ANALYTICAL CHEMISTRY
610 Table I.
Determination of Polyoxyethylene Stearate
Concn. of ~ ~ 7j't& ~Transmittance ~ , a t 590 Gram,'100 111. 1 2 3 0,500 81 0 80.3 0.400 72 7 73.0 0.300 57.5 60.0 34.0 0.200 37.0 38 0 13.2 15.0 15 8 0.100 0.050 8.8 8.5 8 8 3.5 3 5 0.000 3.5
m p for 5 Detns.
4
80.7 71.7 59.3 37.2 16.0 8.5
4 .5
5 81.3 73.3 61.3 37.5 15.3 9 0 4.0
hverage,
70 80.60 72.64 59.52 36.74
15.06 8.72 3.80
after the addition of the iodine solution. The concentration of the polyoxyethylene stearate solution is then determined from a calibration curve which relates polyoxyethylene stearate concentration to per cent transmittance.
Figure 1 is the calibration curve based upon these data which relates per cent transmittance to polyoxyethylene stearate concentration. I n view of the variations u-hich occur among starches, it is suggested that a calibration curve be established for each batch of starch used. Often the conditions under which the polyoxyethylene stearate solutions are used bring about a hydrolysis of the ester and a precipitation of the stearic acid formed. The polyoxyethylene glycol formed by the hydrolysis remains in solution, and does not interfere with the formation of the amyloseiodine complex. Since the precipitated stearic acid is removed by filtration prior to analysis, only the unhydrolyzed polyoxyethylene stearate remaining in solution is determined by this procedure. Although polyoxyethylene stearate was the only compound studied, this procedure could be adapted to the analysis of many of the compounds which form complexes with amylose.
DISCUSSION ACKNOWLEDGMENT
Table I illustrates the precision with which the polyoxyethylene steaiate concentration may be determined. These determinations were carried out by one analyst over a period of 2 days. An analysis of these data reveals that the 95% limit of confidence (L.C.93) in determining per cent transmittance under these condilimit of confidence is a measure of the tions is +1.41. (The limits about the average of a large number of determinations, within which the means of !%Yoof all duplicate determinations will fall.) This corresponds to about *0.01 gram of polyoxyethylene stearate per 100 ml. over the larger part of the range studied.
The authors wish to thank Steve Harrison for the statistical analysis of the data in this report. LITERATURE CITED
(1) Heald, 9. M.,Paper Trade J . , 113, 39 (1941). 12) Kerr. R. X.. and Trubell. 0. R.. Ibid..117. 25 (1943). i 3 j Blikus, F. F., Hixon, R. M., and Rundle, 'R. E., J.'Arn. Chem. SOC.,68, 1115-23 (1946). (4) Morgan, P. IT..IND.ESG.CHEY.,4h-AL.ED.,18, 500 (1946). ( 5 ) Schoch, T., and ITilliams, C., J . Am. Chem. SOC.,66, 1232 (1944).
RECEIVED August 30, 1950.
Determination of Saturation Temperatures of Inorganic Salt Solutions Refractive Index Measurements CHARLES R. PARKERSON Naval Research Laboratory, Washington, D . C. A s a preliminary step in the study of supersaturation of inorganic salt solutions i t was necessary to devise a method for rapidly and accurately determining saturation temperatures. Using a modified Bausch & Lomb dipping refractometer, a complete analysis was made of the variation of refractive index as a function of temperature and concentration of potassium chloride and potassium bromate solutions. Solutions studied had concentrations such t h a t they were saturated between 25" and 65" C. The temperature range investigated was from 25' to 75" C.
AS
A preliminarj step in the study of supersaturation of inorganic salt solutions i t was necessary to devise a method for accurately determining saturation temperatures. The author desired a quick as well as accurate method. The Bausch & Lomb dipping refractometer was selected as an instrument for the analysis of solutions because of its high accuracy and ease of manipulation. Refractive index measurements as a means of analyzing the concentration of solutions have been a great aid to the sugar industry in the analysis of sugar solutions. Urban and Meloche ( 3 ) used refractive index measurements to analyze solutions of telluric acid, selenious acid, and potassium ferro-
Graphs and tables were obtained from which t h e saturation temperature can be determined from t h e refractive index of the solution and the temperature a t which t h e measurement is taken. The saturation temperature determined is estimated to be within +0.2" C. of the true saturation temperature as indicated by the solubility data used. The main value of this paper lies not in t h e refractive index data presented for the two salts b u t rather in presentation of a technique for precise refractive index measurements of solutions a t elevated temperatures.
cyanide. Washburn and Olsen (4)used refractive index measurements to determine the concentration of sodium hydroxide and hydrochloric acid solutions. Potassium chloride and potassium bromate were selected for study because solutions of these salts were to be used in an investigation of supersaturation phenomena. The solutions investigated were saturated a t temperatures ranging from 25' to 65' C. APPARATUS
A diagram of the apparatus used in taking refractive index measurements is shown in Figure 1.
V O L U M E 2 3 , NO. 4, A P R I L 1 9 5 1 h
611
has been reached, the temperature variesapprosimatel~*0.05 “C. from the cont’rol temperature as measured by a thermometer in vessel 11. The refractometer is mounted as ehown in Figure 1. Refractive index readings of solutions w r e taken with a Bausch & Lomb dipping refractometer, Catalog No. 33-45-25. -4 newer model refractometer, Catalog Xo. 33-45-26, is now offered for sale by Bausch & Lomh. In both models the seal betu.een the metal beaker Containing the liquid being measured and the refractometer is only “liquid-proof.” In either case the liquid-proof joint only decreases the rate of evaporation from that
I.
