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Vol. 17. No. 11
Measurement of Vapor Tension of Gasoline and Other Liquids’ By Harold S. Davis ARTHURD. LITTLE,INC., CAMBRIDGE, MASS.
If A = the original pressure of the air and saturated gasoline vapor If B = the pressure exerted by the mixture of air and vapor after i t has been compressed to half its original volume in the presence of the liquid gasoline If P = the vapor tension from the gasoline Then P = 2 A - B
This method consists in measuring the pressure exerted by a mixture of air and the saturated vapor, and then determining the additional pressure necessary to compress the air vapor mixture to half volume in the presence of the liquid. A n apparatus is described for determining the vapor tension of gasoline by this method. The possible errors involved in the U. S. Bureau of Explosives’ method for determining gasoline vapor tension are reviewed.
Similarly, if the air vapor mixture is compressed to one-third its original volume to give a gage pressure B I , p = 3A - Bt 2 Error Due to Solubility of Air in Gasoline ~
Gasoline undoubtedly dissolves a certain amount of air and at half volume, owing to its increased partial pressure, some additional air will be dissolved from the gas into the liquid. Accordingly, the calculated value of the gasoline vapor tension will be too high by a certain quantity (call it X ) . Similarly, the vapor tension calculated from the pressure after compression to one-third volume will be 2 X too high. It is therefore possible to gain a measurement of X (the airsolubility error) by finding how much higher the calculated value of the vapor tension appears a t one-third volume over that a t one-half. The following values were actually obtained for a sample of “benzine” in the apparatus described herein: Half volume One-third volume
30.1 cm. Hg ( 5 . 8 Ibs./sq. in.) 31.7 cm. Hg (5.1Ibs./sq. in.)
With liquids of greater volatility, where the proportion of air in the air vapor mixture is cut down, the air-solubility error is correspondingly diminished. Vapor Tension Meter
I n order to test the practical utility of this principle in the design of apparatils for measuring the vapor tension of gasoline, a device has been constructed similar t o that shown in the diagram. The container for the gasoline is a metallic cylinder, A , 6.1 cm. in diameter and 28 cm. high. These are the approxi1 Presented under the title “A New Method and Apparatus for Measuring the Vapor Tension of Gaso!ine and Other Liquids” before the Division of Petroleum Chemistry a t the 69th Meeting of the American Chemical Society, Baltimore, M d . , April 6 t o 10, 1923.
into the top, carries a stopcock, c, a tire D,and a pressure gage, F * (There is a piece Of packingin a tire which soon deteriorates on contact with gasoline* It must be removed and replaced by One Of Near the tal' plug, B, fits througll a a bell-shaped mouth into the side of the container.
of the apparatus will be understood from the following directions for its use: DIRECTIONS FOR USE ( 1 ) Filling with gasoline. Place the apparatus on its side with plug B pointing upward; unscrew plug B and pour the gasoline into the bell-shaped mouth until the apparatus is full. Bring the apparatus back to the upright position; the excess of gasoline will run out the mouth, leaving the container full of liquid to the lower edge of the opening. The space above, filled with air and vapor, is about one-tenth of the total volume. ( 2 ) Cleaning. Shake the apparatus for a few minutes, then remove plug B and pour out all the gasoline, throwing it away. Refill the apparatus with a fresh sample of gasoline. ( 3 ) Saturating the air with gasoline at atmospheric pressure. Place the apparatus in a dish of water a t the desired temperature. Shake it with a brisk, up-and-down, jerky motion and vent the stopcock C five times, at minute intervals, t o remove t h e greater part of the air. Then shake without venting until t h e gage reading remains constant for several minutes. (4) Filling the indicator tube with air and saturated gasoline vapor. Hold the apparatus on its other side with plug B pointing downward until the indicator tube is filled with air and saturated vapor. Replace the apparatus in the upright position, and incline i t slightly until gasoline rises in the indicator tube to the lower graduation mark. Tap the gage lightly and record its reading, which should remain steady. This is the first gage reading. ( 5 ) Compressing the mixture of air and saturated gasoline vapor in the zndicator tube to half volume. Attach a tire compression pump a t the valve D and slowly force in air until the gasoline has risen in the indicator tube t o the upper graduation mark. At intervals during the compression shake the apparatus up and down with quick jerks to throw gasoline into the upper part of the indicator tube, and thus avoid the presence there of any deposited liquid of a different composition. The air vapor mixture has now been compressed to half its original volume. (6).Readings and Calculations. The final gage reading a t half volume is the one which remains steady even after prolonged shaking. 76 Vapor tension of gasolinea = twice first gage reading Ibs.) - the final gage reading a t half volume f 1.6 cm. (14.51 g (0.3 lb.)*
+
This is the absolute pressure of the gasoline, not the excess above atmospheric pressure as is registered by the ordinary pressure gage. This addition corrects for the additional pressures on the air vapor mixture in the indicator tube due to the hydrostatic heads of the gasoline
I,VD USTRIAL AND ENGINEERING CHEJIISTRY
November, 1925
( 7 ) Check determinations. Turn the apparatus on its side to refill the indicator tube and proceed again as in 3, 4, 5, and 6.
