INDUSTRIAL
AND
ENeINEERlNG CHEMISTRY PUBLISHED BY C H E M I C A L SOCIETY W A L T E R J. M U R ? H Y , EDITOR
Laboratory Tests to Predict the Performance of Metals under Service Conditions D. W. SAWYER
AND
R.
B. MEARS, Chemical Mebllurgy Division, Aluminum Research Laboratories, N e w Kensington, PI. fuels themGlves, even in the presence of water, were inert to aluminum. Some other factor or factors must have caused the attack under service conditions.
To predict the performance of metals under service conditions, a laboratory test must give results that correlate directly with service results. The most certain method of designing a suitable taboratory t a t is to simulate the conditions of service as closely as possible. Attempts to accelerate the laboratory test by intensifying one of the facton encountered in service often load to misleading results. Several examples of laboratory tests illustrating these points are described.
Therefore, a new test was run. Open boxes were constructed of aluminum alloys. These boxes included torch-welded, spob welded, and riveted joints to simulate the construction of actual gasoline tanks and were equipped with cast fittings like those used in the actual tanks. Since the previous test had indicated that the various fuels, even in the presence of distilled water, had no action it was decided to use a typical leaded aircraft fuel plus a 3.5% sodium chloride solution in distilled water. The gasoline layer waa changed every week and the sodium chloride solution was changed every month. After one year it was apparent that corrosion had develo ed, but the type of attack obtained was not similar to that wkch had occurred in service. Therefore, the test was not considered to be dependable.
T
HERE are several different reasons why engineers often
desire to predict, on the h i s of laboratory tests, the behavior of some specific metal or alloy under definite conditions of service (7). Such predictions are particularly desirable when equipment is required for some new chemical or process about which no service background has been built up. /Laboratory tests are also helpful in determining whether some untried metal or alloy offers promise of being more suitable than the material previously used. Laboratory tests are often useful in determining the cause of attack which has been encountered in service and in developing methods to prevent or alleviate this attack. These u ~ e 9of laboratory corrosion tests are fairly well known. They are concernec with the effect of the product under consideration en various metals or alloys under the conditions of service. However, often it is of importance to determine the effect of the metal or alloy on the properties of the product being processed. &ch teats have not been described so frequently. In the present paper, tests of both types are described. In the past, much emphasis has been placed on accelerated corrosion tests. All engineers would like to be able to evaluate the relative behavior of various metals or alloys in a matter of minutes instead of weeks or months. However, technical people are now beginning to realize that results from tests “accelerated” by altering certain factors encountered in service will generally lead to false conclusions. I t is becoming axiomatic that the more closely the laboratory test conditions approach the conditions of service, the more dependable the results will be. The teats described below illustrate the validity of this axiom.
I n the meantime, with the cooperation of the aircraft operators, it was found that an aqueous phase collected in the bottom of the particular tanks in servioe and that these tanks were designed so that it waa impoesible to remove this entrapped liquid completely. An attempt wag made to collect samples of thiB watery layer. Draining8 from individual tanks after each flight gave from a few dro s to a tables onful of this liquid. These drainings were accumurated until a R u t 5 gallons were obtained. A new &Et was started using small enclosed aluminum alloy boxes provided with all the features of the service tanks. The boxes wem equipped with cast fittings and breather vents just as are the large tanks. A small portion of the tank drainings was laced in each small tank and then these tanks mere partially B e d with leaded aircraft fuel. The tanks were installed in a delivery truck so that they could be agitated in a manner somewhat similar to that under service conditions. In addition, the gasoline layer was changed every week and the aqueous layer every month. When all these precautions were followed, test remlts simulating those of service were obtained. Once a dependable test waa available, it was possible to evaluate various alloys, types of construction, and other factors and thus to find a solution to the problem. This is probably an extreme case, but it will illustrate the necessity for duplicating the conditions of service if a dependable laboratory test is to be obtained.
