1911
V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6
point of titanium tetrachloride under saturation pressure n-ith zero impurity, Tjo, was calculated t o be -24.10" & 0.01" C. Figure 6 shows curves of experiments done under saturation pressure. The curve in Figure 7 was obtained ivith the sample under 1 atm. of dry nitrogen. I n other experiments, not shown in the figures, the temperatures of the freezing curve of a sample of titanium tetrachloride a t saturation pressure were observed to be 0.007" C. lower than the corresponding temperatures of the freezing curve of the same sample under a pressure of 1 atm. of nitrogen.
LL
c,
+
23042
1-
titanium tetrachloride purity 99 9 3 ma!e %
'L (r,
w
23 0 4 0 -
LITERATURE CITED I IO
20
35
40
50
60
1-1 70
T I M E IN M I K L T E S
Figure 7.
Freezing curve of titanium tetrachloride under 1 atm. of dry nitrogen
(1) Glasgow, A. R., Jr., Krouskop, S . C., Beadle, Joan, hsilrod. G. D., Rossini, F. C., ASAL. CHEX 20, 410 (1948). (2) Glasgow, 8.R., Jr., Krouskop, S . C., Rossini, F. D., I b i d , 22, 1521 (1950). (3) Glasgow, A. R., Jr., Ross, G. S., J . Research SatZ. Bur. Standards 5 6 , 137 (1956).
(4)
Grale of ordinates gives resistance in ohms of platinum resistance ttiermometer (0.1 o h m is approximately 1.0' C.).
(1945). ( 5 ) lIair, B. J., Glasgow, A. R., Jr., Rossini, F. D., Ibid., 26, 591 (1941). (6) Schwab, F. W., Wichers, E., "Temperature, Its IIeasurement and Control in Science and Industry," pp. 256-G4, Reinhold, S e w I'ork, 1941. ( 7 ) Taylor, W.J., Rossini, F. D., J . Reseaich S a t l . Bzar. Standards 32, ,197 (1944).
EXPERIMESTAL DATA
The procedures for determining the purity from time-temperatiire freezing and melting curves and the principles involved are given in earlier publications ( I , 8,4-7). Three typical freezing point curves obtained with titanium tetrachloride samples of different levels of purity was shown in Figures 6 and 7 . From a series of experiments such as these a value for the freezing
Glasgow, -1.R., Jr., Streiff, A. J., Rossini, F. D., Ibid., 35, 353
RECEIVED for review M a y 3, 1966. Accepted August 30, 1 9 X . Division of Analytical Chemistry, 128th Meeting, ACS, Minneapolis, Blinn., September 1955. Work partially supported b y the Edgewood h r m y Chemical Center.
Factors Affecting Use of Dielectric Methods in Determination of Sea Water in Navy Special Fuel Oil T. D. CALLINAN, R. M. ROE, and J. B. ROMANS U. S. N a v a l Research Laboratory, Washington 25, D. C. The dielectric constant, per cent power factor, dielectric loss factor, and conductivity of a number of boiler fuels were evaluated as a means of measuring the sea w-ater content of Navy Special fuel oils on shipboard. These properties varied considerably from one fuel oil to another at comparable frequencies from 10 kc. to i 5 RIc. When these oils were emulsified with synthetic sea water, the values so obtained increased with increasing sea water content but remained a function of the characteristics of the original fuel oil. The necessity of using a dry reference sample is emphasized.
