V O L U M E 23, NO. 4, A P R I L 1 9 5 1
663
ever, because slower wave drive speeds may be used, or in the extreme cases, point to point settings of the wave-length selector may be employed a t such points, and sufficient time allowed for the recorder to come to an equilibrium position. The authors' method simply reveals the slowness in response in regions of rapidly changing optical density, which is a characteristic of the instrument and would be a source of error in any method of correction for radiation change. For qualitative analysis of spectra, the nomograph is used to permit the tracings of sample and radiation spectral densities a t identical slit widths and different gain settings, the spectral density at either gain setting is converted to its value a t the other by use of the nomograph, and optical density is determined as the difference of the two spectral densities calculated a t the same gain setting.
is apparent, showing that this method of calculation is essentially independent of slit width. The difference between these densities and those by the baseline method is essentially the difference between the radiation blank and the base line. I n the region 1300 t o 1600 cm.-l, direct comparison to the blank wm not possible, nor was the baFe line a t the wider slit widt,h necessary so easy to construct. The effect on the optical density calculated from blanks a t gains widely different from those used for the sample is illustrated in Figure 3. The differences observed are probably due to changes in resolving power with changes in slit width, as evidenced by a slight loss in fine structure in calculating through two changes in gain setting, but there is no significant difference in the general shape of the curves. LITERATURE CITED (1) Freed, XI., Brenner, 148 (1949).
COMPARISON OF OPTICAL DENSITY
Determination of optical density by several different methods
S.,and
Wodicka,
V. O., Food Technol., 3,
is shown in Figure 2. I n the region 1600 to 2000 em.-' it was
(2) Heigl, J. J., Bell, IT.F..and White, .J. C., ASAL. CHEM.,19, 293 (1947).
possible to determine the optical density of the sample by direct comparison with a radiation blank, by the baseline method, and I)? comparison with a blank one gain setting lower than that used for the sample. The agreement between the densities calculated fur the first and third methods, obtained at different slit widths,
RECEIVED May 18, 1950. This paper reports research by the Quartermaster Food and Container Institute for the Armed Forces, and has been assigned number 308 in the series of papers approved for publication. The views or ronclusions contained in this report are those of the authors. They are not to be construed as necessarily reflecting the views or endorsement of the Derrartment of the Army.
Analysis of Three-Component liquid Mixtures by Refractive Index Alone WILLIAM M . SPICER AND LEON H. .MEYER' Georgia Institute of Technology, Atlanta, Ga.
CCORDING to the phase rule, a three-component system in a single phase has, a t constant temperature and pressure, two degrees of freedom. Such systems are commonly analyzed by the determination of two physical properties; typical examples are found in the work of Honold and R'akeman (1) and Plein and Poe (6). It wexm that the determination of a single property a t two different temperatures would be equivalent to the determination of two different properties a t a single temperature.
T a h l e I . Refractive Indexes a n d T e m p e r a t u r e Coefficients Component Kater (9) Acetone (3) n-Butyl alcohol (4) 1.4-Dioxane (6) 13xprrimentally determined.
n, 200
c.
1 33300 1.35931 1.39909 1 4221
An At
0.0001 0.00075 0.0004
0.0004a
MOLE FRACTION H,O Figure 1 I n order to test this proposition it was decided to use as the physical property the index of refraction, because it is not only easy to memure but also sensitive to changes in temperature. It was believed that, although for a system of three components there are an infinite number of compositions corresponding to a given index, the index of each of these would change a t a different rate with respect to the temperature. I t was hoped that this difference in rate of change of index with temperature would make possible m analysis of the solution. The most favorable systems to use are those in which the three components have indexes that are widely different and have very different temperature coefficients. Two systems were used : ( I ) water-acetone-n-butyl alcohol and (11) water-acetone-1,4dioxane. The indexes and temperature coefficients are shown in Table I. The low miscibility of n-butyl alcohol with water limited the 1 Present address, Department of Chemistry, Universlty of Illmais Urbana 111.
single-phase range in the system water-acetone-n-butyl However, the range was sufficient for the purpose.
alcohol.