GASOLINE STORAGE TESTS
Airplane gas tanks made of aluminum alloys have been widely used, and in general, have given very eatisfactory service. However, in tanks of a particular design, corrosion was encountered after about one year’s service. In order to determine whether the newer fuels being used in these tanks were responsible for this attack, a series of tests was conducted (9) in which strips of several aluminum alloys were exposed in glasa bottles to the various fuels in both the presence and absence of liquid distilled water. In no case were the specimens of any of the aluminum alloys appreciably attacked after one year’s exposure. Evidently the
MUTUAL EFFECT OF GASOLINE AND METALS
I n selecting a material for the construction of storage tanks or shipping containers for fuels, it is important to select one which has no deleterious effect on the fuel. There are several published references to the effect of metals on the rate of gum formation in fuels contacting them, but most of them tests were conducted a t elevated temperatures (11, 16). It is by no means certain that 1
' " 3 U S TR I A L A N D EN G IN EERIN G CHEMISTRY
2
Ti
he discoloration of the gasoline in con:aused by heavy gum formation. aluminum specimens showed no evied no more alteration in properties of with glass alone,
lines ithr Alun ""D
Initial iD./lOO
GaS0li"e
3.110
Blanks'
2S-I/.Hb
Straight run Cracked Blended
Sfriiighf run. leaded
0.2 6.2 2.2 1.0 5.2 2.4
0.4
0.2
3.2 2.3
Steel Copper
steel MUTUAL EFFECT O F OILS AND METALS
Mp. pm 100 m1.
mi.
7.6
7.2
0.8 Cracked leaded 2.5 5.6 Blended: leaded 1.8 3.2 * Blanks stored in contact with glass. Commereislly pYre aluminum. 0.6
5.2
0.6 4.6
3.2
0.2 1525.8 31.2 2.0 1724.0 144.0
0.2 9.2 1.4
...
6.4 3.4
*
Table II. Induction Period of Garoliner before and after Storage for Five Months Find A1"mi""m
Stainleas
SllOY
Gasoline
Initial
Blanks"
2S-'/,€Ib
Iloliis
Holrrs
Hours
Cracked g.0 2.75 Blended 4.0 Cracked.1eaded 3.6 4:O Blended,leaded 4 . 7 5 5.25 Blanks stored in contact with g1a.s. I , Commerclrlly pure alumiaum.
3.0 4.25 4.0 5.5
Vol. 17, No. 1
Steel Copper Hours Hour 3.5 0.25 4.5 0.5 4.0 0.5 6.5
0.5
steel
Hours
3.25 4.5 3.5 5.25
A somewhat similar study is being made of the mutual effectof lubricating oils and metals, employing B method of testing similar to the proposed A.S.T.M. method for studying the oxidation characteristies of steam-turbine oils (5). Instead of the wire eoii used in the A.S.T.M. test, sheet specimens (10 X 15 em. in size) of several different metals bent in the farm of square tubes have been substituted. The surface area of these tubes was similar t o that of the wire samples ordinarily employed-that is, 1 sq. em. of metal per ml. of oil. Sheet specimens were used instead of wires, since wires of small diameter are affected to B much greater extent in certain environments than are flat surfaces (le). Moisture -'as supplied to the oils, since in service moisture will generally be present. In tests being run st 90" C., 20 ml. of distilled water were added to each s a p : ? of 100 ml. of oil. In tests run a t 120' C . the oxygen, which was bubbled through the oil samples, was saturated with distilled water. The tests were run in glass tubes 600 nun. long and 45 mm. in diameter, each equipped with an individual condenser. The volume of ail used in each tube was 300 ml. Oxygen was bubbled
the relative behavior of the different metals would he the same a t high temperatures as a t room temperatures, yet storage oontainers are used a t room temperatures. For this reason, a lest WBS run under conditions simulating those of storage.