I
Ii T H E course of investigating the causes of fuel slagging in
Xavy boilers, it became increasingly evident that information concerning the degree of contamination of Navy Special fuel oil by sea water nould be of considerable value. Present analytical methods, n-hile highly accurate, are timeconsuming and of little assistance under actual operational conditions. It would be desirable, therefore, to have a compact and rugged instrument that would indicate, or record continuouslj variations in the salt water content of Navy Special boiler fuel. S o suitable instruments or devices are available a t the present time, although several methods have been proposed for the determination of sea viater in fuel oil, each based on the measurement of some m-ell-establishedelectrical property of hydrocarbons or of water ( I O ) . Among several methods proposed n-ere those for the determination of salt water content of emulsions by ( a ) determination of the dielcctric constant of the emulsion or
the change in dielectric constant as a function of salt water content, ( b ) change in per cent power factor, ( c ) change in dielectric loss factor, and ( d ) change in conductivity. Although dielectric constant measurements have been used to follow the progress of oxidation in petroleum products, to determine impurities in transformer oils, for the detection of m-ater in hydrocarbons, and the like ( l e ) ,such determinations are made on highly refined, essentially nonpolar materials. The impurity usually represents only a trace or a t least a very minor constituent of the product under examination. In contrast, boiler fuel oils, including Navy Special fuel oils, are complex mixtures of variable composition, chiefly hydrocarbon in nature, containing appreciable amounts of polar compounds. I n addition to aromatic and paraffinic compounds knonm to be present, S a v y Special fuel oil contains large amounts of asphaltic and resinous materials of unknown composition, oxygenated bodies, sulfur and nitrogen compounds, organometallic compounds, and adventitious niaterial picked up in the course of refining or delivery. THEORETICAL COh SIDERLTIOY S
AIaxwell has given a rigorous calculation for the determination of the dielectric ronstant of a dispersion of tn.0 different substances of different dielectric constants. hlaxu-ell's original formula can be replaced by the generalized empirical formula, (13) E= = 2 , 8 , € , K
(1)
u ithout great inaccuracy. The so-called logarithmic mixture rule results when the exponent K above is eliminated. The resultant formula rvhich is used in practice ( 2 , 13) is
A N A L Y T I C A L CHEMISTRY
1912
log
tf =
zEe,log
12) where 8' is the dielectric constant of the mixture; t), is the volumetric fraction of zth component, where the total volume, .Set, is equal to I; and E'$ is the dielectric constant of the zth component. This suggests the possible use of the above logarithmic formula for determining the moisture content of a vaporized mixture of fuel oil and water by dielectric means. While the rinciple is applicable, serious limitations are present; the diegctric constants of oils vary and, hence, a range of constants for oils containing identical amounts of water will result. The problem of determining the changes in the dielectric constant of mixtures of oil and water vapor has an additional difficulty. Since the values are 1.00059for air, approximately 1.0035 for oil va or and 1.0126 for water vapor, a dry oil vapor would differ in diegclric constant from one containing 50% water by only 0.0031. Such a small change magnifies the instrumentation problem enormously. E$'
If it is assumed that the logarithmic mixture rule applies to mixtures of sea water and fuel oil and that the dielectric constants of the base oils under consideration are 3 . 0 and 2.3, respectively, while that of water is approximately 80, reference to Figure 1 (using curves 1 and 2 as limits) shows that an unknown mixture having a dielectric constant of 3.5 could contain as little as 5% or as much as 12% water. A second mixture with a dielectric constant of 2.2 would have an apparent negative water content, a conclusion which is obviously impossible. Since a variation in the dielectric constant of dry fuel oils will have a marked effect on the dielectric constant of emulsions of sea water and fuel oil, it has been necessary to determine the magnitude of this factor in a study of S a v y Special fuel oils. If the variation is large, it is evident that, unless the dielectric constant of the dry fuel oil is known, it will be impossible to obtain the correct value of water content. RESULTS
A.
I
Studies were made of 19 samples of oils and approximately 130 emulsions of these oils, containing in some cases as much as 40% synthetic sea water ( 1 )by weight. Selected properties of 11 typical Xavy Special fuel oils, conforming to Specification hIil-F-859A, are listed in Table I. The remaining samples not necessarily conforming to Specification Mil-F-859A consisted of a Venezuelan crude oil, a topped F'enezuelan residuum, a high sulfur-high vanadium fuel oil. a low sulfur-low vanadium fuel oil, and four reference fuels.
I
'
I
Figure 1. Theoretical relationship between dielectric constant and volume per cent of component X
I n employing the dielectric method of measuring water in oil in the liquid state, two possible approaches exist: ( a ) relating the effect of water on the dielectric constant and ( b ) measuring the effect of water on the power factor of the oil. I n both cases the values rise with increase in water content. The logarithmic mixture rule may be applied to liquids (as well as gases) %>-here the corn onents of the mixture are nonpolar and have no permanent dipo?e moment, Application of this theory is demonstrated in Figure 1, curve 1, for a mixture of two substances, A and X,one of which has a dielectric constant of 3.0 and the other a value of 80, respectively. Curve 1 predicts that the maximum dielectric constant to be expected from a mixture of 50% A and 50% X is approximately 15.5, and that a lower adulteration of 20% X results in a dielectric constant of about 5.8. As a second example, curve 2 predicts that the maximum value for another substance, B , with a dielectric constant of 2.3 originally, is approximately 13.5 when adulterated Tith 50% X and that a lower concentration of 2 0 % X results in a dielectric constant of about 4.7. An examination of the theoretical curves indicates that, if the individual substances follow the logarithmic mixture rule, the initial dielectric constant value of the individual components will have a marked effect on the resultant dielectric constant of the mixture.
