JANUARY 15, 1940
ANALYTICAL EDITION
to 20 ml. The hydrochloric acid wash is added in small portions, each being allowed to drain down to the top of the column before the next is added. The first two or three portions are used to rinse the beaker that had contained the iron solution.
Indicator Correction with PhenanthrolineFerrous Ion For titrations with ceric sulfate conducted in a volume of about 250 ml., one drop of 0.025 M o-phenanthroline-ferrous indicator solution is satisfactory. Walden, Hammett, and Edmonds (3) showed t h a t for titrations with 0.01 M ceric sulfate of small quantities of iron requiring a titer of about 10 ml., the indicator correction is very small (less than 1 per cent of the titer) and reproducible. Fryling and Tooley (1) used about the same amount of indicator, but since the correction represented as much as 5 per cent of the final titer they advised the careful pipetting of a correspondingly larger volume of a more dilute indicator solution t h a t had been standardized against ceric sulfate. There appears to be no particular advantage in the use of so large a n amount of indicator in the microdetermination, since the most striking color change takes place after the greater part of the indicator has been oxidized. Thus the authors have found that the amount of indicator can be reduced to 2 drops of 0.001 Aif solution. The indicator correction is then only 0.010 ml. of 0.01 M ceric sulfate as determined by direct titration in 30 ml. of 1 M hydrochloric acid to the disappearance of the indicator color.
Reductor Blank When 30 ml. of 1 M hydrochloric acid are passed through the reductor, the solution is treated with 2 drops of 0.001 M o-phenanthroline-ferrous indicator, and the mixture is titrated to the disappearance of the indicator color, 0.016 9: 0.001 ml. of 0.01 M ceric sulfate is required. Allowing 0.010 ml. as the volume of oxidant required to bleach the indicator, the remaining 0.006 ml. is probably consumed by a trace of peroxide formed in the reductor. T h e situation is different, however, when the solution passing through the reductor con-
61
TABLE I. TESTAX~LYSES Fe Taken
Ce(SO4):
Fe Found
Mg.
M1.
Me.
Error in F e MQ.
0.686 0.686 0.686 0.686 1.372 1.372 1.372 1.372 1.372 2.068 2.0% 2.038 2.058 2.744 2.744 2,744 2.744
1.127 1.133 1.122 1.135 2.254 2,253 2.249 2.246 2.249 3.380 3.383 3,381 3.386 4.497 4.505 4.502 4.508
0.687 0.690 0,684 0.692 1.374 1.373 1.371 1.369 1.371 2.060 2.062 2.061 2.064 2.741 2.746 2.744 2.746
f0.001 + O , 004 -0,002 4-0.006 +o. 002 +0.001 -0.001 -0.003 -0,001
+o,
002
+0.004 +0.003 +0.006 -0.003 +o. 002 0.000 +0.002
tains iron, for then some iron reoxidized by a trace of peroxide would probably be reduced before it leaves the reductor. Thus the error would certainly be less than that represented by the total reductor blank of 0.006 ml. which would be equivalent to a negative error of 0.003 mg. of iron. Table I shows, moreover, that no correction is needed beyond that for the indicator blank.
Method of Analysis Ten milliliters of 1 M hydrochloric acid solution containing the
iron as ferric alum mere poured through the reductor at a rate of 10 ml. per minute, and the column was rinsed with 20 ml. of 1 h‘ hydrochloric acid. Two drops of 0.001 M o-phenanthrolineferrous indicator were added and the mixture was titrated with 0.010916 M ceric sulfate using a calibrated 5-ml. microburet. The results of the test analyses arc given in Table I. The indicator correction of 0.010 ml. has been subtracted in each case.
Literature Cited (1) Fryling and Tooley, J. Am. Chem. Soc., 58, 826 (1936). (2) Walden, Hammett, a n d Chapman, Ibl’d., 55, 2649 (1933). (3) Walden, Hammett, a n d Edmonds, Ibzd., 56, 350 (1934).
Preparation of Microscopic Glass Spheres C. R. BLOOJIQUIST ~ N -4. D CLARK, Battelle Memorial Institute, Columbus, Ohio
D
U R I N G work on a study of the solid-liquid interface i t became desirable to prepare a relatively large quantity of microscopic particles of known surface area. The use of glass spheres was suggested by Bishop ( I ) , who mentioned the fact that perfect glass spheres may be prepared b y passing powdered glass through the flame of a blast lamp, but did not give details of the process. Recently, Sollner (3) described a method of preparing the spheres in a similar manner and collecting them by directing the flame against a water surface so that the fused particles are thrown into the water. H e stated that i t was impossible to prepare spheres of Pyrex glass in this manner without the use of a n oxy-hydrogen flame. The method used in this work is basically the same as that described by Sollner, but instead of collecting the fused particles in water, the authors have found i t more convenient to cool the gases and glass particles from the flame b y passing them through a short length of pipe and then drawing them by suction into the bag of a n ordinary household vacuum cleaner. In this way i t is possible to prepare spheres u p t o
25 microns in diameter from ordinary Pyrex glass b y using a laboratory blast lamp with natural or city gas and compressed air.
The glass powder is prepared by wet-grinding Pyrex tubing in
a ball mill with steel balls. After several hours’ grinding the suspension is poured into a 2-liter beaker and stirred thoroughly; the particles which have not settled in 5 minutes are decanted and allowed t o settle completely. These particles are treated with chromic acid cleaning solution t o remove impurities, washed free of sulfate ion, and dried thoroughly. The apparatus used in preparing the spheres is shown in Figure 1. Theglass powder, which has been thoroughly dried at 110’ C., is placed in a wide-mouthed bottle of approximately 200-cc. capacity. The gas is ignited and the compressed air turned on gradually until a flame of the proper size is obtained. A large “brush” flame extending about one half the length of the stove pipe works well. The stove pipe is 63.5 cm. (25 inches) long and 12.5 cm. ( 5 inches) in diameter. As soon as the flame is burning evenly and steadily, the vacuum cleaner motor is turned on and allowed to run until sufficient particles are collected or the vacuum-cleaner bag becomes too hot. A 20-cm. (8-inch) glass funnel attached t o the suction end of the vacuum cleaner and
GLASS POWDER
~
particles in the SO-minute fraction is shown in Figure 2. The mean diameters of the
