December, 1923
INDUSTRIAL ALYDESGIYEERI_vG CHEMISTRY
Calcium, 14.43 per cent, equivalent to 40.00 per cent CaC12; freezing point, 620 O C.
By consulting Fig. 2 a t the proper freez$g point the mixture is found to consist of 40 per cent calcium chloride, 46 per cent sodium chloride, and 14 per cent potassium chloride. These and similar curves are also very useful for the reverse operation-namely, the determination of freezing points of various salt mixtures, especially in connection with the operation of the so-called fused electrolyte furnaces. A
1273
very close control can be kept on the feeding of these furnaces by a systematic follow-up of freezing points. The usual procedure of freezing point determination is to fill a small iron crucible with molten salt mixture, suspend in it a base-metal thermocouple, and record the temperature or freezing point curve on a suitable graphic instrument. Just before complete solidification the couple may be withdrawn from the salt and washed in readiness for the next determination.
T h e Vapor Pressures of Gasolines and Light Petroleum Naphthas' By. F. H. Rhodes and E. B. McConnell CORNELL UNIVERSITY, ITHACA, N.
Y.
has been deviseda whereby PON the vapor presA method for the exact determination of the vapor pressures of some of these errors are sure exerted by a gasoline and naphthas is described, and the vapor pressures of seueliminated. This improved gasoline or a light era1 di3erent types of gasolines and naphthas are measured. method is, however, still petroleum naphtha at or I t is shown that no general relation exists between the vapor pressubject to the error due to slightly above the ordinary sure of a gasoline and its aoerage distillation temperature or its the presence of air dissolved temperatures depend, to a density, and that the presence of air dissolved in the gasoline or in the gasoline. The results considerable extent, the loss naphtha may introduce into the uapor pressure determination an obtained by these methods, which will be incurred when error of considerable magnitude. while they may be of value the material is handled or stored, the internal pressure in estimating the pressures developed in shipping containers used for transporting the developed in shipping containers, do not give the true vapor material, the fire hazard incurred in handling the naphthas, pressures of the naphthas. and the ease with which the gasoline may be vaporized in 8 Private communication from R. P. Anderson. the carburetor of an internal combustion engine. A number of methods for the determination of the vapor pressure of gasoline have been devised, and some information on the vapor prefisures of gasolines has been published. The method commonly used for testing casinghead gasolines and blended gasolines in order to determine whether or not tliey may safely be shipped in tank cars or standard drums, has been described by the U. 8. Bureau of Explosives.' A steel bomb is partially filled with the naphtha to be tested, the bomb and its contents are heated to the temperature a t which the, determination is to be made, and the pressure within the bomb is observed. In order to decrease the error due to the expansion of the air in the space above the liquid, this space is momentarily vented to the atmosphere when the temperature of the gasoline reaches 70" F. This method is subject to several sources of error. Some of the lighter components of the gasoline may be vaporized below 70" F., and the vapors thus formed will escape when the relief valve is opened to vent the expanded air. When the bomb is heated from 70" F. to the temperature at which the vapor pressure is to be measured (90" or 100" F.), the air above the liquid tends to expand, and the increase in pressure thus developed is measured with and not differentiated from the increase due to the true vapor pressure of the gasoline. Some of the air present in solution in the original sample may be liberated when the naphtha is warmed, and tho pressure developed by this liberated air may be measured along with the true vapor pressure. No means for agitating the liquid is provided so that there is no assurance that the liquid and the vapor within the bomb are in true equilibrium with each other. A modification of this bomb
IIJ
A
' I
Received June 20, 1923. Report of Chief Inspector of Bureau of Safe Transportation of E x plosives and Other Dangerous Articles, February, 1916. 1
2
FIG. 1
1274