L_--__(KsI
--
I
,!
500 ---L----lMcl-IO
11,
50
0
K;
IO0
FREOUENCY
Figure 2. Range of dielectric properties obtained for boiler fuel oils as function of frequency
Data a t 10 kc. were obtained by the bridge method; data from 50 kc. to 75 Mc. were obtained with a Q meter. The dielectric constants of emulsions containing more than 5'% synthetic sea water could not be determined satisfactorily by the bridge method. The dielectric constant values are accurate to =!=0.02
1913
V O L U M E 28, NO. 1 2 , D E C E M B E R 1 9 5 6
Table I.
Selected Properties of Some Navy Special Fuel Oils API Viscosity Wat;era Sample Gravity, at Ash, pY KO. 60' F. 122' F. % Distillation
8 9 10 11 a
17 2 14 9 18 3 16 2 15 4 17.3 15 6 15 9 12 8 11 7 17 4
218 212 202 204 218 223 224 211 213 200 141
0.06 0.03 0.04 0.04 0.04 0.01 0.01 0 03
0 05 0 035
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0 1 0 05 0 05 0 05
% by volume.
~
stant of the emulsion as a function of sea water content on a weight basis would be almost identical to the same data s h o r n on a volume basis. The applicability of the logarithmic mixture rule a t 1 &IC.is further demonstrated in Figure 4 by plotting the values of dielectric constant as a function of synthetic sea water content for two emulsions made with two different fuel oils. It is obvious from Figure 4 that the dielectric constant of an emulsion with a given water content is dependent upon the dielectric constant of the dry oil from which the emulsion was made. Also, while the dielectric constant follon s the predicted curve for each mixture (as mentioned earlier), the curves of two 01 more such mixtures are not necessarily parallel. This means that if the water content of t n o emulsions of oils from different sources be changed in like amount, the resultant change in dielectric constant of the emulsions will not necessarily be the same. I n addition, extrapolation of the curves to lOOY0 water content does not yield a dielectric constant of 80 in either case This is not contrary to the logarithmic mixture rule but rather indicates that orientation and association ( 5 , I S ) of the water molecules in the disperse phase of the emulsion are different from that of the bulk synthetic sea water, and that a small correction factor must be applied. The difficulty of interpreting a change in dielectric constant in terms of a change in water content is complicated by the effects of the above factors. The magnitude of error which may be expected in using the dielectric constant method for determining sea water content of
and the power factors to =J=0.0002. All measurements were made within a temperature range of 75' to 85" F. Dielectric Constant. Yalues of the dielectric constant of the 19 oils plotted against frequency are shown in Figuie 2. The curves show that the dielectric constant is frequency dependent, decreasing with rising frequency, although the rate of decrease is not the same for all samples. The results show that relatively water-free fuel oils differ in dielectric constant by as much as 20% a t audio-frequencies and by 9% a t 75 Me. Therefore, the extreme values would differ from a mean value of 2 82 a t 10 kc. by lOy0and from a mean of 2.40 a t 75 Rlc. byapproximately 570. The particular characteristics which are responsible for the wide range in the dielectric constant of the fuel oils a t a given frequency may be ap- - - O 40% EMULSION w I proximated by comparing the known dielectric g 8constants of nonpolar liquids a t equal density to 4 the dielectric constants of 2.58 and 3.06 (the ex' v ~ 3 V EMULSION tremes of the dielectric constant range a t 10 kc. as shown in Figure 2) This would indicate that 0 2 0 % EMULSIOY electronic polarization constitutes about 88% and 74y0respectively, of the total dielectric constant 10% E M U L S I O N 0 5 5 % EMULSION for fuel oils representing the two extremes of those I % EMULSION studied. Because the part of the dielectric con\ORIGINAL FUEL OIL stant which arises from atomic polarization is usually about 1Oy0of that due to electronic po4 0 % SYNTHETIC SEA W4TER larization ( 6 ) , this leaves only 3.27, as arising from energy storage by permanent dipoles in the fuel oil of lower dielectric constant. This proportion changes appreciably for the fuel oil of highest dielectric constant, wherein 18.6% of the NO SYNTHETIC S E 4 WATER lq dielectric constant arises from the presence of permanent dipoles. This indicates strikingly that the original oils differ considerably, not only in the nature of the nonhydrocarbon impurities, but also in the nature of the hydrocarbons present. Dielectric constant data on emulsions were readily obtained