406
TROY A. SCOTT, JR.
It is recognized that lubricating oil which has been subjected to different heat treatments is too variable in composition and too little understood to be a good material for an initial study. More than one solid surface should also be iised in the investigation. These and other refinements will be the subjects of future investigations. SUMM.4RY
A direct experimental method of estimating tthe re1ntii.e tendencies of different oils to spread on a polished steel surface is described. Representative values for lubricat'ing oils in different degrees of oxidation are given and compared with the tendencies of tlic same oils to spread on water. REFEREXCES J HARKINS, D., A N D FELDBIAN, h.:J . A m . Chem. 80c. 44, 2GG5 (1822). KEIM,CHRISP., A N D WASHBURN, E. R O ~ E RJ .: Am. Chem. SOC.62, 2318 (1040), LANGMUIR, IRVING: J. 241n.Chem. 8oc. 39, 1818 (1917). SHANKLIN, G. B., A X O MACICAY,G . IZI. J.: Trans. Am. Inst. Elect. Engrs. 48, 364 (1929). ( 5 ) TRANSUE, L A U R E N C E F., WASHBURS, E. ROGER, . \ N D I C A H L E R . FLOYD H.: J. Am. Chem. SOC.64, 274 (1012). (6) WASHBURN, E. ROGER, A N D KEXM, CHRISP.: J . Ani. Chcm. SOC.62, 1747 (1940). (7) WASHBURN,E. ROGER,' r R A N S U E , LAUREXCE F., A N D THOMPSON, THEOS J . : J . Am. Chem. SOC. 63, 2742 (1911). (1) (2) (3) (4)
w.
REFRACTIVE INDEX OF ETHAIC'OL-WATER MIXTURES A4ND DENSITY AND REFRACTIVE INDEX OF ETHANOL-WATERETHYL ETHER iMIXTURES D
TROY A . SCOTT, JR. Northerii Regional Research Laboratory,' Peoria, Illiuois Received A p r i l 23, 1946
The measurement of the refractive indes of a misture of ethanol and water provides a simple, rapid determination of the composition. However, values found in the literature for the refractive indices of various concentrations of alcohol-water mixtures are not in good agreement. Leach and Lythgoe (3) gave their results only in terms of Zeiss degrees for the dipping refractometer, and did not indicate their procedure for preparing the misture. Andrew (1) reported only the indices for the range 70-100 per cent alcohol. Elsey and Lynn (2) gave results covering only the compositions 0-28.43 per cent alcohol. Oelke and Arnold (4) reported values for the refractive index to the fourth decimal only and gave nzE = 1.3327 for water, whereas Tilton and Taylor ( 5 ) report 1 One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. e. Department of Agriculturc.
REFRACTIVE INDEX O F ETHAKOL-WATER
nF
407
MIXTURES
= 1.3325026. Table 1 compares the indices a t various concentrations as
reported by four different investigators. I n the present work no attempt was made to prepare completely anhydrous alcohol, since many of the usual methods of doing so introduce impurities. Instead, a nearly anhydrous product was obtained by fractional distillation of commercial absolute alcohol through a 4-ft. Podbielniak column. The first 10 TABLE 1 Comparison o j values of refractiw index of ethanol-water niixtures at 25°C. obtained by several inccstioators PER C E N T ALCOEOL
0 20 80 100
Andrews
Elsey and Lynn
1.33251 1.34604t 1.36331 1.35941
I.C.T.*
Oelke and Arnold
1.3331
1.3327
1.3599
1.3595
Scott
1.33252 1.34600 1.36290 1.35912$
* Source of these values unknown. They do not appear in thc reference given in Tnternalional Critical Tnbles, Vol. VII, p. 67. t Interpolated. $ Estrapolatcd. TABLE 2 Optical d e n s i t y of alcohcl used in this investigation WAVE LENGTH
DENSITY OF 1 CM.
