478
INDUSTRIAL AND ENGINEERING CHEMISTRY
was extended to determine the velocity of particle fall, by means of Equation 4, i t was necessary to assume that all the particles fell with the same velocity and that this velocity was constant with time. I n other words, Stokes’ law was assumed to hold and the particles were assumed to have the same diameter. For those cases where the particles do not fall with uniform velocity, the theory given above must be modified. However, since the method gives a n almost instantaneous value for velocity, i t can be used to determine just when the mixture failed to,settle according to St,okes’ law. This suggests that the method could be applied successfully to a study of the interval between the time that settling begins and the time at which “conglomeration” or interference occurs. I n this experiment no special precautions were taken to ensure uniformity of particle size, and consequently there seemed to be no justification for using Stokes’ law to calculate particle diameter. It was known that the sizes varied from 1to 74 microns, but only the 325-mesh screen was available between these sizes. If size distribution could have been determined, i t would have been possible to relate this method to other methods of sedimentation. Probably this could best be done by the use of a n effective size or uniformity
Vol. 13, No. 7
coefficient in place of an average diameter. These terms a r e used in the analysis of filter sands. If settling is in the viscous range, interference would presumably be negligible even at high coal concentrations. Stokes’ law could then be written as KD2p’ - KD2p
v=
P
where K is a constant, D is the effective size, p’ is the density of the coal, p is the apparent density of the liquid, and p is the apparent viscosity. Both p and p would vary as settling progressed, but for any given system the relation between them could be expressed a t least graphically. Since it would be extremely difficult to determine the rate of settling of coal particles in oil by any other method, the samples could not be checked. However, the pendulum method as a method could be tested, using lead shot falling through a transparent liquid and observing the rate of fall visually. A study of settling theory by means of the pendulum is contemplated using these materials.
Literature Cited (1) Manning, A. B., and Taylor, R. A. A., Trans. Inst. Chem. Engrs. (London), 14,45 (1936).
Preparing Gas Distributors Using Alundum Disks S. EDWARD JOLLY Experimental Division, Sun Oil Company, Norwood, Penna.
A
NUMBER of methods have been described in the literature for the preparation of sintered- or fritted-glass filters from Pyrex glass (1-8). These filters are very satisfactory and are especially valuable for use as gas distributors in systems where intimate contact between a gas and a liquid is desired. These methods require considerable time to prepare the glass, and the equipment needed is not always available in chemical laboratories.
During the last several years, the author has used gas distributors prepared by sealing Alundum disks to Pyrex. These distributors have been very satisfactoy. A Pyrex tube of slightly smaller diameter than the disk t o be used is flared until the dibk will fit inside the flared portion as shown in Figure 1 (top). The glass is then heated in the flame of a blast lamp and, as the glass is softened, it is worked against the disk and slightly rolled over the outside of the disk. For use as an aerator, a small connecting tube is sealed on and bent so that the gas is delivered upwards (Figure 1, left). Alundum thimbles may be used in place of disks. Filters may be prepared by constricting a Pyrex tube of suitable diameter so that the disk will be held at right angles to the axis of the tube (Figure 1, right). By heating and pulling the tube, a seal is obtained. Filters of this type are convenient for sealing into all-glass systems. This metLod requires no special equipment and may be carried out by anyone with a n elementary knowledge of glass bloa ing. Careful annealing of the Alundum-to-glass seal is not required. AundLm disks are made by the Norton Company, Worcester, Mass., and may be obtained in at least two degrees of porosity. For ordinary laboratory usage, disks 0.75 and 1 inch in diameter are most suitable.
Literature Cited FIGURE 1. SEALING ALUNDUM DISKSTO PYREX GLASS
Attempts have been described to seal Alundum disks directly to Pyrex glass ( 2 ) . While no details have been given regarding the method of preparation of these seals, the results are stated to have been unsatisfactory.
Briscoe, H. V. A., and Lowe, A. R., J . Chem. SOC.,1934,1379-80. Bruce, \A’. F., and Bent, H. E., J . Am. Chem. SOC.,53, 990-2 (1931). Cool, R. D.,and Graham, J. D., IND.ENQ. CHEM.,Anal. Ed., 6,479 (1934). Furnstal, A. H., and Johnson, B., Plant Physiol., 11, 189-94 (1936). Kirk, P.L., IND.ENG.CHEM.,Anal. Ed., 7, 135-6 (1935). Kirk, P. L., Craig, R., and Rosenfels, R. S., Ibid., 6,154-5 (1934). Mattikow, M., Ibid., 7, 136 (1935). Stone, H.Vir., and Weiss, L. G., Ibid., 11, 220 (1939).