with sea water concentrations up to 2 0 5 ; however, some of the emulsions a t 30% SYNTHETIC SE/ the higher concentrations of 30 and 40y0 were WATER rather unstable. Examination of the data obV tained (Figure 3) indicates that the dielectric d 012 20% SYNTHETIC SE, n WATER constant of the misture of synthetic sea water \ and fuel oil increases with increasing sea water content a t all frequencies between 10 kc. and 0 08 10% SYNTHETIC SEl 75 Me. The increase in dielectric constant, in general, follows the predicted curve for mixtures 0 04 as shown previously in Figure 1. This is to be I expected because the densities of the synthetic FREOUENCY sea water and fuel oil components are nearly Figure 3. Variation in dielectric properties of emulsions of fuel oil equal. Thus, a plot of the dielectric consample 3 as function of frequency
'
D
7
0
1914
ANALYTICAL CHEMISTRY
S a v y Special fuel oil emulsions is readily seen from an examination of the upper and lower limits obtained a t 1 Mc. (Figure 5). It should be emphasized that the range shown is representative only of the fuel oils investigated and by no means includes all those which might be obtained under Iiavy Special fuel oil specification (9). The curves show that an unknown emulsion nith a dielectric constant of 2.85 might contain no water or as much as 453, while a second emulsion of dielectric constant of 5.00 might contain as little as 17% or as much as 23%. These approximations hold only if the dry fuel oils from which the emulsions were obtained had dielectric constant values within the limits of the curves-i.e., 2.52 to 2.85. Note that as the
dielectric constant of an unknonn emulsion of any fuel oil thus included in the range approaches the minimum value of 2.52, the error in estimating the inazinmm amount of water present approaches zero. The uncertainty of the dielectric const,ant method of measuring n-ater content of the Kavy Special fuel oil emulsions becomes more apparent by taking the folloning example. If the dielectric constant of an unknon-n emulsion falls Tithin the limits of curves 1 and 2 in Figure 5-e.g.. 2.75-the maximum amount of water indicated is 37,. This does not necessarily represent the true value because it cannot be eshblished that the original Fuel oil from which this emulsion n-as obtained lies within the limits of the range. The real value can be found only by making an actual water determination by laboratory methods or by referring to the dielectric constant of the dry oil from n-hich the emulsion was obtained. Obviously, if rhe dielectric constant of an unknown emulsion lies below the value of 2.52 the fuel oil from 80 rhich the emulsion was obtained was not included in the previously established limits and it Kill be impossible even to estimate the amount of n-ater present. If an instrument n-ere devised based on the dielectric constant -w 6' 0O r method, using a zero-center meter, it would probably be calibrated in one of tn-o ways: (a) based on an average curve midway between the limits of curves 1 and 2, the zero water content corresponding to a dielectric constant of 2 . 6 8 ; ( b ) based on the Ion-er limit as represented by curve 2, where the zero water content corresponds t o a dielectric constant of SAMPLE 3 2.52. - - - - SAMPLE /I If the instrument is calibrated as in (a), values of dielectric constant above 2.68 n-odd alv-a?-s indicate positive values of n-ater content. For values below 2.68, the instrument vould indicate negative values of water content-i.e., less than zero (an impossible situation). This will be true of all fuel oils. If the calibration is based on ( b ) , the values indicated by the 20 instrument n-ill be positive for all emulsions a-ith a dielectric 10 20 30 40 50 constant greater than 2.52. If the dielectric constant of an SYNTHETIC SEA WATER (WEIGHT PER CENT) unknoFn emulsion is less than 2.52, the instrument will indicate Figure 4. Variation of dielectric constant of negative values of water content. This immediately shows that emulsions of fuel oil samples 3 and 11 at 1 Mc.as the dielectric constant of the dry fuel oil is below the range function of per cent synthetic sea water shonn in Figuie 5 . In this case it would be impossible to approximate the true value of the nater content. Any attempt to readjust the instrument to read zero n-odd, in effect, be extending the lon-er limit of the range shown in Figure 5 and, therefore n-ould further increase the magnitude of error in the method. In measuring the water content of emulsions where the dielectric constant of the dry fuel oil lies above 2.85 (above the range shown in Figure 5), the instrument will indicate