Some of the results are given in Tables I, 11, and 111. These results indicate that cracked or blended fuels are definitely affected by contact with copper. It can he Seen in Table I that the effect of copper on gum formation is most pronounced. The effect of copper on the oxidation induction period is also definite, sa shown in Table 11. Although the effect of copper on 'the octane numhers of the fuels was appreciable (Table III), the magnitude WBS le= pronounced than in the ease of the gum formation or oxidation induction periods of the fuels. No definite changes in the other measured properties were detected, so these are not reported here. The gasoline stored in contact with the other metals WBS not affected, as judged by these property measurements. However, the gasoline stared in contact with low-carbon steel became 6lled with finely divided rust particles. Figure 1 shows the appearance of the steel specimen a t the conclusion of the test. The heavy rust layer which formed hetween the coil turns is e l w l y shown. Figure 2 illustrates the aluminum and copper specimens at the
Figure 1. Steel Specimen after Five Months' Exposure to Gasoline and Distilled Water N o k hewv tun iwer which h s d brlnen the .Oil
tYrnl
~
Tablolll.
Octane Numbomof Garoliner beforeand after Storage for Five Months with Metals Final Alum$-
73:4
72.2 63.8 72.9
stamless Steel Copper ateel 51.1 50.2 61.1 73.1 67.6 73.0 64.3 63.2 64.8 72.7 71.9
SU.3
IJ.,
OL.'
""nl alloy
Gaaaline Straight r u Craoked Blended Straightrun.1eade.d C,+e$.+$ed I)le"(lea.LeS(le(l
Initla1 57.0 76.0 68.3 75.3
85.;
01.0
Blanks- 2S-V.Hb 7312
83.3
Blanks stored in oonlact with glass. b Commercially pure aluminum.
a
60.6
83.3.
83.1. 15.i 11.1
!a:$
0Y.O
ANALYTICAL EDITION
January, 1945
3
slight and rhe oil exposed in contact with aluminum alloy 5 2 s l/&l was aEected no more than the oil exposed in the absence of any metal. The tests being run at 90' C. are giving qualitatively similar results. The oil in contact with copper was definitely affected after 8 days, and marked sludging occurred (Figure 3). No sludging developed in the case of oil exposed to the other metal specimens. After degreasing, the appearance of some of these other specimens at the conclusion of the test is shown in Figure 4. The steel was definitely rusted and the tinplate was attacked near one edge. The zinc showed a few shallow corroded grooves and the other two specimens (aluminum alloy 1 4 S T and stainless steel) showed only a mild surface staining. The interpretation of these test results in terms of service iS not known. However, qualitatively similar results were ohtnined by Hunter and eo-workers (10) under conditions more nearly simulating those of service. It would he expected that where oils are used a t elevated temperature, in the presence of air and moisture, these test results would correlate qualitativdy with service performance. CATHODIC PROTECTION TESTS
Fisure 2.
SDocinrns at Conclusion of Test
Table IV. Oxidation of a Solvent-Refined Pennsylvania Lubricating Oil at 120" C. in Presence of Moistare and Various Metals Metal Unoddised oil
Hours Oxidized
Neutralization
Number
1544
NOmetal
0.05 0.78
1.35 1344 Aluminum alloy 14s-TO 1.08 1344 Aluminum alloy 2S-Ob 0.80 1344 Aluminum alloy 52S-1/zHc 2.70 117 Copper 1.05 1344 Zi,X 2.13 412 Low-carbon steel 1344 1.23 stain1es.steei 1.48 1344 Tinolate a Aluminum slloy. nomind oompoaition: 4.4% Cu. 0.8% Si, 0.8% Mn. 0.4% Mg. b
Commercisily pwe al?mioum. Aluminum aiioy. nommal cbmpoaition: 2.5% Mg. 0.26%
Cr.
the conclusion of the test, other properties of the oil samples. such as interfacial tension (du Noiiy method), steam emulsion number (e), A.S.T.M. color number. (l),,and viscosity (S) were also determined and the ehanees in weiaht .. - or ameaxance of the metal samples were noted. At the present time, one series of tests bas been completed, in which a solvent-refined Pennsylvania lubricating oil was used and the tests were run at 120' C. (Table IV). Another series of tests at 90' C. has hien started.
