Apparatus for Measurement of the Density of Porous Solids K. A. KRIEGER Department of Chemistry and Chemical Engineering, Univeraity of Pennsylvania, Philadelphia, Pa.
A
N APPARATUS for the measurement of surface area (%)
surdly high densities, and high values are in general suspect for this reason. The table below gives a few typical results, and more extensive data, to be published later, will show that a reproducibility of 1 to 2% can be expected with this apparatus, even with materials of unfavorable bulk density.
has been found convenient for the measurement of the density of porous solids with helium as the displaced fluid. Although excellent apparatus for this purpose has been described elsewhere (I, 3, 4,6),it-frequently happens that surface areas and densities are of interest to the same worker. APPARATUS AND PROCEDURE
Sample
The apparatus is identical with that shown in Figure 1 of (2) except that bulb A is replaced by a much larger bulb, A', preferably of about 75-cc. capacity, joined as shown to stopcock 1 through a ground-glass joint. Of the several procedures which could be followed in the use of this apparatus, the following has been found most satisfactory: DETERMINATION OF APPARATUS CONSTANTS.With A' empty, stopcock 1 open, and the mercury level a t a, evacuate the entire apparatus, close stopcock 1, admit helium to a pressure of 20 to 25 cm., raise the mercury to the bottom of B,, evacuate E , and measure the pressure in the system. Raise the mercury to a higher level and measure the pressure again. Calculate the volume, y, from stopcock 1 to the top of bulb BI (not including the stopcock bore) by the gas law. Knowing y, calculate the product, p V , of the pressure and volume of the admitted gas with the mercury a t 'several of the marks,. The deviations of the individual p V ' s from their average, p V , should not exceed a few tenths per cent. With the mercury near the middle mark, open stopcock 1 and determine a new set of pressures for several settings of the mercury. We now have:
-
q P4
=
-
P3'
=
+ Bs + Bz + B , + + 20 ( B , + Bz + B1 + + Y) (B,
G./cc.
Glass beads Bauxite
....
Q./cc.
2.30 2.73 2.79 2.77 2.77 2.76
* 0.02
LITERATURE CITED
(1) (2) (3) (4)
Howard and Hulett, J. Phys. Chem., 28, 1082 (1924). Krieger, IND.ENG.CHEM.,ANAL.ED.,16, 398 (1944). Schumb and Rittner, J . Am. Chem. Soc., 65, 1692 (1943). Smith and Howard, IND. ENG.CREM.,34, 438 (1942). ( 5 ) Stamm, J . Phys. Chem., 33, 398 (1929).
1
Analytical Advisory Board Meeting The Advisory Board of the ANALYTICAL EDITION, INDUSTRIAL AND ENGINEERING CHEMISTRY, met at the summer offices, Marine Biological Laboratory, Woods Hole, Mass., on Saturday, July 14. Present were R. P. Chapman, J. R. Churchill, T. R. Cunningham, M. G. Mellon, B. L. Oser, H. H. Willard, and L. T. Hallett, associate editor; B. L. Clarke, G . E. F. Lundell, and R. H. Muller were unable to attend. Considerable discussion was devoted to the character of articles that are being offered for publication in the ANALYTICAI, EDITION, and regret was expressed that present conditions have limited somewhat research in colleges and universities and that consequently there has been some falling off in receipt of papers from these sources. Statistics were presented to the board regarding the number of papers submitted for consideration, which is slightly larger than last year: the proportion of papers that are rejected for one reason or anothei continues almost unchanged from year to year. I t is proposed to publish from time to time in the ANALTYICAL EDITIONeditorials on subjects that are of particular interest to its readers. One such that will appear at an early date will have to do with the training of analysts, from the point of view of industry, perhaps followed by a complementary discussion from the academic point of view. Regret was expressed by members of the board that the quality of training of analytical chemists is deteriorating in many institutions at the present time, and that there is a regrettable lack of appreciation in industry of the importance of this type of work. In an effort to promote consistency in the use of scientific terms, both among chemists and between chemists and other groups of scientists, the ANALYTICAL EDITION is to pubIish committee reports on nomenclature, with definitions of terms in frequent use but often misused. Papers from the Regional Section Meetings and the Meeting-inPrint are being received and will be published as promptly a8 possible.
'W
x -
2.32
Thermostating the apparatus is almost a necessity for this work, and constancy to +0.lo C. is desirable. This apparatus requires rather large samples-Le., the true volume of the sample should not be less than 10 cc. for 2% reproducibility-but on the other hand the sample is not injured by the process.
nhere p4', p,' . . . . . . are the pressures with 4, 3 , . . , . , , bulbs empty, Bd, B3 . . . . . . . are the volumes of the bulbs, and x is the volume of bulb A' to and including the bore of stopcock 1. Calculate the mean value of x from Equations l. x and y are constants of the apparatus and need be determined only once. In an apparatus of the dimensions suggested, it, should be possible to determine x to about 0.1 cc. and y to a few hundredths of 1 cc. DETERMINATION OF DENSITY. Fill bulb A' nearly to the top with a weighed sample of solid, open stopcock 1, set the mercury a t a, and outgas. Close stopcock 1, admit helium to about 20cm. pressure, raise the mercury to the boxom of B4, and evacuate E . With stopcock 1 still closed, find pV as before; then open stopcock 1 and find Z' by the procedure given above. The density of the sample is then:
D=-
Density By water displacement By helium displacement
2'
where x' is the volume of A' less the volume occupied by the solid, and w is the weight of the sample. DISCUSSION
Adsorbable impurities in the helium are the principal source of error, and some care is required to remove them. It is advisable to admit the helium before use to a bulb external to the apparatus and containing the material whose density is to be measured or one with similar adsorbent properties. After standing for a few minutes in this bulb the helium is admitted t o the apparatus proper through a trap immersed in liquid air or liquid nitrogen. If a chemical drying train is used instead of the cold trap, careful flushing with helium is required. The presence of adsorbable impurities in appreriable quantities will give ab-
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