3100 3000 2900 2800 2700 2600 2500 2400 2300 2250 2200 2150 2100
0.0023 0,0028 0.0040 0.005O 0.0090 0.0178 0.0295 0,0580 0.120 0.174 0.244 0.330 0.482
per cent of distillate contained all the residual benzene left from the commercial azeotropic dehydration of dcohcl. The next 80 per cent of distillate was satisfactory for use in the index measurements. Ethyl alcohol prepared in this way was examined spectrophotometrically. The data nre shown in table 2. Analysis by the Karl Fischer method shoved 0.22 per cevt lvater present. The density i t 2 vacuo a t 25°C. was 0.78583, corresponding to a composition of 99.75 per cenl ethanol and 0.25 per cent water. As a further check on the purity of thc ethanol, commercial 95 per cent alcohol byas diied vith calcium oxide, and then distilled through the Podbielnialr column. Karl Fischer analysis showed
408
TROY A. SCOTT, JR.
1.40 per cent mater present, compared to 1.42 per cent water found by density measurement. When the refractive index of this ethanol was plotted against Densit 25°C. (in oacuo)
DENSITY AT
0.78590 0.78650 0.78833 0,78943 0.78979 0.79076 0.79187 0.79259 0.79440 0.79640 0.79690 0.80018 0.80476 0.80690 0.81298 0.81405 0.81846 0.81879 0.82259 0.82271 0.82661 0.82711 0.82806 0.83096 0.83516 0.83T09 0.83770 0.83962 0.84195 0.84406 0.84564 0.84705 0.84788 0.84991 0.85325 0.85462 0.85987 0.86139 0.86629
TABLE 3 composition, and ~ e f ~ a c t i ivned e x of mixtures of ethanol and water WEIGHT PER CEN: WATER'
0.27 0.47 1.06 1.43 1.54 1.86 2.24 2.48 3.09 3.77 3.94 5.10 6.74 7.51 9.76 10.17 11.84 11.97 13.43 13.48 15.00 15.20 15.58 16.73 18.53 19.1s 19.43 20.21 21.15 22.38 22.66 23.24 23.37 24.41 25.79 26.36 28.53 29.16 31.21
$0
D
1.35923 1.35926 1.35958 1.35967 1.35970 1.35996 1.36005 1.36011 1.36037 1.36049 1.36065 1.36093 1.36134 1.36156 1.36188 1.36200 1.36226 1.36220 1.36238 1.36245 1.36260 1.36260 1.36267 1.36276 1.36252 1.30259 1.36289 1.36202 1.36205 1.36292 1.36298 1.36289 1.36202 1.36292 1.36289 1.36289 1.36276 1.36270 1.36257
25°C ( i n oacuo)
DENSITY AT
0.86725 0.87154 0.87395 0.88220 0.88217 0.88900 0.89616 0.90186 0.90438 0.91185 0.91397 0.92310 0.92604 0.92834 0.93350 0.94098 0.94461 0.94962 0.94054 0.95150 0.95540 0.05874 0.96081 0.96208 0.06510 0.96515 0.96688 0.06942 0.07437 0.97976 0.95131 0.98108 0.98585 0.98850 0.98846 0.99327 0.09547 0.99657 0.99708
WEIGHT PER C E N WATER'
31.61 33.42 34.44 37.87 37.93 40.87 43.98 46.47 47.58 50.90 51.86 56.04 57.41 58.50 61.03 64.75 66.66 69.41 69.36 70.48 72.78 74.87 76.21 77.06 79.17 79.14 80.34 82.14 85.75 89.54 90.61 01.03 93.54 95.20 95.17 97.95 99.14 99.73 100.00