Figure 3. Sludge
~
I n the test run a t 120' C., it was found that copper definitely increased the neutralization number of the oil after 117 hours' exposure, so this sample was removed from test (seeTable IV). The oil in contact with the low-carbon steel sample r$n for 472 hours, after which time ita nentralin;ation number was markedly increased; it was therefore removed from the test. The other samples were continued in test for 1344 hours. A t the end of this extended period of exposure, it was found that the neutralization numbers of the oils had been aEected somewhat more in the casea of the samples exposed in contact with tinplate, aluminum alloy 1&T, or stainless steel than for the remaining samples. The &ect of zinc and aluminum alloy 2SO was very
Figure 4.
The use of solution potential measurementa to predict whether cathodic protection (8, 14) can he successfully applied furnishes an example of another. type of laboratory test. If two dissimilar metals are coupled together and immersed in an electrolyte, in general, au electric current will flow between them. The metal from which positive current leaves to enter the electrolyte is the anode and the other metal is the cathode. Normally attack of the anodic metal is stimulated by such a contsct while attack of the cathodic metal is reduced. This reduction in attack of the cathodic metal caused by current flowing to it from the solution is termed cathodic protection. The mechanism of this protection has been discussed in previous papers (8,13). I n the classical electromotive series, aluminum is listed as having a more anodic solution potential than zinc. However, in many natural waters, including sea water, zinc is auodic to aluminum. Therefore, in such waters zinc attachments CBO be used to protect aluminum chemical equipment csthodically. Furthermore, it should be possible to determine under what conditions cathodic Drotection of
Effect of a Solvent-Refined Pennsylvania Lvbricatin Oil upon Metal Specimens Oxidized at 90' C. in Presence of ator
w9
Tind.1.
21°C
COPWI
AI~mImumalloy 14S-T
SIBinirr *el
LOW-rubo"
rt..l
INDUSTRIAL AND ENGINEERING CHEMISTRY
4 Table
V.
Potential Difference betweed Zinc and Aluminum in Various Solutions
Composition of Solution
pH
Temp.
Potential Difference
a "
Ti",,
r "I,
P .
6.5 7.5 8.5 9.0 9.8 10.7 11.2 3.7 2.6 1.6 6.0 10.8 3.4 5.6 10.7 2.8 6.4 6.9 7.3
Table
77 77 77 77 77 77 77 77 77 77 77 77 77 77 77 71 122 158 186 77
0 . 2 2 (Zinc anodic) 0 . 1 5 (Zinc anodic) 0 . 0 5 Zinc anodic) 0. 0 022 {Zinc [Zinc anodic) 0 . 1 6 (Aluminum anodic) (Alumjnum anodic) 0 . 3 7 (Aluminum 0 . 5 8 (Aluminum anodic) 0 . 3 0 (Zinc anodic) 0 . 3 1 (Zinc anodic) 0 . 2 8 (Zinc anodic) 0 . 3 2 (Zinc anodic) 0 . 2 3 (Aluminum anodic) 0 . 1 9 (Zinc anodic) 0 . 1 5 (Zinc anodic) 0 . 2 2 (Aluminum anodic) 0 . 0 5 (Zinc anodic) 0 . 1 8 (Zinc anodjc) 0.16 Zinc anodic) 0.16 !zinc anodic) 0 . 1 (Zinc anodic)