positive water content whether calibrated by method ( a ) or ( b ) . However, the amount of n-ater present will be less than that indicated. It is evident, then, that for emulsions of Kavy Special fuel oil, n-here the dielectric constant of the dry fuel oil lies Bithin the range of Figure 5, errors in measuring the water content by the dielectric constant method may be as much as 4y6 a t low concentrations t o as much as 7% a t about 25% water content. (At a frequency of 7 5 Nc., these errors range from 3Yc a t low concentrations to as much as 5YG a t about 25YG water content.) For emulsions where I i 1 1 I 1 I I the dielectric constant of the dry fuel oil lies 0 5 IO 15 20 25 30 35 40 45 S Y N T H E T I C S E A W A T E R IviE j H T P E R CENT1 above the range, all readings of water content mill be too high. Where the dielectric constant Figure 5 . Range of dielectric constants at 1 Mc. for sea water emulof the dry fuel oil lies below the range, some sions of Navy Special fuel oil
;'I P
1915
V O L U M E 28, NO. 1 2 , D E C E M B E R 1 9 5 6 readings may be negative and, therefore, meaningless, and the water actual content of the emulsion will be undeterminable. Thus, if the dielectric constant method is to be successful, it will be necessary to employ, as a reference standard, a dry sample of the fuel oil from which the emulsion was obtained. The frequency spectrum beyond 75 Me. was not explored for the follon ing reasons. ( a ) In mixtures of dielectrics in n-hich the components differ in dielectric constant, electrical conductivity, and degree of dispersion, anomalous effects occur a t frequencies near a frequency of maximum absorption. I n a complex mixture such as Navy Special fuel oil, anomalies may be expected as the frequency is raised to higher values, particularly in the region of 1O’O to 10’2 c.p.s. (8). ( b ) At frequencies above 108 c.p.s.(7), the dielectric constant of salt water falls rapidly from approximately 80 to a value of 1.76 a t a frequency of 5 X l O I 4 C.P.S. Thus, the important advantage of the wide differences between the dielectric constant of fuel oil and r a t e r is lost. iilthough the dielectric constant of the fuel oils cannot be obtained a t optical frequencies by ordinary methods, the dielectric constant of hydrocarbons a t optical frequencies follon-s hlaxwell’s lan- relating the dielectric constant of a substance and its index refraction, e’ = n2,where n is the index of refraction of the suhstance (3, 6 , 8 ) . The index of refraction of a hydrocarbon mixture is a function of composition and density (12). Because these f,ictors vary nidely in S a v y Special fuel oils, considerable variation in the index of refraction (and hence, the dielectric constant) remains. Power Factor. I t had been suggested that the pon-er factor (p.f.) might be used as a means of measuring the sea Kater content of fuel oil emulsions. For values less than 0.1 (loyo),the pox-er factor is equal to the ratio of the loss of energy within the dielectric medium to the total energy stored, multiplied by the reciprocal of the dielectric constant. Determination of the poner factor of the Kavy Special fuel oils over the frequency range of 50 kc. through 75 hfc. revealed that the power factor is frequency dependent, exhibiting maxima and minima m-hich vary from sample to sample. There were also Tide differences in values a t comparable frequencies, as shonm graphically in Figure 2. Below 1 Mc., the range of all 19 original oils was greater than that shown in the graph. The per cent power factor of the emulsion below 1 l l c . mas almost identical (within the accuracy of the method) with that of the dry fuel oil in each case. At higher frequencies the per cent pon-er factor increased Tith increasing n-ater content of the emulsion (Figure 3). This is further demonstrated by an examination of Figure 6, n here emulsions of Kavy Special fuel oil sample 3 s l i o ~an ~ orderly and readily observable increase in per cent pon-er factor at a frequency of 40 Me. The fact that per cent poJTer factor of Xavy Special fuel oils varieswidely a t any given frequency and exhibits irregular maxima and minima over the frequency range enormously complicates the use of per cent power factor as a means of estimating water content. This necessitates standardization against a dry sample of the fuel oil being evaluated a t the particular frequency employed. While the presence of sea water in fuel oil samples does raise the per cent poEer factor in a rather uniform manner a t the higher frequencies, belov 1 l f c . the addition of sea water causes no significant change. I t must be emphasized that the per cent poner factor of the dry fuel oils has been found to vary as much as 1 cc to 2 75% a t 40 Me. This is a greater difference in per cent poxw fartor than that of typical emulsions containing from 0 to 40% sea water when measured a t the same frequency. This point is shonm graphically in Figure 3 because the change, even xrith 40% sea lyater, is small in comparison with the difference in initial per cent power factor of the dry fuel oils. Dielectric Loss Factor. I t was also proposed that the dielectric loss factor, if it could be determined directly, might prove a