?go 1.36251 1.36235 1.36226 1.36178 1.36178 1.36125 1.315074 1.36027 1.3ti002 1.35023 1.35893 1,35780 1.35736 1.35602 1.35610 1.35462 1.35374 1.35248 1.35248 1.35187 1.35057 1.34935 1.34552 1.34798 1.33657 1.34600 1.34590 1.31455 1.31199 1.33936 1.33855 1,33825 1.33655 1.33549 1.33546 1,33374 1.33300 1.33205 1.33252
* Calculated from the density. weight per cent composition, it fell upon the curve obtained for the ethanol prepared from commercial absolute alcohol. The distilled water used had a specific conductance of about 2 X lo-' ohm-' cm.-'
409
REFRACTIVE INDEX O F ETHANOL-W.4TER MIXTURES
The refractive indices were measured with a Dausch and Lomb precision refractometer, the temperature being controlled to &O.O5"C. Density measurements were made with a 25-ml. pycnometer, calibrated with freshly boiled distilled water. The pycnometer was immersed in a large water bath maintained at 25°C. f 0.03". TABLE 4 for integral percentage composition of ethanol-water inislures
Interpolated values for n:' WEIGBT PER CENT WATER
0 1 2 3 4 5
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
figo
1.35912* 1.35952 1,35991 1.36030 1.36063 1,36092 1.36118 1.36141 1,36162 1,36181 1.36198 1.36213 1.36226 1.36239 1,36251 1.36261 1.36269 1.36276 1.362S2 1,36287 1.36200 1,36203 1.36204 1.36294 1.36203
___
1
WEIGHT PER CENT WATER
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
, I/
49
?go 1.36290 1.36287 1.36283 1.36278 1.36272 1.36265 1.36257 1.36248 1.36238 1.36227 1.36216 1.36204 1.36191 1.36177 1,36162 1.36146 1.36130 1.36113 1.36004 1.36078 1.36055 1.36035 1.36014 1.35902
1
50
1
/I II
WEIGHT PER CENT WATER
51 52 53 54 55 56 57 58 59 GO 61 62 63 64 65 66 G7 68 69 70 71 72 73
Vg'
1.35946 1.35921 1.35895 1.35867 1.35839 I.35810 1.35780 1.35749 J .35716 1,35683 1.35647 1.35612 1.35573 1* 35534 I . 35403 1.35451 1.35407 I.35361 1.35314 1,35264 1. 35213 1.35160 1.35104 1.35047 1.34089
WEIGHT PER CENT WATER
75 76 77 78 79 80 81 82 83 84 85 SO 87 S8 89 00 91 02 03 04 05 90 97 95 99 I00
.254
D
1.34927 1.34864 1.34800 1* 34734 1.34668 1.34600 1.34531 1.34463 1.34304 1.34323 1.34251 1.34180 1.3UOO 1.34039 1.33969 1.33599 1.33830 1.33762 1.33604 1.3362fi 1.33560) 1.33405> 1.33432: I . 33371 1.3331 1 1.33282
* Ex! mpolatecl. Mistures ranging in composition from 99.7 per cent alcohol to 100 per cent water were prepared, boiled, and the densities and indices measured. Using a density-composition table compiled by the Bureau of Standards (Circular of the Bureau of Standards, No. 19), the water content of the mixture was computed (table 3). To obtain an equation for the composition-indes curve, the indices were converted t o t'he Lorenx-Lorentx specific refraction:
410
TROY .4. SCOTT, JR.
