Measurement of Density of Hydrocarbon liquids by the Pycnometer H. M. SMITH AND COOPERATORS, Bureau of Mines, Bartlesuille, Okla.
’
NE of thc most important physical properties of a hydrocar-
tee of Technical Committee D2 of the American Society for Testing Materials, has been working for a numbe; of years on the development of analytical methods for hydrocarbon groups in petroleum products, particularly of the distillate class. In connection with developmental work on methods by this committee, the need for accurate methods of deterniining density and refractive index frequently arose and, therefore, Section D of Research Division IV was established to study methods for determination of dentcity and refractive indes. One of the first duties of this committee was to develop or standardize a method for determining density which would be accurate to a t least 0.0002 gram per ml.
bon or hydrocarbon mixture is its densi,ty. I t is one of the criteria upon which the identification and purity of individual hydrocarbons are based, and it is also of importance in a number of calculated properties, such as specific dispersion, refractivity intercept, and specific refraction, and in the calculation of kinematic and absolute viscosities from each other. As hydrocarbon research develops more precise methods of estimating the quantities of a given component, the necessity for more accurate physical properties becomes very urgent. Not only must these properties be determined accurately, but they must also have excellent precision within a given laboratory (repeatability), and between laboratories (reproducibility); the met.hod should also be capable of relatively rapid application. Research Division I V on Hydrocarbon .4nalysis, a subcommit-
Table 11. Cooperative Data Obtained with A.S.T.M. Bicapillary Pycnometer for Toluene Laboratory
6D
-
D 09 to I I, Uniform to 0 I Percent
E F
Throughout Scale
G
B I J
0 D . - 6 0 Mor.
Av. of all results
4 5 2 0 5 MI Copocity,
0 D -Approx 20
Figure 1. Open-Arm Bicapillary Pycnonieter A l l dimensions in millimeters. Material, borosilioate glass. Weight, 30 grams max. Graduation lines extend around entire circumference of pycnometer a t integral numbers half-way around a t half divisions
Table I. Cooperative Data Obtained with A.S.T.M. Bicapillary Pycnometer for Isopentene and Gasoline Reid vaporpressure Gasoline
la-P,&d Lab, A B
C D E I
density
o,6197 0.6196 0.6199 0.6196 0.6197 o,g197
;:g:
Isopentane No. of Av. debns, deviation +lb
3 3 3
0
0
i
Av:
density
+I +1
detnn,
o,6615
2
0.6614 0,6615 0,6614
4 3 3
A;::
+: 0
No. of
7; ::::;!
Av, deviation +lb
+: 2 1 0
o +1
0
; 4;
+zc
7; +I
1-2 +1
$:
-1 0.6194 B I -2 0.6612 4 I -2 J 0.6198 *3 0 +2 0,6614 3 0 0 +I Av. of all results 1 , +1 0,6614 35 0.6196 35 1 Mas. dev. of lab. av. . . +3 .. -3 +3 0 Average deviation X 104 of laboratory’s results from that laboratory’s average density. b Deviation X 104 of laboratory‘s average from over-all average. c Deviation X 104 of Laboratory’s average from value furnished by National Bureau of Standards, 0.6613.
.
0.8654 0.8653. 0.8654 0,8652 0.8652 0.8652 0.8652 0,8652 0,8653 0.8k53
Commercial Toluene No. of detns. Av! Deviation
3 3 2
05
2 2
0
1
2 2 3 20
0 1
..
0 1
1 0 1
+I*
0 +I -1 -1 -1 -1
-1
0
Maximum dev. .. .. +=1 of lab. av. a Average deviation X 10‘ of laboratory’s results from that Laboratory’s average density. b Deviation X 104 of laboratory’s average from over-all average.
Short Lines ot Eoch I Mnl. Longer Llnes ot Eoch 5Mm Numbered os Shown
Av.
