Vol. 4. No. 3
ANALYTICAL EDITION
340
time when the dryer failed, as determined by experimentation, was reduced by 4 minutes, thus giving the actual life of the drying agent. All drying agents tested were dehydrated at 400" C. under a total pressure of 20 mm. of mercury, with the exception of aluminum oxide and magnesium perchlorate. Aluminum oxide was dehydrated by heating to 1000" C. for 6 hours, magnesium perchlorate by gradually heating to 200" C. under a total pressure of 5 mm. of mercury. TABLEI. CAPACITY OF DRYING AQENTS WT.OF WT. OF MATEW A T ~ R RIAL OCCUPY- WATER ABSORBED ING 15 cc. ABSORBED Minutes Grams Gams % 71 3.04 11.2 27.2 ALOE 56 2.40 7.5 32.0 Mg C10d1 56 2.40 11.0 21.8 ca&a 25 1.11 30.0 3.7 BaO CaCh,sodalime (50% each) 20 0.86 9.5 9.05 I6 0.69 27.0 2.6 BaOi Ala SO4)a 13 0.56 7.4 7.6 6 0.258 15.2 1.7 NabH pellets 4 0.172 11.6 1.5 NazSOi 2 0.086 7.8 1.1 MgCla 1 0.043 8 . 3 0.52 MgSOr crto 1 0.043 21.2 0.21 DRYING AGENT
LIFE
COMPARATIVE CAPACITIES OF VARIOUS DRYINGAGENTS Of the twelve drying agents tested in the above manner, only three were able to protect the catalyst for a minimum of 1hour. Some of the drying agents permitted a small amount
of water vapor to escape from the start, the amount increasing as the material became hydrated. Calcium chloride, calcium oxide, and sodium hydroxide belong to this class. Others completely absorbed the water vapor up to a certain point, and then broke sharply, causing a rapid decrease in the activity of the catalyst. Magnesium perchlorate, aluminum oxide, sodium sulfate, barium oxide, and barium peroxide belong to this group. Table I contains the experimental data, 15 cc. of drying agent and 20 cc. of catalyst being used in each test. The significant value in this table is the weight of water absorbed by a definite volume of drying agent. Aluminum oxide absorbed the most water; next were calcium chloride and magnesium perchlorate. The others had relatively poor capacity. It is of interest to observe that calcium chloride and magnesium perchlorate have the same capacity for water, although calcium chloride has a higher vapor pressure than magnesium perchlorate. The important difference in their behavior is that calcium chloride permits a small but measurable amount of water vapor to escape from the start, whereas magnesium perchlorate completely dries the gas until its capacity is reached. R ~ C E I V EMarch D 4, 1932. Presented before the Division of Gsa and Fue Chemistry at the 83rd Meeting of the American Chemical Society, New Orleans, L a , March 28 to April 1, 1932. Contribution 229 from the Department of Chemistry, University of Pittsburgh.
Direct Gravimetric Determination of Sodium in Commercial Aluminum EARLER. CALEY,Frick Chemical Laboratory, Princeton University, Princeton, N. J. HE magnesium uranyl acetate method for sodium is
T
capable of giving satisfactory quantitative results when minute quantities of the element are present ( I ) , and aluminum does not interfere with the determination (3). Since sodium is sometimes present as an impurity in aluminum, it was thought desirable to ascertain whether or not this method could be applied directly for estimating the percentage of this impurity in the commercial metal, and thus avoid difficulties inherent in any method based upon the preliminary separation of the sodium from the aluminum and other components of this material. The samples for the experiments were furnished through the courtesy of the Research Laboratories of the Aluminum Company of America. As the result of certain preliminary trials, the procedure followed was first to dissolve the weighed sample of drillings in the minimum possible amount of dilute hydrochloric acid, using a silica dish for this purpose. After dilution with water, the solution was filtered and the filtrate was concentrated to the smallest possible volume in a Pyrex flask, usually until hydrated aluminum chloride just started to separate. Then 100 cc. of magnesium uranyl acetate reagent were added and the determination completed as detailed elsewhere (2, 3). Apparently the various other impurities in the particular samples examined caused no interference. Precipitates were examined for silica with a view to applying a correction, but the amount present was always found to be insignificant. There was no reason to suspect that metallic impurities would cause error, and no evidence was found that they did. With a sample of comparatively high sodium content the method proved quite satisfactory, As the results in Table I
show, the individual determinations checked well with each other and with the value for the sodium content of this particular material as determined in the laboratories of the Aluminum Company of America by their procedures. With a sample of somewhat lower sodium content, however, considerable difficulty was experienced in reducing the solution volume of the necessarily larger sample down to the point required for obtaining correct values by this method. The irregular results obtained in the second group of determinations reflect this difficulty. Even the use of a more concentrated reagent and the addition of this to larger volumes of solution, in this case 10 to 12 cc., as recommended in a recent paper ( I ) , failed to produce entirely acceptable results. The last three vaIues in the table were obtained in this manner.