Results
The following results were obtained in actual tests on an instrument of slightly different dimensions from the one described above: V a p o r T e n s i o n s of Five L i q u i d s as M e a s u r e d in the V a p o r T e n s i o n M e t e r a n d as G i v e n in S t a n d a r d T a b l e s for t h e Same T e m p e r a t u r e s (Pressures in Ibs. per sq. in. a n d cm. of Hg)
TENSION---
--VAPOR Temperature
c.
Av.
23 24 23 24 23, 24.0 25.0
2.5 , B
2 5 . ;7
Av.
25.0
Av.
22.6 23.0 24.0 23.0
Gage reading a t half volumen Lbs.
Tlhiev
X'apor tension meterb Lbs
14.3 14 3 14.4 14.4 ( 7 4 . 4 cm.)
0.3 ( 1 . 6 cm Benzene a n d Tlhter 12.3 (13 2 ) 12.2 12.5 12.6 12.4 2.3 (64 cm.) ( I 2 cm.) Carbon Telrachlo?idu a n d TBalev 12.6
)
Standard tables Lbs.
0.1 ( 2 cm.)
2.2 (11 cm.)
12.3
12.4 12,1 (64 cm.) ~~
~
2.3 (12 cm.)
2.3 (12 cm.)
Carbon Bisu!jdr a n d W a t e u 21.5 Av.
22.2 23.0 22.4
8.5 8.4 s.3 8.4 (43 cm.j
6.3 (33 cm.)
6,6 (34 cm. j
Lidit Fvacfton fvom Cracked Disliilote 7.8 7.2 6.9 6.S 7.1 7.2 7.2 7.5 Av. (37 cm.) . (39 cm.) a T h e first gage readings were all Tero b u t this is not t h e case when dealing with very volatile liquids. b Barometric pressure 760 mm. (14.7 Ibs. per sq. in.). 23 23 23 23 23 23 23
Errors in the Method of the U. S. Bureau of Explosives
A device much used for measuring the vapor tension of natural gas gasolines is the vapor pressure bomb recommended by the U. S. Bureau of Explosives. However, it has been conclusively shown that the divergences between results obtained with this apparatus are very large, even for tests made by one man using the same sample of gasoline and the same bomb each time.2 Accordingly, it is valuable to study the different steps involved in this method and investigate the possible errors contained therein. The bomb consists of a metallic cylinder about 6 cm. in diameter and 30 cm. high. I n the top is an opening into which a pressure gage may be screwed. ( 1 ) Filling the bomb. The apparatus is filled with gasoline either by lowering i t into the storage tank or by withdrawing gasoline and pouring it into the bomb. If the cylinder is reasonably free from the contents of the previous charge, it is not likely that the composition of the relatively large quantity of gasoline necessary to fill the bomb could change enough seriously to affect its vapor tension, even when the filling operation is carried out in a casual manner. (2) Pouring out one-tenth of the gasoline. This step, apparently simple, involves great possible errors. As the liquid is poured out, the free space formed in the bomb is partially filled by vapor from the gasoline and partially by air which rushes in past the gasoline. At the end, atmospheric pressure exists in the bomb because i t is in free communication with the outside, but the 2 Shoemaker, Nul. Petroleum N e w , 17, 87 (1925); Oil Gas J., 23, 90 (1925); Burrell, "The Recovery of Gasolme from Natural Gas," A. C. S. Monograph Series, p. 555.