When 1' was plotted against jn (mole fraction of ivater in the misture), a curve was obtained which closely it?sernbled an hyperhola of the type -
+ 6ni + c ?)1
a
So as to fit the deri\-ed curve more closely to the data, the range of composition was broken up into nine overlapping sections, and the constants for each section iveie calculated by the method of least squares. The equation was then Iwonverted into terms oi indes, density, and weight per cent water, and the refractive indices were computed for integral values of per cent water (table 4). Thc composition of a mixture of ethanol, water, and ethyl ether can be conveniently deteimined by use of density and refractive-index data. To do this, it is necessary to make up accurately solutions covering that portion of the system which is of interest, and to find the densities and indices of the prepared solutions. Then the compositions may Le plotted on triangular coordinate paper, and lines of equal density and of equal refractive indes drawn. Mixtures of the three components were prepared ranging in composition from 90 per cent ethanol, 6 per cent ether, 5 per cent water to 100 per cent ethanol. The ethanol and water used were the same as described in the first portion of this paper. Merck's absolute, i,eagent-grade ether was used after treatment with dilute potassium permanganate solution and distillation through a 4-ft. Podbielniak column. Thc ether vas then nnalyzed for water content with the Karl Fischer reagent, : ~ n dthe amountJ of ivater found was included when calculating the composition of each misture prepared. The values of density and refractive indes found for the prepared mistures are given in table 5 . From the data given in table 5, lines of equal density and of equal indes were constructed, and were found to be Yery nearly straight. However, the slope of the equal index lines ivas not greatly different from that of the lines of equal density, so that an eiwr of six units in the fifth decimal place of the refractive indes amounted to an error of about 1 per cent of the ethanol content. A much more accurate analysis of this three-component system was found to lie in the use of the Karl Fischer reagent. The water content of the etherethanol-water niisture can be determined by the Karl Fischer method, and, after measuring the density, thc amounts of ether and ethanol present can be found by interpolation from the equal-density lines. RUMMART
Varying amount,s of distilled water were added to samples of pure ethanol prepared by fractional distillation. The density and index at, 25°C. of each of these mixtures were measured, and the composition of each .\vas calculated from thc density in V O C U O . These experimental data w1.e fitted to an equation, and the refractive indices ~vcrccomputed for integral values of weight per cent water. 3Iistnres were prepared of a ternary system varying in composition from 90 per cent ethanol, 5 per cent water, 5 per cent ethyl ether to 100 per cent ethanol. The density and index at. 25°C. of each of these mixtures were measured and recoi-ded in n table. From t,his table, lines of equal density and of equal index
REFRACTIVE ISDEX OF ETHANOL-WATER MIXTURES
411
TABLE 5 Density and refraclive i n d e x of ether-elhanol-iualer mixlures at 36°C.
?go
WFXGHT FER CENT WATER
WEIGET PER CEN'I ETEER
WEIGHT PER CENT ETEANOL
DENSITY IN AIR
CENSITY in vacuo
0.32 0.33 0.33 0.34 0.35 0.35
0.00 1.01 2.01 2.91 4.01 4.87
09.68 08. 66 07.66 96.75 95.64 04.78
0.78496 0.78437 0.78380 0.78323 0.78260 0.78205
0.78604 0.78546 0.78489 0.78432 0.78368 0.78314
1.33 1.33 1.33 1.32 1.32 1-31
0.00 1.04 1.95 3.03 4.07 5.08
98.67 97.63 96.72 95.65 94.61 93.61
0.78806 0.78744 0,78684 0.78613 0.78548 0.78483
0.78915 0.78853 0.78793 0.78722 0.78657 0.78592
2.28 2.27 2.25 1.98 1.96 2.21
0.00 0.95 2.13 2.90 3.9s 5.08