in predicting the feasibility of cathodic protection under service conditions. In addition to proper potential relationships, suitable spacing Jf zinc attachments is required in order for protection to be 100% effective. Location and distribution of the zinc attachments a& much more difficult to determine by Iaboratory tests. At present these points are generally determined by engineering judgment based on the analysis of the water, the potentials of zinc and aluminum, anll the construction of the part to be protected. SUMMARY
To predict the performance of metals under service conditions, laboratory test must give results that correlate directly with emice results, and conditions of service must be simulated as closely as possible. Attempts to accelerate the laboratory teat by intensifying one of the factors encountered in service often lead to misleading results. The development of a test of aircraft fuel tanks is described. Results'obtained from simple tests which neglected various
VI. Potential Difference between Zinc and Aluminum in Industrial Wahn
Composition of Water Total Temp. Source of Water pH CI 80, aolid. P.p.m. P.p.m. P.p.m. F. New Kensington. Pa., tap water 7 . 8 8 91 169 77 7.9 8 91 169 122 8.1 8 91 169 168 Memphis. Tenn.. well water 87 .. 22 .8. 91 .. leg 7.4 .. ; 7.8 .. 8.6 .. . 186 Xlanitowac, Wis.. tap water 8.4 14 90 318 77 8.6 14 BO 318 122 8.2 14 90 318 158 8.7 14 90 318 186 Kewauner, Wia.. tap water 8.0 84 261 667 77 8.1 34 261 687 122 7.8 34 261 687 I58 Altoona, Pa., synthetic tap water 44 .. 48 55 61 98 77 61 98 122 4.1 5 61 @8 158 4.3 6 61 98 185 Gowanus Canal, Brooklyn (under quwcent conditlons) 7.3 9,000 1,200 18.630 77 Gowanus Canal, Brooklyn (air bubbled through nolution) 7.3 9,000 1,200 18.5sO 77
..
..
:
Potential Difference Poll Zn anodic to AI 0 . 2 7 Zn anodic to AI 0 . 2 3 Zn anodic to AI 0 . 2 6
'E E: :$!:
..
Vol. 17, No. 1
:; E; t;$i; it:t ::g
Al anodic to Zn 0 . 0 1 Zn anodie to AI 0 . 5 3 Zn anodic to A I 0.40 A1 anodic to Zn 0 . 0 8 AlanodictoZn0.1 Zn anodic to AI 0.aO Znanodicto AI 0 . 4 1 AI anodic to Zn 0.08 Zn anodic anod/c to Zn to AI AI 0.60 0.40 Zn anodic to AI 0.M) Zn anodic to A1 0.46 Zn anodic to A1 Zn anodic to AI
0.29 '
0.26
service factora were inconclusive; it was necessary toduplicate the conditionsot service in order to obtain dependable results. In two testa the effect of the metal on ita environment was of more importance t h , the ~ c o d o n mktance of the itself. Copper was found to accelerate the decomposition of cracked fuels a t room temperature and the decomposition of a lubricating oil a t higher temperatures. Aluminum d o 5 and stainless steel were genedly inert in these tests. Other
metalaandalloyshadadefhiteeffectunder s ~ c s c conditions. Measurement of solution potentiala of zinc and aluminum has been found to be a useful .laboratory test for predicting the f&bility of using athodic protection for duminum chemical equipment. A correlation between service reeulta and potential measurements ia given.
