I N D U S T R I A L A N D ENGINEERING CHEMISTRY
January, 1925
ize the inside and outside atmospheric pressures. In this manner the tubes can be weighed consistently within 0.3 mg., depending upon the accuracy of the balance used. Estimation in Alkali H u m u s
The results reported in Columns 3 and 4 of Table I show that the dilutions indicated did not interfere with the carbon determination. The method is therefore adapted to the estimation of carbon in alkali humus extracts, without the necessity of evaporation, which is attended under certain conditions by loss of carbon, as shown by the following experiment.
85
A 4 per cent ammonium hydroxide soil extract representing a composite solution from the extraction of several differently treated soils was equally divided. One portion was evaporated in copper boats on a steam bath and the second portion in a Hempel dessicator in vacuo at laboratory temperature. In a second case equal portions of humus solution were evaporated in like manner to constant weight in platinum dishes. The carbon was then estimated in the boats by combustion in a furnace. The platinum dishes were ignited over a free flame. The following results were secured: Steam bath Humus carbon, per cent 0.8045 Loss on ignition (humus), per cent 1.6033 Results represent average of four determinations.
Hempel 0.8945 1.7130
The Surface Tension of Crude Oils’ By Ellery H. Harvey BUCKNELL UNIVERSITY, LEWISBURO, PA.
URING an investigation of the method of determining surface tension with the du Nouy tensiometer, a complete set of crude oil samples, representing all the important producing fields of the United States, became available for testing. Such data as are reported herein will be,of interest to the oil technologist and at the same time will indicate the tendency of the du Nouy readings to vary from the results obtained with the more widely known “capillary tube” and “drop weight” methods. Such a comparison is necessary, since there is no recognized standard method of determining this important constant. With over a dozen methods of varying degrees of complexity from which to choose, and the results obtained not being necessarily comparable, it is highly desirable that the technic employed be indicated in reporting any surface tension measurement.
D
TABLE I-SURFACE TENSION OF THE CRUDEOILS OF THE UNITED STATES (Temperature 24’ C.) STATE OIL FIELD Dynes Vew York Allegany County 30.18 ?ennsylvania Mercer County 32 92 Pennsylvania Allegheny County 28.81 Zennsylvania Composite of state 29.16 1,ima 30 87 -Ihio -.. -Corning Ohio 30.52 Indiana Lima 30.87 Illinois Lawrence, Crawford, and other counties 30.87 Kentucky Big Sinkinn 30.87 Kentucky Ragland 32.92 West Virginia Maryland 29.49 West Virginia Eureka 29.49 California Eastside Coalings 34.30 California Kern 37.72 California Sunset 32.92 California Sunset 35.67 California Santa Maria 31.55 California Montebello 35.67 Montana Winnett 27.44 32.24 Wyoming Big Muddy 34.30 Wyoming Salt Creek Colorado Florence 32.92 31.55 Kansas Augusta Kansas Florence, Peabody 31.21 29,83 Oklahoma Billings Oklahoma Ponca 30.18 Oklahoma Cushing 29.83 Oklahoma Pershing 30.87 Oklahoma Hewitt 31.21 Oklahoma Madill 26.76 Texas Burkburnett 30.01 Texas Media 31.21 South Texas Somerset 29.15 South Texas Goose Creek 33.62 South Texas Humble 34.64 South Texas West Columbia 33.62 Arkansas El Dorado 30.18 Louisiana Caddo 30.52 Louisiana Pine Island 34.30 Louisiana Anse La Butte 34.64
The du Noiiy apparatus2 is essentially a torsion balance in which the ring method is utilized, but instead of measuring 1 Received 2
May 16, 1924. J . Gen. P h y s i ~ l . ,1, 521 (1919).
the tension by the time-consuming use of weights, the torsion of the wire is used to counteract the tension of the liquid film and break it. To determine the factor for converting from dial readings to dynes per centimeter, the instrument is standardized with distilled water a t a definite temperature and, since this reading is only about 72, it is assumed that the strain on the wire is proportional to the angle torsion. With pure liquids and in the absence of vibration and temperature fluctuations the instrument in quite satisfactory, no other apparatus being as simple, rapid, and requiring as little material with which to work. When working with solutions, in addition to the foregoing precautions, evaporation must be prevented and the surface renewed. Table I1 furnishes a comparison between the results obtained with the du Noiiy instrument and those obtained with the capillary tube and hanging drop methods. It is evident from the data that the du Noiiy method tends to give results slightly higher than either of the other methods, the results obtained with the stalagmometer being in closer agreement with the du Noiiy results than those obtained with the capillary tube. TABLE 11-COMPARISON
OF RESULTSB Y VARIOUS METHODS (Temperature, 24‘ C.) du Nouy Capillary tube Hanging drop Dynes Dynes Dynes 26.76 23.92 25.64 30.01 27.26 28.81 30.87 27.90 29.57 30.18 27.30 28.86 31.56 28.53 30.30 30.52 27.53 29.27
STATE Oklahoma Texas Kentucky New York Kansas Ohio
For the purpose of determining whether doser agreement could be obtained if pure liquids were compared, the C. P. chemicals listed in Table 111were examined. TABLE 111-RESULTS
LIQUID Aniline Carbon disulfide Chloroform Pyridine Toluene
WITIi PURE LIQUIDS (Temperature, 21’ C.) du Noiiy Capillary tube Hanging drop Dynes Dynes Dynes 46.21 44.89 45.78 36.23 33.11 34.00 31.25 27.63 29.07 40,56 38.27 39.41 32.25 28.80 29.94
While the same relative differences between the methods persist, without a more extensive investigation illustrating to the contrary, it does not seem possible to derive a conversion factor that will apply in all cases.