Figure 6. Yariation in per cent power factor of emulsions of fuel oil sample 3 at 40 M c . with per cent synthetic sea water
-
-1 / /
-
SAMPLE 3 SAMPLE I2
004
b/
/I//
0 03v
0
IO 20 30 40 S Y N T H E T I C SEA WATER (WEIGHT PER CENT)
0
Figure 7. Variation of dielectric loss factor of emulsions of fuel oil samples 3 and 12 at 1 Mc. with per cent synthetic sea water
means of relating electrical and chemical properties of emulsions of sea nater and fuel oil. Dielectric loss factor is defined as the tatio of the loss of energy within the dielectric medium to the total energy stored within it. Dielectric loss factors of the S a v y Special fuel oils examined previously were calculated; the range is shown in Figure 2. The loss factor a t 1 Mc. varies from about 0.03 to 0.104, over a threefold variation. The range of the dielectric loss factor for all 19 oils as received from the supplier --as greater a t the lower frequencies. The dielectric loss factor of emulsions, as exemplified by S a v y Special fuel oil sample 3, rises in an orderly manner u-ith increasing sea water content (Figure 3). The loss factor of the diy oil (about 0.07 at 1 Ale.) is more than trike as great as the lorrer limit (0.03) of the range shon-n in Figure 2. illthough it n as found that dielectric loss factor increased linearly a t a given frequency nith increasing sea water content, examination of the turves for emulsions of S a v y Special fuel oil samples 3 and 12 iFiguie 7 ) indicates that the dielectric loss factor of an emulsion is dependent on the dielectric loss characteristics of the original oil This method of determining sea water in fuel oil emulsions can be employed, therefore, only when data are obtainable on the original dry oil. Conductivity. Because of the success of conductivity methods in estimating the salinity of sea xater ( 4 ) and in determining the water content of petroleum products ( I O ) , it was suggested that this technique might be applied to the measurement of sea water in fuel oil. It was thought that if a given amount of sea water were capable of transporting a known current, then tnice as much sea water would conduct proportionately more. Cnder-
1916
ANALYTICAL CHEMISTRY
lying this suggestion is the hypothesis that the emulsion remains uniform in a static electric field. Experiments revealed that this was not the case and that an emulsion subjected to a constant field associated into chains of water droplets. Similar results have been reported by others (11). This chainlike formation resulted in high conductivity whenever a chain extended from one electrode to another but in low conductivity when the chain was broken. Because the conduction path was not through the mixture per se but through a sporadically generated path of droplets, neither reproducibility nor constancy in measurement was obtained. For these reasons the direct current conductivity method was abandoned. I n order to study the conductivity characteristics of the emulsions in an alternating electric field, the alternating current resistance was calculated from data taken with the Q meter during the dielectric constant measurements. Examination of this property of the emulsions indicated that the sea water content of fuel oil cannot be determined satisfactorily unless similar data are also obtainable on the dry oil. This is to be expected because the same variables that govern power factor and dielectric loss factor determine the alternating current conductivity characteristics
oils from different sources differ in hydrocarbon composition as well as in content of polar materials. When the fuel oils are emulssed with synthetic sea water, the dielectric constant increases with an increase in sea water content. The value of the dielectric constant of the emulsion was found to be a function of the dielectric constant of the dry fuel oil. The increase in dielectric constant corresponding to a given increase in sea water content was not always the same if fuel oils from different sources were used. These variables were found to be somewhat less at frequencies near 75 RIc., but they are sufficiently large to introduce serious errors when the dielectric constant is used t o determine the sea water content of fuel oil emulsions. Where an accuracy of &20% or better is required, the data obtained indicate that the dielectric constant method is inapplicable. LITERATURE CITED
