to within 5% for samples containing 0.40 gram or more of silicon dioxide and a0.50 gram or more of aluminum oxide, n.ith the flux of fast neutrons readily available from a low energy positive ion accelerator. With a suitable calibration curve the range of concentrations for useful application of the method may be extended. ACKNOW LEDGBl ENT
The author Tvishes to express his appreciation to R. L. Caldwell and Sorman Hackerman for helpful discussion of the problem: to James Q. Wellborn for obtaining some of the data contained herein; and to the management of the RIagnolia Petroleum Co. for permission to submit the paper for publication. LITERATURE CITED
(1) Boyd. G. E.. ATAL. CHERI. 21. 335 (1949). ~~, ( 2 ) Brooisbank,’ W. $., Leddicotte, G: IT.,’lIahlman, H. .4.,J . P h y s . Chem. 57,815 (1953). I
(3) Leddicotte, G. W., AIahlman, H. A., .-lsa~.CHEM.27, 823-5 (1955). (1) Leddicotte, G . W., Reynolds, S. A, Sucleonics 8, S o . 3, 62 (1951). ( 5 ) IIeinke, W. TI‘., Science 121, 177-84 (1955). (6) lluehlhause, C. O., Thomas, G. E., .VucZeonics 7, So. 1, 9 (1950). (7) Satl. Bur. Standards, “Suclear Data,” Circ. 499 (1950). ( 8 ) Paul, E. B., Clarke, R L., Can. J . Phys. 31, 267 (1953) RECEIVED f o r r e i i e w J a n u a r y 21, 1956. Accepted AIay 31, 1938.
Rapid Analytical Electrophoresis Employing Prismatic Cell GERSON KEGELES Department
OF
Chemistry, Clark University, W o r c e s t e r 7 0,
A n optical arrangement for moving-boundary electrophoresis is described, which uses a cell of prismatic cmss section and directly plots the refractive index gradient Z’S. the refractive index increment. Experimental results and diagrams for serum analyses, as well as the analysis of optical sensitivity and systematic errors, indicate that this arrangement is at least equal in accuracy to schlieren optical methods. The arrangement permits rapid analytical electrophoresis work of high accuracy, because resolved components are recognized as separate peaks just as with schlieren optical arrangements, while relative concentrations are read directly as lengths with a reticle eyepiece.
Mass.
jection optical system using a point source of light and a prismatic cell to plot directly the refractive index against the gradient of refractive index (6). I n the diagrams obtained, visual resolution of partially separated boundaries is as satisfactory as that obtained n ith schlieren refractive index gradient recording techniques (10, 11, 16). However, diagrams from this prismatic arrangement also contain the relative refractive index increments in the form of distances between successive gradient dips in the diagram. Consequently, concentration measurement proceeds very rapidly, and can be made with a precision intermediate between that of schlieren and interferometric (1, 3, 8,9, 12, 1 4 ) methods. KO cell position coordinates are defined in these diagrams, and mobilities are obtained, \\-hen required, with auxiliary optical devices. OPTICAL ARRANGEMENT
P
RISLIATIC arrangements have been employed for the study of inhomogeneous liquid columns occurring in sedimentation equilibrium ( b ) and electrophoresis (8, 18). These arrangements have the advantage of depicting the distribution of iefractive index (or concentration) directly. TJ7ithout some arrangement for also recording refractive index gradient (5, 18), however, a prismatic system does not offer satisfactory visual resolution of partially separated moving boundaries, the refractive index gradient function being superior in this respect (13). T h e present arrangement takes advantage of a very simple pro-
The schematic arrangement of the optics is shown in Figure 1. Light from the point source, P , is received by the astronomical telescope achromatic objective, L , placed a t its focal length, F , away from the source. Parallel light is projected into the electrophoresis cell, C, whose rear window is externally silvered to return the light through lens L. Source P is slightly off the axis of lens L, so t h a t the returning light beam impinges on mirror N and comes to focus, in the presence of uniform liquid throughout the cell, C, and its surrounding mater bath, as a sharp image of the point source on the screen, S. Figure 2 shows a schematic arrangement of the top view of one column of the cell, which aids in following the lateral light deflec-