DETERMINATION OF SODIUM IN COMMERCIAL TABLEI. DIRECT ALUMINUM WT.OF SAYPL~ SAMPLE TAKEN Urams A 0.750 1.000 1.500
B
B
2.000 2.000 2.000 2,000 2.000 2.000 2.000 2.000
2.000
WT.OF SODIUM FOUND PPT. To3rd To,2nd FOUND decimal decimal Gram % % 0.04 0.0183 . 0.037 0.035 0.04 0.0230 0.037 0.04 0.0357 Av. 0.036 0.04 0.0114 0.009 0.01 0.016 0.02 0.0204 0.013 0.01 0.0171 0.014 0.01 0,0185 0.007 0.01 0,0095 0.015 0.02 0,0190 Av. 0.012 0.01 0.009 0.01 0.0115 0.008 0.01 0.0107 0.013 0.01 0.0173 Av. 0.010 0.01
STATED VALU~
% 0.04
0.009
0.000
July 15, 1932
1.NDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
In general, it was apparent from the experiments that the amount of sodium in sample B represented the lowest possible percentage that could be estimated by this procedure, and that even in this case the results were not very satisfactory. It is recommended, therefore] that this method be applied only to the determination of sodium in metallic aluminum when the percentage of this impurity is greater than 0.01 per cent.
34 1
When this is the case, the above simple procedure is capable of yielding good results.
LITERATURE CITED (1) Caley J Am Chem. Soc., 54,432-37 (1932). (2) Caley’a;d Fo;lk, IMd., 51, 1664-,4 (1929). (3) Caley and Sickman, Ibid., 52,4247-51 (1930). February ST, 1932.
Construction of Accurate Air Separator PAULS. ROLLER, U. S. Bureau of Mines, New Brunswick, N. J. HE author has previously described (1) a new type o€ air separator holding a charge of 600 cc. of powder and capable of effecting a particle-size separation into successive fractions beginning with 0-3 or 0-5 microns. Operations with this apparatus were a t the time confined chiefly to Portland cement and pulverized anhydrite. Recently there has been occasion to fractionate a gypsum powder that had been ground very fine in a pebble mill. I n making a 0-5 micron cut on this material the rate of separation was found to be unusually low compared to the corresponding anhydrite fraction, even when allowing for the smaller rate of air flow due to the lower density of gypsum (2.32 as against 2.98). With the anhydrite the rate a t which 0-5 micron particles collected in the felt filter bag, averaged over the first hour and a half, was 27 grams per hour; with the gypsum, however, the rate was only 3.3 grams per hour. The difference was attributed to suspension and adherence of the soft fine gypsum particles in the lower conical portion of the 60.8-cm. (24-inch) settling chamber used. To counteract this condition, it was decided to tap the conical portion automatically. When this was done the 0-5 micron gypsum fraction separated out much more rapidly; the rate, averaged over the first hour and a half, being 16 grams per hour as against 3.3 grams per hour without t a p p i n e i . e., the increase in rate was fivefold. Besides greatly augmenting the rate of separation, the automatic tapper also increases the homogeneity of a given fraction. To understand how this comes about, it is recalled that in a given fractionation the particles that are blown over progressively increase in size with time. At the end point, corresponding to a definite rate of separation, which depends upon air flow and particle size and may be as ligh as 10 or 12 grams per hour, the particle sizes are in the boundary between the given fraction and the next succeeding fraction. If the fractionation is prolonged beyond the end point, the particle sizes will increase to a maximum value 1.41 times the theoretical maximum given by Stokes’ law. This is because the maximum velocity a t the center of the vertical chamber is by Poiseuille’s law twice the mean velocity. Automatic tapping of the settling chamber renders the succession of particle sizes blown over more uniform, so that at the end point the number of particles which are greater or smaller than the theoretical maximum in size are reduced to a minimum. This result is particularly important at the higher rates of air flow. Because of the pronounced increase in rate of separation and greater homogeneity of the fractions, not only for gypsum but also as observed for all other powders, the automatic tapper is now used as a standard adjunct to the air separator previously described (1). The construction and method of mounting the automatic tapper, I, are shown in Figure 1. The oscillations of the U-tube, C, about bearing B impart the required motion to the tapper. The latter consists of three leaves, clipped to-
gether, of 0.8-mm. (l/az-inch) spring steel about 4.5 cm. (1.75 inches) wide and 30.5 cm. (12 inches) high, At the upper end is a wooden hammer head weighted with lead so as to give an optimum blow. At the lower end the tapper is clamped in cantilever fashion to an L-shaped bracket which moves along a slotted horizontal plate. The latter is rigidly attached to the U-bend by means of uprights. The
FIGURE 1. AIR SEPARATOR,VERTICALSECTION tapper is brought into position for maximum impact by moving it along the two slots in the horizontal plate, and is fastened in place on the horizontal plate by means of washers and wing nuts that screw onto bracket studs projecting through the slots.
LITERATURE CITED (1) Roller, IND.ENG.CHEM.,Anal. Ed., 3, 212 (1931). RXICEIVED February 23, 1932. Published by permission of the Director, U. 9. Bureau of Mines. (Not subject t o copyright.)