EQUIPMENT
The refractometer used was a Bausch & Lomb precision refractometer whose range is 1.20to 1.51. With this instrument indexes can be obtained to six significant figures. The temperature was controlled b y means of a Precision Scientific Co. constant temperature bath, which is Baid to control the temperature to +0.03" C. The thermometer used in the refractometer was calibrated in 0.1" C. On it no temperature variation was observed. EXPERIMEYTAL PROCEDURE
The preparation of the reference solutions was laborious, because they were made to have predetermined mole fractions of the three components. Although only several drops of solution were needed for a determination, approximately 20 ml. were made in order to minimize the effect of evaporation. The desired
ANALYTICAL CHEMISTRY
664 amount of each component was weighed accurately in a weighing bottle and the three components were mixed. T h e indexes were then determined at two temperatures. These temperatures should be as far apart as possible; however, the up er temperature is limited by the evaporation of the sample a n t t h e lower is limited b y the condensation of water vapor from the air into the sample. RESULTS
T h e results are shown in Tables I1 and 111. From the data, plots of the form shown in Figures 1 and 2 were constructed of
X
1356
z W
2 1348 t-
refractive indes us. mole fraction water, yielding two families of curves-one for constant mole fraction of acetone, the other for constant mole fraction of n-butyl alcohol (or 1,4-dioxane). In order to test the method, solutions were made of arbitrary but known composition lying near the mid-portion of the graphs. The refract,ive indeses of these were then measured a t the two temperatures. The possihlc solutions, of various concentrations, rshibiting these indeses of refr:ic36 9 5
-
System Mole fraction water Mole fraction acetone hlole fraction n-butyl alcohol
n$’
0.34032 0.33944 0.33991 0,33951
0.36000
0.35982 0.35984 0.35991 0.37980 0,38034 0.38014 0.37981 0.39976 0.39987 0.39989 0 39997
Experimental Determinations
Actual Composition
0.00
Refractive Indexes
Weight Fraction Acetone 1,4-Dioxane
J
hIeasiired Composition
Water-Acetone-n-Butyl Alcohol 0 90943 Nole fraction water 0.06960 Mole fraction acetone Mole fraction n-butyl o.02007 alcohol
System Water-Acetone-1,4-Diolane Wt. fraction water 0.59769 Wt. fraction water 0.03.562 Wt. fraction acetone K t . fraction acetone Wt. fraction l,.Gdioxane TTt. fraction 1,4-dioxane 0 36660 0.58979 W t . fraction water FTt, fraction water Wt. fraction acetone 0.08050 T5-t. fraction acetone Wt. fraction 1,4-dioxane Wt. fraction 1,4-dioxane 0.37971
0 90923 0 06937
n0 ~ 1 ~ 0 0.59923 0.03530 0.36545
0,58230 0.04880 0 36890
1.33913 1,34289
1.34535 1.34762 1.34259 1,34535 1.34802 1.35017 1.34551 1.34790 1.35052 1.36277 1.34789 1.35005 1,36226 1,35406 1.34973 1.35184 1,35384 1,35520
LITERATURE CITED
(1) H o n o l d , E., a n d W a k e m a n , H., ISD. ENG.CHEM.,ANAL.ED..16, 499 (1944).
( 2 ) “ L a n d o l t - B o r n s t e i n Physikalisch-Chemische T a b e l l e n , ” Yol. 11, p . 956, Berlin, J u l i u s Springer. 1923. (3) Ibid.. p. 971. (4) Ibid., p. 975. (5) L a n g e , K. A , , “ H a n d b o o k of C h e m i s t r y , ” 6 t h ed.. p. 923, Rand u s k y , Ohio, H a n d b o o k Publishers. 1946. END.CHERI., Ax.4~.ED..16, 168 (6) Plein, E. Lf,,and!Poe,:C. E.. IND. (1944). RECEIVED September 1, 1950.