ACKNOWLEDQMENTS this kind is feasible, by measuring the solution potentials of zinc and aluminum under conditions similar to those of service. The fuels wed in the studiea of the mutual effect of gasoline In Tables V and VI the potentials of zinc and aluminum in a and met& were mpplied through the courtesy of D. R. Stevens wide variety of natural waters and dilute salt solutions are given. of Mellon Institute, who also grrve advice and aasistance in conI n most cases, zinc is anodic to aluminum in nearly neutral or in ducting the teats. definitely acid solutions, but reverses in potential in alkaline E. M. Kipp of the Aluminum W r c h Lsboratoriea coopereolutions. Usually the potential difference is less favorable for ated in planning and conducting these tests. cathodic Drotection in hot solution than in cooler solutions. For the past 5 years, wherever the a p Table VII. Examples d Cathodic Protection of Aluminum by Zinc in Industry plication of cathodic protection to alumhum equipment was considered, the soluCompoaition of Coolins Potential Water Difference tion potentiala of zinc and aluminum have Service Application pH C1 804 solid. Total Tpmp. Znto Anodid AI PeriodRwulta Protection been measured in the particular solution P a m . P.p.m. P.p.m. O F. Vol: Yaarr or water in question at the service. temShell and f.ubecondenrer, 4 . 1 14 5 120 63 2 0.6 Complete perature and the decision aa to whether reclaimed rater t h r o q h tuba cathodic protection by zinc attachments Ammonra de hlegmator, 6 . 7 208 1,169 2,087 2 77 0.39 Partii was feasible. haa been based on these spray pontwater Ammonia de hlesmator, 6 . 7 20% 1,159 160 2 2.067 0.28 Partial meeeuremente. spray ontaater Heat excIanger AI t u b a 8 . 2 19 The resulta of measurements of solution 57 347 0 60 ... Partial c a s t iron shell a n d potentials and of behavior under d c e headers for coolinc gasen from Solvay conditions are given in Table VII. I t proccu with water Drinking water cooler, 7 . 8 8 91 will be noted that in all casea where zinc 169 40 0.25 3.5 Complete aluminum tobw was found to be definitely anodic to duJacketed tank for recrya- 7 . 3 9,000 1 3 0 0 18,630 0.29 2 77 Complete tallisms tartaric acid minwn, the use of zinc attachments under witb water aa coolant Condenser containing 7 . 2 .. service conditions haa been beneficial. ... 77 0.44 7 moa. Complete aluminum t u b a , steel Thus, the laboratory measurement of solu.bell. and well water tion potentiala has proved highly effective
ANALYTICAL EDITION
January, 1945 LITERATURE CITED
Am. SOC. Testing Materials, Method D155-39T. I b i d . , Method D157-36. Ibid.,Method D445-42T. Ibid., Method D663-42T. A m . SOC.Testing Materials Proc., 43, 275 (1943). Am. SOC.Testing Materials, "Standards on Petroleum Products", 1940. Borgmann, C. W., and Mears, R. B., "Principles of Corrosion
Testing", A.S.T.M. Symposium on Corrosion Testing Procedure, 1937. Brown, R. H., and Mears, R. B., Trans. Electrochem. SOC.,81, 465-83 (1942).
Dix, E. H., Jr., and Mears, R. B . , S . A . E . J o u r d , 4 6 , 2 1 5(1940).
5
(10) Hunter, B. F., Ambrose. H. .I..and Powers. K. P..Poiuer. 83. 97-9 (1939). (11) Mardles, E. W. J., Proc. World Petroleum Congress. 2,59 (1933). (12) Mears, R. B., Belt Lab. Record, 11, 141 (1933). (13) Mears. R. B., and Brown, R. H., Trans. Electrochem. Soc., 74, 519 (1938). (14) Mears, R. B . , and Fahrney, H. J.. Trans.A m . Inst. C h m . Engra., 37, 911 (1941). (15) Story, L. G., Provine, R. W., and Bennett, H. T., IND. ENG. CHEM.,21, 1079 (1929). PREBEATED before the Division of Petroleum Chemistry, Sympoaium on Bench Scale Techniques, a t the 108th Meeting of the A U ~ R I C ACNE I ~ M I C A L SOCIETY.New York, N. Y.
Ternary Mixtures of' Three Isomeric Heptanes
A
Quantitative M e t h o d of Analysis
VERLE A. MILLER, Research Laboratories Division, This paper describes a method based on a refinement of the solution temperpture of the hydrocarbon mixture in diethyl phthalate and nitrobenzene, b y which the composition of a mixture containing P,4- and P,%dimethylpentane with 4,4,3-trimethyIbutane may be determined quantitatively, the first two components within 396 and The entire analysis requires the last component within 0.3%. approximately one hour.