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relative proportion of air to gasoline vapor in the free space is more or less accidental. I t will depend on the rate a t which the gasoline was poured out, the way the bomb was handled, etc., or, in short, on the extent to which the free space has become saturated with gasoline vapor. Sole-Anderson has recognized this point and developed a modified form of t h e apparatus in which t h e free space of one-tenth the volume of t h e bomb is attained, not by pouring out gasoline, b u t by screwing in t h e gage when the apparatus is still full of gasoline and allowing the pressure developed t o force o u t one-tenth t h e gasoline through a needle valve. T h e free space should then be f u l l of gasoline vapor only. It is evident t h a t t h i s is a much more rational procedure, yet it can be applied only t o gasolines whose tension is greater t h a n atmospheric; otherwise why should gasoline be driven out t o f o r m a free space? Finally, since it 1s applicable only t o gasolines of this high tension-i. e , those which boil a t atmospheric pressure-it would appear t h a t t h e operation of filling the bomb completely with liquid might offer some difficulty except in experienced hands, and t h a t trapped air might easily be left in t h e bomb which would add its pressure t o t h e tension of the gasoline.
13) Screwing in the gage. If the temperature remains constant, the additional pressure developed in the apparatus after the gage has been put in place (gage reading) depends on how far the free space was saturated with gasoline vapor in (2). The gasoline will finally develop practically D its full vapor pressure, but this will not be recorded by the gage, because part already existed when the gage was put in place. (4) Putting in a bath for 5 minutes at 21 O C. (70' F.). If the temperature of the gasoline was not 21' C. then the gage pressure will cnange depending upon (1)the extent of the temperature difference, (2) the proportion G of air t o gasoline vapor in the bomb, and (3) the character of the gasoline. ( 5 ) Momentary aenting after 5 minutes. On venting, a mixture of air and gasoline vapor will rush from the bomb, bringing the pressure again t o atmospheric. The proportion of the air removed from the bomb varies with the gage pressure that had been built up and, as just shown, this was influenced by many factors. Momentary venting will not, of course, remove all the air and the variable amount remaining is the disturbing factor in the subsequent steps. ( 6 ) Putting the bomb in a bath at 38" C. (100' F.) and reading Vaoor T e n s i o n M e t e r t h e p r e s s u r e developed. The A-Container for liquid B-Plug screwing into bell-shaped gage pressure finally registered mouth for filling a n d emptying depends not only on the vapor container tension of the gasoline but on C-Release needle valve the quantity of air in the free D-Tire valve E-Indicator tube with three gradspace. uations (7) Temperature c o r r e c t i o n s . F-Pressure gage Corrections are made to the final G-Metal support and protector for indicator tube reading, for the original tempera- H-Stuffing box for indicator t u b e ture of the gasoline, but there is no evident sound theoretical basis for these and they can be based only on experimental tests.
Finally, it must bc remembered that the gage pressure recorded in tests with this apparatus (or with Anderson's modified form) does not give the absolute pressure in the bomb, but only the pressure in excess of atmospheric. That is to say, a pressure of 12 pounds recorded by this instrument is equivalent to about 26.7 pounds absolute pressure. This is very important because the vapor tensions of pure liquids recorded in standard tables are given in units of absolute pressure.
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As pointed out above, the disturbing factor in the accuracy of the final result with the ordinary bomb is the variable quantity of air which still remains in the apparatus. If it were possible to know how much of the recorded pressure
Vol. 17, No. 11
is due to this air, it would be easy to calculate the true tension of the gasoline. I n a sense, this is what the vapor tension device with a visible indicator tube, described above, is designed to accomplish.
