312
Vol. 63
NOTES
lation of the anhydrous acetone, was unsuccessful. Use of the acetone-urea comples7 did not appear promising. The authors were, however, able to obtain high yields of acetone with an average density a t SO.OOo of 0.78994 f 0.00003 g./ml., using a synthetic zeolite as a desiccant, followed by distillation with ordinary equipment.
pares favorably with the 1.35596 & 0.00003 reported by Thomas and R’lcAllister.’ Although the reproducibility of the densit’y results was within the precision of the method (* 0.00005 g./ml.), the accuracy of the results is claimed only to f 0,0001 g./ml. because of the difficulty of precisely evaluating the purity of the acetone. The assumption for insignificantly low water content of the samples is based on the idenExperimental tity of samples prepared by the method from difMost reagent grade acetone is unlikdy to contain significant impurities, with the exception of water; “Baker An- ferent starting materials, and the failure of SYCalyzed” reagent grade material (J. T. Bakcr Co., Phillips- cessive repeated applications of the desiccatlon burg, N. J.) was found to be a particularly suitable starting procedure to change the measured properties. material, with a water content of about 1.2 mole yo. The Density and refractive index were the analytical synthetic zeolite Type 5A Molecular Sieve (Linde Air Prod- methods for evaluating both these criteria. In ucts, New York, N.Y.) was regenerated by heating a t 670’ F. for 3 hours in an air oven: the hot material was sealed addition, the assumption of the absence of any and allowed to cool. This regenerated material was added impurity other than water appears valid in view of to the starting acetone in a weight ratio of 1 part Molecular the close correspondence of both density and reSieve to 7 parts acetone; this amount represents a 3- to 4fold excess over the calculated capacity of the zeolite. If fractive index values of acetone from these prepathis operation is carried out in the flask to be used for Rub- rations to those reported for material prepared sequent distillation, the possibility of water contamination through processes employing more rigorous sepafrom the atmosphere during future transfer operations is 01,ration techniques. It seems improbable that any viated. The mixture was allowed to stand 18 to 24 hours, with occasional swirling, and then was quickly connected t o significant impurity would remain undetected by a Vigreux column equipped with a straight water-cooled con- both analytical methods. denser and receiving flask, all of which had been purged with Acknowledgment.-This work was carried out a steam of CaS04-dried air to remove water adsorbed on the with funds made available by the National Science glass surfaces. All junctions were non-lubricated ground glass joints, and the apparatus was vented through a CaSOI Foundation, and the authors gratefully acltnoxldrying tube. The center cut, comprising 80 to 90% of the edge this support and encouragement.
starting volume, was collected. This material had a density of 0.78993 g./ml. Using this sample, the entire desiccation procedure was carried out a second time, with fresh Molecular Sieve, and the twice-treated distillate had a density of 0.78996 g./ml., indicating that no further drying had been effected. An additional preparation, from another sample of “Baker Analyzed” acetone, had, after one desiccation treatment, a density identical t o those reported above. The refractive index of the various preparations was similarly constant. The densities were determined using the apparatus and procedure described by Thomas and McAllister,’ with the modification that all glass surfaces were thoroughly dried with a CaSOrdried air stream, and exposure of the acetone t o ordinary air at any point during loading of tho pycnometers was eliminated. Refractive index measurements were made using a Bausch and Lomb precision refractometer capable of giving results accurate to f 0.00003 unit.
TABLE I THE DENSITY OF ANHYDROUS ACETONE Temp.
Density (dml.)
(OC.)
20.00
0.78989 .78997 .78906 .78419 .78426 .78429 .76943 .76944 .75482 .75481
25.00
37.80 50.05
Results and Discussion The densities given in Table within d=O.0lo. this acetone was
of the desiccated acetone are I. Temperature control was The refractive index ( n Z 5 ~ of) 1.35589 0.00003, which com-
+
(7) W. Schlenk, .Jr., A n n . , 666, 204 (194Q): 0. Redlich, C . \I. Gahle, A. IC. Dunlop and R . \V. Alillar, J. Am. Chem. Soc., 78, 4153 (IOXIj.
T H E EFFECT OF DROP SIZE ON THE ACCURACY OF SURFACE TENSION DETERMINATIONS BY THE SESSILE DROP METHOD BYEDWARD B. DISMUEES Southern Reaearch Institute, Birminpham 6 , Alabama Received Aupust 1.8, 1968
A classictzl method for determining surface tension, particularly of molten metals and salts, is the sessile drop method. If a liquid drop rests on suitable flat surface and assumes an obtuse contact angle, the dimensions of the drop silhouette, namely, the maximum radius r and the distance h from the maximum diameter to the vertex, are determined by gravitational acceleration 9, the liquid density d and the surface tension y. No analytical solution of the differential equations that relate these quantities has been obtained, but the surface tension may be calculated from approximation formulas such as the Worthington formula’ y
=
h2gd/(l
+ 0.6094 h / r )
(1)
or from the Bashforth and Adams tables.2 The use of these tables has been reviewed by Ellefson and Tay10r.~ IGngery and Humenik4recently pointed out that the accuracy of surface tension determinations by the sessile drop method becomes less as the drop (1) A . M. Worthington, Phil. Map., 20, 51 (1885). (2) F. Bashforth and S. C. Adams, “An Attempt to Test the Theories of Capillarity,” Cambridge University Press, 1883. (3) B. 9. Ellcfson a n d N. W. Taylor, J . A m . Ceram. Soc.. 21, 193 (1938). (4) W. D. Kingery a n d ill. Humenik, Jr., THISJOURXAL, S7, 359 (1‘333).
Feb., 1959
NOTES
becomes more spherical owing to small volume, high surface tension, or low density. Baes and I