F
RrlCTIONAI, distillation, supplemented with curves for other pertinent physical data, is entirely suitable for the analysis of paraffin mixtures up to and including the hexanes, but these methods alone are not adequate for the analysis of certain mixtures of the heptanes (see Table I). Attempts have been made by a great many workers, in several fields of research, to develop adequate methods of hydrocarbon analysis. These include ultraviolet and infrared abeorption spectra (3, 19, 2.2, 24, 15) and Raman spectra (9, 14, 15, $8, sa), and more recently the mass spectrograph has been applied to the solution of i;hi3 problem. Rosenbaum, Grosse, and Jacobson (26) in their work on the Raman spectra of the nine isomeric heptanes, report that analysis of close to 50-50 binary mixtures gave results within 5%. However, an attempted analysis of t b ternary mixture of 2,4- and 2,2-dimethylpent,ane with 2,2,3triwt:thyibutne (the heptane mixture which boils a t about 80" C,;,?even in approximately equal proportions, gave results whirh varied as much as 120/,. This paper describes a method, based on a refinement of the solutios temperature of the hydrocarbon mixture in diethyl phthalate and nitrobenzene, by which the composition of a mixture containing 2,4- and 2,2-dimethylpentane with 2,2,3trimethylbutane may be determined quantitatively, the first two components within 3% and the last component within 0.37,. IC order to analyze such a ternary mixture quantitatively, it is only necessary to determine the solution temperature of the unknown sample in diethyl phthalate and nitrobenzene with en accuracy of ==O.0loC. These temperatures are then used with a series of calibration curves, which were prepared with mixtures of known composition, to determine graphically the percentage of each of the three constituents present in the unknown mixture. The entire analysis requires approximately one hour. HETORY OF APPLICATION OF CRITICAL SOLUTION TEMPERATURE MEASUREMENTS TO HYDROCARBON ANALYSlS
Chavanne and Simon (6) first observed that the presence of aromatic hydrocarbons decreased the critical solution tempera-
General Motors Corporation, Detroit, Mich.
ture of a hydrocarbon mixture in aniline and that the lowering was directly proportional to the weight of aromatics present. Tizard and Marshall (31) introduced the more simple determination of "aniline points", which numerous workers (2, 4, 13, 17, 18, 21, 23) have shown to be of the greatest utility for the determination of the quantity of the various classes of compounds present in gasoline and kerosene distillates. I t has been common practice to employ pure, dry aniline that will give an aniline point of 70" * 0.1" C. for n-heptane and a reproducibility of about 0.1" C. is usually claimed. As compared with freshly distilled aniline, water-saturated aniline may cause a rise of as much as 20" C. in the observed aniline point. Tilitsheyew and Dumskaya (29) studied the method for mixtures of pure aromatic hydrocarbons and mixtures of pure aromatic hydrocarbons with light petroleum distillates. .4ubree (1) used a second solvent, benzyl alcohol, and thus obtained two equations with two unknowns which he could solve for the aromatic content without removal of these hydrocarbons by chemical means. Erskine (12) first used nitrobenzene instead of aniline for the determination of aromatics and'reported that this critical solution temperature decreased with rise in molecular weight instead ot increasing as with aniline. Considerable work on the critical solution temperature of various pure hydrocarbons in one or more of the three solvents, aniline, benzyl alcohol, or nitrobenzene has been done by Chavanne and Simon ( 6 ) , Garner (13), Maman (,El),Edgar and Calingaert (fO),and Wibaut, Hoog, and Smittenberg (33). As far as the author has been able to determine there is no mention in the literature of any attempt to use this valuable and easily determined constant for the quantitative determination of individual paraffin compounds which are present in a mixture, SEARCH FOR OTHER CRITICAL SOLUTION TEMPERATURE SOLVENTS
A preliminary study showed that the spread between the aniline points of pure 2,4- and 2;2-dimethylpentane is only 0.35' C. This agrees well with the value (0.4') obtained by Wibaut, Hoog, and Smittenberg (33) but not with that (1.1") obtained by Edgar and Calingaert (10) (see Table I). In all, 97 compounds were investigated in an attempt to find solvents which would give a wider spread of solution temperetures for these two hydrocarbons. The criteria for such a solvent are: It must be obtainable in a pure state; it should be fairly stable; it must give a solution temperature within a reasonable working range; and it mi=- give a satisfactory end point with B