Evolution of Hydrogen Peroxide by Oils on Exposure to Light’ By G. F. A. Stutz, H. A. Nelson, and F. C. Schmutz NEWJERSEY ZINC CO., PALMERTON, P A
USSEL,2 in a series of researches, demonstrated that a number of metals, seeds, roots, bulbs, and oils and resins from vegetable sources affect a photographic plate in a manner similar to light. On placing a sensitive photographic plate in contact with or near such materials, i t is so affected that upon development by the usual method a n image is produced. He produced strong evidence that this action is due to hydrogen peroxide evolved from the materials, which makes the sensitive plate developable. Otsuki3 and Saeland4 confirmed the findings of Russel. The characteristics of the action of hydrogen peroxide upon a photographic plate have been studied in detail by Sheppard and Wightman,s and found to be similar to that of light in every respect. (Other agents, such as ozone, are known to produce the same results.) Baughman and Jamieson,6 besides submitting further proof that the action is due to hydrogen peroxide evolved as a vapor, find the effect with oils to be greatly increased on exposure of the oils to sunlight. They also find that the saturated fatty acids of the oils are inactive and the unsaturated fatty acids, strongly active. Clearly, the phenomenon must be associated with the drying of a n oil. Further, it seems very probable that it should be associated with the entire process of the oxidation of an oil film, from the beginning to the final stage, when it becomes a brittle, nondistensible mass. The present investigation was undertaken because i t seemed possible that a study of this phenomenon would give further information about the mechanism of the action of light on drying oils. I n particular, it also affords ready means for determining whether light is selective in Its action on oils-that is, to what extent the effectiveness of light is dependent on wave length. This information is of special importance because of the present interest in accelerated weathering,’ where
R
1 Presented
before the Section
of Paint and Varnish Chemistry a t the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 to 10. 1925. a Proc. Roy. Inst. Great Britain, 16, 140 (1899-1901); PYoc. Roy. SOC.London, 78,385 (1906), and 80, 376 (1908). 8 J. SOC. Chem. I n d . , 24, 575 (1905). 4 A n n . Physik., [ 4 ] 26, S99
(1908). J . Franklin Inst.. 195, 337 (1923).
J. Oil Fat Ind., 2, 25 (1925). Nelson, Proc. A m . SOL.Tcsling Materials. 22, Pt. 2,485 (1922); Nelson and Schmutz, Ibid., 24, Pt. 2 , 920 (1924). e
7
it is proposed to apply intensified light action (as well as other agencies) in deteriorating organic protective coatings. Obviously, in order to do this effectively, light from the most active regions of the spectrum should be employed. Any test that enables us to determine these active regions will thus be of considerable practical value. Method
The oil is placed in a suitable dish if wet, or on a glass plate if in the form of a dry film. A sensitive plate is placed over it, in a light-tight box, a t a distance of from 0.1 mm. to 2 cm. (usually 5 mm.). The evolution of hydrogen peroxide may be nearly complete within an hour, but the reaction with the film may require 18 hours or more for completion. Warming the plate will hasten this latter reaction. I n these experiments, the plate was placed in contact with the oil for 18 hours and then developed. Eastman 33 plates were used with a standard pyro developer; time of development was 1 minute. Sheppard and Wightmans found that for concentrations of hydrogen peroxide of tfle order of magnitude observed in these experiments the opacity of the image produced is a measure of the concentration. The opacity is the reciprocal of the transmission. The transmission was measured by a special microphotometer, designed by A. H. Pfund. The results given in this paper are in terms of opacity, and are therefore a proportionate measure of the hydrogen peroxide concentrations. The opacity produced by a standard sample of raw linseed oil, after exposure to the quartz mercury light for 5 minutes, has been taken as the basis for comparison. I n order to obtain reproducible results, where exposure to light was involved, the samples were exposed a t a distance - of 36 cm.-(14 inches) from a quartz mercury vapor lamp (horizon t a l Cooper-Hewitt burner) burning a t constant current and voltage. Characteristics of the Effect
Any source of light containing blue or ultra-violet light, as well as sunlight, will increase the effect. Such light is found to be instantaneous in its action and, with some oils, a maximum effect is attained after a few m i n u t e s ’ e x p o s u r e . The h y d r o g e n peroxide vapor given o f f under these circumstances did not discharge an