The relations which exist between the vapor pressure of a gasoline at a given temperature and the other characteristics of the gasoline have been studied by a number of investigators. Obviously, a gasoline with a low average distillation temperature should showarelatively high vapor pressure. Wiggins states that with tfhe lighter fractions from midcontj nent crudes the vapor pressures vary as the Baume gravity. This relationshiptholds true, of course, only when comparing fractions from crudes of similar types. The investigation described in this present article was undertaken for the purpose of determining t h e t r u e vapor pressures, a t m o d e r a t e temperatures, of gasolines and naphthas of various t y p e s . Incidentally, an attempt has been 0 ' 0 20 30 4 0 50 60 70 made to derive some FIG. 2 correlation between the vapor pressures of various gasolines at a given temperature and some of the other characteristics of the gasolines. APPARATUS The apparatus used in this work was a modified form of the apparatus described by Browne and Houlehan5 and by Richardson,e and which has been used by Browne and his coworkers in various investigations. (Fig. 1) A glass bulb of approximately 40 cc. capacity was mounted in a water bath and was connected, through a spiral of capillary glass tubing, with a mercury-filled manometer, C. The bulb was attached to an arm, which was connected to an eccentric so that the bulb and its contents could be shaken vigorously. A fixed zero point was marked on the tube just below the bottom of the bulb. The corresponding zero point on the manometer-i. e., the point at which the mercury stood in the manometer when the mercury in the bulb was at the zero point and when both sides of the mercury column were under atmospheric pressure-was also marked. The corrections to be applied to the zero reading on 0 /0 20 30 40 50 60 70 the manometer to comFIG.3 pensate fQr differences between the temperature of the mercury in the manometer and the temperature of the mercury in the spiral within the thermostat were also determined. 4 8 6
Oil Gas J . , 19, 42, 568 (1921). J . A m . Chem. SOC.,35, 649 (1913). I b i d . , S9, 1828 (1917).
Vol. 15, No. 12
INDUSTRIAL A N D ENGINEERING CHEMISTRY PROCEDURE
All the air was forced out of the bulb A; then about 15 cc. of the sample were drawn into the apparatus. After closing the stopcock D, the leveling bulb B was lowered until the gasoline began to boil vigorously under the reduced pressure. The leveling bulb was then raised until the sample was under slightly greater than atmospheric pressure. The vapor recondensed and redissolved in the liquid, b-ut any air which had been liberated during the boiling-out process remained unabsorbed and could be removed by opening the recondensation, stopcock above. This cycle of boiling, -, and removal of the liberated air was conI 1 tinued until no more air was set free-i. e., 800 until the vapor recondensed completely 700 when the pressure was raised. 600 After the removal of the dissolved air 500 the water in the thermostat was brought 400 to the exact temperature at which the 400 determination was to be made. The level- 800 ing bulb was lowered until the mercury /OO within the apparatus stood at the zero 0 /o 20 30 40 point. The bulb was FIG.4 shaken vigorously to establish equilibrium between liquid and vapor and to insure that the liquid and vapor within the bulb were at the same temperature as the water within the thermostat. The leveling bulb was adjusted from time to time to keep the level of the mercury a t the zero point. The agitation was continued for several minutes after there was no further change in the level of the mercury. The reading of the manometer was then taken, and from the barometric pressure and the difference between the manometer reading and the zero point on the manometer the vapor pressure of the gasoline a t the temperature of the thermostat was calculated. (All manometer readings were, of course, corrected for the difference between the temperature of the column of mercury within the thermostat, and for the weight of the layer of gasoline above the mercury within the bulb.)
-r
Jo
TESTSFOR ACCURACY OF METHOD In order to determine the accuracy of this method of determining vapor pressures, a series of runs was made using pure water at various temperatures. The results obtained agreed to within 1 mm. with those given by Regnault. The gasolines and naphthas which were examined were as follows: SAMPLE 1 2
3 4
5
7 8 9
10 11
DESCRIPTION
Straight-run petroleum naphtha, Pennsylvania Oil Co., used for blending with casinghead gasoline Absorption (casinghead) gasoline from the Pennsylvania Oil Co. Blended gasoline, from absorption gasoline, from the Pennsylvania Oil Co. Crude naphtha fraction, from paraffin-base oil, from the Conewango Refining Co. Crude gasoline fraction, from paraffin-base oil, from the Conewango Refining Co. Absorption gasoline from the Mars cO. Absorption gasoline from the Mars Co. Motor gasoline (Texaco) purchased on the market Motor gasoline (Socony) purchased on the market Special gasoline from the Atlantic Refining Co. Special gasoline from the Atlantic Refining Co.