Av. density
Among the methods considered was a pycnometer method, developed by Lipkin et al. ( 8 ) . , According to the authors, this method gave results, within a given laboratory, having a precision of +=0.0001gram per nil. and a probable accuracy of the same magnitude. In the use of these pycometers it was felt that the types of compound which would be most susceptible to error probably would be those that are relatively volatile, inasmuch as this instrument relies upon an open capillary to control diffusion of the lighter materials. Therefore a series of cooperative tests was arranged among ten laboratories, using the U-shaped open-arm bicapillary pycnometer, shown in Figure 1. For comparative purposes, the Bingham pycnometer, which is a standard inst,rument used by many laboratories, and the fifth-place Chain-o-matic specific gravity balance were concurrently tested. The test materials selected were: (1) pure “isopcntane” (2methylbutane), which was selected primarily to give an indication of the accuracy that might be expected; (2) a 12-pound Reid vapor pressure gasoline, which would give not only indication as to the repeatability and reproducibility of a sample within given lab+ ratories and between laboratories, but also an indication of accuracy. This latter feature was possible because the density of this gasoline was especially determined a t the National Bureau of Standards, so that a value accurate to O.OOO1 gram per ml. w a s known. In addition, the densities of several samples of relatively pure aromatic compounds were determined. These compounds were not so voiatile as the two previous samples, but gave indications of repeatability and reproducibility in a somewhat higher boiling range. Tables I and I1 show the deviations obtained in some of these cooperative tests. These tables substantiate the results reported by Lipkin et al., in that, except for laboratory D, the average devirttion of each laboratory’s results from its mean value waa
1452
1453
V O L U M E 2 2 NO, 11, N O V E M B E R 1 9 5 0 *0.0001 gram per ml. or less for both isopentane and the 12pound gasoline. It is also true that the individual determinations (not shown in table) of a given laboratory did not deviate from each other in most instances more than their average deviation froin the over-all average. For elample, out of 35 individual determinations on the 12-pound gasoline, 30 deviated from the laboratory average by either 1 or 0 in the fourth decimal place, four had a deviation of 2, and in only one was a deviation of 3 in the fourth decimal place reported. Similar conclusions apply also to the tests made with isopentane and the commercial toluene. With regard to reproducibility between different laboratories, the results seem to indicate that a value of +0.0002 is satisfactorily established, inasmuch as only one out of ten laboratories cooperating reported a value higher than this. Here again, out of 35 determinations on the 12-pound gasoline, 20 had a deviation of 2 or less in the fourth decimal place, 0 a deviation of 3, and none was higher. Similar observations can be made on the data obtained with isopentane and commercial toluene. I t was the committee’s opinion that if 90% of the laboratories could achieve this degree of repeatability and reproducibility, it could with safety indicate those limits as being applicable to the method. Regarding accuracy, A.P.I. Research Project 44 tables givc the density of pure isopentane as 0.61967. The average value shown in Table I for the 10 laboratories is 0.6196. This would indirate that the accuracy was of the same order of magnitude as the repeatability, or 0.0001 gram per ml., especially as the deviations of the individual determinations were of comp~rablevalues This is further borne out by the average value of 0.6614 ohtained for the 12-pound vapor pressure gasoline as determined by the cooperating laboratories, compared to the National Bureau of Standards value of 0.6613. This again confirms the opinion.that the accuracy of these data is comparable with the precision. Cooperative data for the Bingham pycnometer indicated simi-
lar precision and accuracy. This device, however, requires simple accessory equipment for easy cleaning and a hypodermic syringe for convenient filling. The data obtained with the fifthplace Chain-0-matic specific gravity balance, when used under carefully controlled conditions by laboratories which were familiar with its use, indicated that it was also capable of excellent accuracy and precision. However, as this instrument is not commonly found in most petroleum laboratories, its standardization by the comrnittec was not considered. Bssed on the results of the cooperative testing, part of which is reported in Tables I and 11,the committee has standardized the U-shaped bicapillary pycnometer, described by Lipkin et al., and it is now an A.S.T.M. standard method ( I ) . It also has an American Standards Association designation (I). ACKNOWLEDGMENT
Cooperators in the preparatiorl of this paper were: R. C. Alden, Phillips Petroleum Company; E. L. Baldeschwieler, Standard Oil Development Company; G. R. Bond, Jr., Houdry Process Corporation; L. M. Henderson, Pure Oil Company; S. S. Kurtz, Jr., Sun Oil Company; Louis Lykken, Shell Development Company; Harry Levin, Texas Company; Robert Mattason, California Research Corporation; E. T. Scafe, %cony-Vacuum Oil Company; C. E. Starr, Jr., Esso Standard Oil Company (Louisiana); and M. J. Stross, Universal Oil Products Company. LITERATURE CITED
(1) Am. SOC.Testing Materials, “A.S.T.M. Standards,” Part 5,
1102, Designation D941-49, 1949; Am. Standards Assoc.. Designation 211.62-1949. p.