97.72 96.78 95.62 95.12 94.05 92.71
0.79091 0.79029 0.78949 0.78824 0.78752 0.78755
0.79200 0.79138 0.79058 0.78932 0.78860 0.78864
2.27 2.25 2.20 2.16
0.00 1.00 3.01 4.97
97.73 96.75 94.79 92.87
0.79088 0.79020 0.78879 0.78742
0.79197 0.79129 0.78988 0.78851
1.36002 1.36004 1.36000 1.35988
3.22 3.19 3.16 3.10 3.07
0.00 1.03 2.12 3.02 3.90 4.95
06.78 95.78 94.72 93.85 93.00 91.98
0.79371 0.79300 0.79216 0.79154 0.79091 0.79011
0.79480 0.79409 0.79324 0.79263 0.79200 0.79120
1.36038 1.36038 1.36034 1.36032 1.36027 1.36027
4.15 4.11 4.07 4.03 3.99 3.96
0.00 1.10 2.05 3.07 3.96 4.96
95.85 94.79 93.88 92.90 92.05 91.07
0.79641 0.79566 0.79494 0.79421 0.79352 0.70279
0 * 79749 0.79674 0.79603 0.79530 0.79460 0.79387
1.36068 1.36062 1.36065 1.36060 1.36060 1.36056
5.50 5.44 5.39 5.34 5.29 5.23
0.00 1.05 2.05 2.95 3.90 5.00
94.50 93.51 92.56 91.71 90.82 89.77
0. SO022 0.79941 0.79862 0.79703 0.79717 0.79626
0.80130 0. SO050 0.79971 0.79901 0.79826 0.79735
1.36105 1.36102 1.36100 1.36096 1.36096 1.36093
3.13
1.36926 1.35922 1.35924 1.35923 1.35920 1.35923
may be drawn upon triangu1a.r coordinate paper, and, by use of the diagram, compositions of mixtures within the stated limits may be determined. How-
41 2
H. L. CUPPLES
ever, a more accurate analysis consists in the determination of water content by the Karl Fischer method. The amounts of ether and alcohol in the mixture can then be found by measuring the density of the mixture and employing the diagram of equal-density lines. REFERENCES
(1) ANDREW, L. W.: J. Am. Chem. SOC.30, 353 (1908). (2) ELSEY,H. ILL., A N D L Y N NG. , L.: J. Phys. Chem. 27, 342 (1923). (3) LEACH,A. E., A N D LYTHGOE, H. C.: J. Am. Chein. SOC.27. 964 (1905). (4) OELKE,W. C., AND ARNOLD,R.: Proc. Iowi Acad. Sci. 43, 175 (1936). ( 5 ) TILTON, L. W., A K D TAYLOR, J. IC.: J. Research Sstl. Bur. Standards 20, 419 (1938)
T H E SURFACE TEKSION OF CHLOROFORM: ITS VARIATION WITH T H E COMPOSITION OF T H E GAS PHASE H. L. CUPPLES Burcau of Entomology a w l Plant Quarantine, .lgrictLlturul Research Administrution, U.S . Department of A g r i c u l l w c , Rsltsiu’llc, i l I u r ~ l a n d
Rccciccd A p i l 8, 1946
Although the surface tension of chloroform has been determined by a number of independent investigators, a critical examination of their results discloses a remarkable lack of concordance. This is particularly surprising in view of the fact that chloroform is a very well known and readily available chemical compound. Schiff’ (12) used the method of differential capillary rise, the capillaries being filled with the liquid while immersed in the vapor of the boiling liquid. He found 7 8 0 = 28.71 dynes per centimeter and 760.60 = 21.73 dynes per centimeter. Ramsay and Aston (8) used the method of capillary rise, the capillary being enclosed in a glass tube from which the air was displaced by boiling the liquid. They found the values given in table 1. Whatmough (16) used the method of maximum bubble pressure. His value for the surface tension of chloroform, recalculated on the assumption that for ether 7180 = 17.30 dynes per centimeter, is y l ~ o = 27.08 dynes per centimeter. Morgan and Thomssen (7) measured the drop-weights of chloroform a t two temperatures. They were interested primarily in measuring the degree of association of liquids and did not calculate the surface tensions. Harkins and coworkers (4) employed the drop-weight method and found y200 = 27.13 dynes per centimeter. Richards and Carver (lo), employing the method of capillary rise, found 7 2 ~ 0(in vacuo) = 27.24 dynes per centimeter and 7 2 6 O (in air) = 27.14 dynes per centimeter. Hennaut-Roland and Lek ( 5 ) used the method of capillary rise. They found 7160 = 28.06 dynes per centimeter, y z O D = 27.28 dynes per centimeter, and yaoo = 25.89 dynes per centimeter. Akhmatov (3) measured the differential