.im. Soc. Testing Materials, D 665-52T, ASTb‘I Standards on Petroleum Products and Lubricants, Sovember 1952. Berberick, L. J., Bell, RI. E., J . A p p l . Phys. 11, 687-8 (1940). Bottcher, C. J., “Theory of Electric Polarisation,” pp. 233-4. Elsevier, Houston, 1952. Bureau of Ships Manual, ”Distilling Plants,” Chap. 58, Articles 58-26 and 58-27, January 1, 1948 Debye, P., “Polar Molecules,” pp. 36-58, Dover Publications, New York, 1929. Glasstone, S., “Textbook of Physical Chemistry,” 2nd ed., pp, 536-7, Van Nostrand, New York, 1946. Hippel, A. R. von, “Dielectric Materials and Applications,” p. 361, Wiley, New York, 1954. Kittel, C., “Introduction t o Solid State Physics,” Chap. 6, Wiley, Kew York, 1953. Military Specification llIL-F-859A, “Fuel Oil, Boiler,” July 31, 1951. Mitchell, J., Jr., Smith, D. M., “Aquametry,” pp. 9-10, Interscience, New York, 1948. Pearce, C. A. R., Brit. J. A p p l . Phys. 5 , No. 4, 136-43 (1954). Sommerman, G. hf. L., “The Dielectric Constant of Petroleum and Petroleum Products” in “The Science of Petroleum,” Vol. 11, pp. 1361-5, Oxford University Press, Cambridge, 1938. Zwikker, C., “Physical Properties of Solid Rlaterials,” pp. 4952, Interscience, S e w Tork. 1954.
SUMMARY AND CONCLUSIONS
This study of certain electrical properties of a number of Navy Special and other fuel oils has revealed that the per cent power factor, dielectric loss factor, and conductivity of the original fuel oils varied widely a t comparable frequencies from 50 kc. to 75 Mc. These characteristics of the emulsions iesponded to changes in sea xatei content in an orderly manner. However, the relationships n-ere of no practical value in measuring the water content because the actual values obtained were dependent on the characteristics of the original dry fuel oils from which the emulsions were made. The dielectric constant of these same fuel oils varied considerably from one oil to another at any given frequency from 10 kc. to 75 Mc. The dielectric constant is frequency dependent, decreasing with increasing frequency, indicating that all oils studied contained qunntities of polar compounds. It is evident that fuel
RECEIVED for review April 27. 1956. Accepted September 19, 1956.
Spectrophotometric Method for Determination of Sugars T. E. TIMELL, C. P. 1. GLAUDEMANS, and A. L. CURRIE M c G i l l University and Pulp and Paper Research Institute o f Canada, Montreal, Que., Canada
A new method for spectrophotometric determination of sugars involves the use of an acetic acid solution of oaminodiphenyl. Aldopentoses, aldohexoses, methyl aldopentoses, hexuronic acids, and certain oligosaccharides as well as methylated monosaccharides can be rapidly and accurately estimated in a concentration range of 20 to 500 y per ml. As Beer’s law is strictly followed throughout and both the reagent and color developed are sufficiently stable, estimations can be based on standard curves. Galactose, glucose, and mannose show identical absorptivity, and the same is the case with arabinose, ribose, and xylose. The method has been found useful in conjunction with paper chromatography. The phosphate salt of o-aminodiphenyl in glacial acetic acid is a good spray reagent for paper chromatograms, with a sensitivity higher than that of the aniline salts.
A
GREBT variety of methods for determination of microquantities of sugars has been developed within the last few years, especially in connection with paper partition chromatography. If direct photometric procedures ( 6 ) are disregarded, all of these procedures involve elution of the sugar from the paper with water followed by a quantitative estimation of the sugar content of the extract. The firEt technique t o be adopted for this purpose, and one that is still widely used ( 5 , 9 ) ,was the Somogyi copper method (16), which is applicable to very small amounts of reducing sugars but is not stoichiometric and also requires several steps. Oxidation with hypoiodite is superior in this respect and also has the added advantage of being quantitative for methylated sugars ( I 1 ) . Unfortunately, all reducing sugars do not react to completion with this reagent, mannose and rhamnose constituting two notable examples ( 7 ) . Oxidation with sodium periodate and estimation of the formic acid formed, as suggested by Hirst and Jones (8), should theoretically be more