INDUSTRIAL AND ENGINEERING CHEiMlSTRY
December, 1923
.. .. . . . . .. . .... .... ... . 10
Sample. . . Specific gravity a t 15.5' C.. . . Degrees Baume a t 16.5' C.. Size of Sample cc 20 ~.
30 40 50 60
70 80 9c
Dry
TABLE I-VAPOR PRZSSURES OF GASOLINES AND 1 0.764
2
3
0.672
0.679
53.2
78.3
76.2
62 115 132 145 153 160 168 175 185 202 218
26 43 52
119
25 36 44 53 64 86 111 144 191
it+
212
61
70 79 90
100
...
4 0.763
5 0,733
The density (at 15.5" C.) and the distillation range of each of these samples were determined following the procedure described in Bureau of Mines Technical Puper 298 (1922). The results are shown in Table I. The vapor pressures of the various gasolines and naphthas (air-free) were determined. The results are shown in Figs. 2 and 3. ERROR CAUSEDBY DISSOLVED AIR A few c>xperimentswere also made to determine the approximate magnitude of the error which may be introduced by the presence of air in solution in the gasoline. Samples of the original gasolines were introduced into apparatus and their vapor pressures were determined before removing the dissolved air. The air was then boiled out as described above, and the vapor pressure of the air-free material was determined. The results are shown in Fig. 4. It will be observed that the presence of the dissolved air introduced a very considerable error. The exact magnitude of the error from this source will depend, in any specific case, upon the amount of air present, the nature of the gasoline, and the method by which the vapor pressure is determined.
3-APHTHAS
6
53.5 61.0 Distillation Temberature 104 65 124 85 131 91 137 97 145 103 152 107 160 112 169 117 182 126 20 1 144 237 175
7
0.664 80.8 F. Start 30 38 43 46 50 55 62 76 88 111 141
0.670
5
8
0.744
9 0.743
10
0.731
11
0.723
79.0
58.2
58.4
61.5
63.6
24 42 51 60 68 78 89 98 118
42 75 90 106 112 135 146 I55 167 190 221
40 75 94 105 115 125 135 146 162 182 215
29 79 101 116 129 133 152
39 78 91 99
iSi
161
175 204 217
105
112 116 129 140 159 194
particularly some of thosz containing casinghead gasoline, show abnormally high vapor pressures, while the sample of crude naphtha fraction (Sample 4) showed abnormally low vapor pressures. It is evident that the vapor pressure cannot in every case be predicted, even approximately, from the density. RELATIOX BETWEEN DISTILLATION TEMPERATURES AND VAPORPRESSURES From a comparison of the data for the distillation ranges and the vapor pressures of the various samples it will be noted that, as might be expected, the samples with a relatively low average distillation temperature show relatively high vapor pressures, and vice versa. The relation between distillation temperatures and vapor pressures is, however, not sufficiently definite and uniform to permit the accurate prediction of the vapor pressure from the distillation data.
Portable Desk and Reagent Carrier
RELATION BETWEEX DENSITIESAND VAPORPRESSURES The relation between the densities (at 15.5" C.) and the vapor pressures (at 20" C. and 40" C.) of the various gasolines and naphthas is shown by Fig. 5. It will be observed that, in general, the samples with the lower densities show the higher vapor pressures. I n most cases there appears to be a rather definite relation between the density and the vapor pressure a t any given temperature. Some of the samples,
FIG.
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'I h'e accompanying illustrations show two u n i q u e conveniences several of which are in use in Lehn & Fink's laboratory-a portable desk and chair and a teawagon reagent carrier. The desk is adjustable and contains a drawer for notebooks, etc. The tea wagon offers a convenient and quick means of having a t hand a set of reagents a t any particular place in the laboratory where the chemist happens to be -. working. 1