(2) Lipkin, M. R., Davidson, J. -4., Harvey, W. T., and Kurta, S. S., Jr., IND.ENG.CHEM.,. ~ N . A I . ED., . 16,55 (1944). RECEIVED February 10, 1950.
Determination of Relative Specific Surface of Zinc Oxide Pigments WARREN W. EWING
AND RICHARD N. RHODA Lehigh University, Bethlehem, Pa.
hRIOUS methods have been devised for determining the Vsurface area of finely divided solids, but the agreement among methods as to the values of such areas is not good. The disltgreement may &-attributed to fundamental weaknesses in the method or to the fact that different area characteristics are measured. The microscopic method is an example of fundamental weakness; here there is a large degree of uncertainty as to whether the operator is nieasuring the distance between the actual edges of a crystal or an optical illusion due to refraction :,iiigs, poor resolution, etc. .$rea characteristics are governed hy t.he use to which the solid is subjected. If the solid is to be used as a catalyst in a gas phase reaction, the Brunauer-l~mniett-Teller gas adsorption method using an adsorbate of :t na-ture similar to the gas adsorbed I)y the catalyst is indicated. But if the solid is t o be used in a liquid medium as in the compounding of paints, rubber, etc., it method involving the adsorption of a n adsorbate in it liquid might give it truer picture of the csh:iracteristic area pertinent to such a system. If an absolute value of a surface area is desired, the method of Harkins and Jura (6) is available. Harkins and Gans ( 5 ) have studied ;he adsorption of oleic acid on titanium oxide from it benzene solution. Ewing ( 8 ) has shown that the specific surfaces of various zinc osides can be determined by adsorbing methyl stearate and glycol dipalmitate from benzene solutions. Smith and Fuzelc ( 7 ) determined the
surface area of nickel and platinum catalysts by adsorbing fatty acids from organic solvents. The presence of water interferes seriously with‘ adsorption from organic solvent,s, and the necessity of carefully drying both pigments and solvents makes the procedure tedious. The method presented here for determining the surface areas of pigments by adsorption from aqueous solutions eliminates the tedious drying procedures, thus shortening the time of operation and making the method adaptable tjo practical application. The area. obtained by this method should be the characteristic area desired for pigments dispersed in liquid media. EXPERIMENTAL
The zinc oxide pigments wert’ obtained from the New Jersey Zinc Company of Pennsylvania. Quantities of the samples were placed in large evaporating dishes ttnd washed with several portions of carbon d i o d e - f r w w:ttrr hy stirring and decanting the liquid. The slurries wcrc d&tl in a n oven st 100’ C.; the pigments were then pulverized hy crushing thr lumps with t,he fingers or hy gently grinding in a moi,tar. Electron micrographs and electron diffraction patterris of representative samples (I) showed negligible conversion of tht. surface of the oxide to carbonate in washing. The washing apparcntly removed foreign material from the pigmcnts; in some cases the d j t a for the washed samples gave surface valuc.s which were much nearer the values expected from the electron microscope data. Electron micrographs of the pigmrnts befo1.e and aftcr washing showed no allparent change in the surface nrcn dur to the washing.