THERMOMETER DIPPING r W A T E R LEVEL
LARGE NEOPRENE GASKET
STAINLESS STEE S L E E V E BRAZE0 TO ORIGINAL E N FITTING
ORIGINAL N U T T H A T SECURES P R I S M IN P L A C E
BRONZE WASHER SMALL NEOPRENE GASKET TO COMPRESS BEAKER AGAINST RUBBER G A S K E T ,
VESSEL
I
Figure 1. Diagram of Apparatus
PYREX GLASS BEAKER
DIPPING PRISM
It consists of two vessels. Vessel I is a controlled-temperature water bath containing the heating element, temperature regulator, and stirrer. The water from this bath is circulated by pump and connecting rubber hose to vessel I1 and returns through an overflow connection. When equilibrium between the t\To vessels
Figure 2.
Cross Section of Modified Beaker and End Fitting
Thickness of small gasket and large gasket selected so n u t retaining prism would form seals both a t ita inner flange with small gasket and a t its upper end with large gasket
1.37100
-
1.37000
-
1.36900
-
1.36800
-
1.36700
-
1.36600
-
1.36500
:-
I36400
-
W X
‘ W
> c
0 (E
W (E
1.36300
1.36200
-
1.36100
-
1.36000
20
1
,
I
1
1
25
1
,
I
I 1
30
I
I
1
,
1 , 35
I
I
I
I
I
,
I
40
MEASUREMENT
Figure 3.
,
I 45
I
,
,
I
,
,
50
TEMPERATURE
,
,
,
55
I
/
#
60
,
,
I
(
,
65
I
,
,
I L , , , I 70
75
C.
Variation of Refractive Index with Temperature and Concentration of Potassium Chloride Solutions
612
ANALYTICAL CHEMISTRY
Table I,
Solubility Data for Potassium Chloride and Potassium Bromate
Temperature,
c.
20 25
30 35 40 45
;; 60
KC1 ( l ) a , Grams/100 Grams Hs0 34.50 36.02 37.51 38.99 40.39 41.78 43.14 44.48 45.79 47.10
KBrOa (21, Grams/100 Grams HzO
...
8.15 9.63 11.27 13.10 l5,05 17.22 19.70 22.26 24.93 27 7.5 30 90 34.28
65 48,37 70 49.65 75 50.90 80 a D a t a given a t temperatures not reported in the literature \\ere obtained froni curves plotted f r o m d a t a a\-ailable from the authors.
encountered in an open beaker. This type of joint does not provide a positive, vapor-tight seal that prevents evaporation altogether, especially a t temperatures on the order of 75" C. Because absolutely no evaporation was permissible from solutions being measured, it was necessary to modify the beaker fitting the end of the refractometer in order to provide a positive, vapor-tight seal. Several methods of closure were tried on the older model 33-45-25 refractometer. Figure 2 shows the one found to be the most satisfactory. The new model 33-43-26 would require modification in a similar manner. Using this type of closure, satisfactory r e f r a c t i v e i n d e x readings could be made if the precautions which follow were observed. I t is necessary to leave a small air space in the beaker containing the solution to be measured in order to dislodge the layer of small bubbles that frequently collects on the face of the dipping prism. This is done by inverting the refractometer and shaking it, allo~vingthe bubbles to rise to the surface before placing the refractometer upright again. If condensation occurs on the scale lens, steps must be taken to prevent leakage of water vapor from the solution into t,he interior of the refractometer. If the modification is used as shown in Figure 2, the small gasket should be checked to see that it is properly seated. L e a k a g e s o m e t i m e s occurs through the cement joint of the dipping prism. This may be prevented by applying a coat of Glyptal over the external end of the cement joint between the prism and the metal form in which it is mounted.
1.34700
-
1.34600
-
1.34500
-
1.34400
-
1.34300
-
1.34200
-
1.34100
-
134000
-
Solutions were made up to have concentrations such that their saturation temperatures were a t 5" C. intervals between 25" and 65" C. All weighings were made in an air-conditioned room at a temperature which varied but slightly from 25" C. The purity of the potassium bromate and potassium chloride conformed to ACS specifications. Using the solubility data appearing in Table I, each solution was made up by weighing the correct amount of salt and water to the nearest thousandth of a gram. These were aeighed directly into the glass beaker that forms a part of the modified end fitting of the refractometer. The end fitting was assembled and attached to the refractometer. The refractometer n-as then mounted over the controlled temperature bath in such a manner as to submerge the beaker containing the solution to be measured. The temperature of the bath was slou-Iy raised from room tcmperature to approximately 75" C. and was maintained at that temperature for the first reading. The refractometer was removed from the bath frequently and was shaken to facilitate the solution of salt in the beaker. When all the salt in the beaker !vas completely dissolved, sufficient time was allowed for the prism, beaker, and solution to assume the temperature of the bath. This was evident when successive readings of the refractive index remained the same ( 1 0 . 1 scale division). Once the bath temperature was constant, a period of 15 to 30 minutes &-as required for the system to assume equilibrium. Additional readings were taken by lowering the temperature of the bath-for example, in taking the refractive index measurements of a solution saturated a t 25.0" C., the first measurement was made a t 75" C. Additional measurements were taken at 5" intcrvals between 75" and 30" C.; a final reading was taken at ap-
L
1.33600
1.33500
T h e c o m p e n s a t i n g Aimici prism was removed from the refractometer Tvhen the material in which it was mounted softened considcra\~l\- at the maximum temperature of 73' C. Removal of the c o n i p e n P a t i n g p r i s m necessitated the use of sodium light for all readings.
1.33400
1.33300
1.33200
1.33100
PROCEDURE
The f o l l o ~ i n gprocedure vias used in taking refractive index data for both potassium bromate and potasium chloride.
20
25
30
35
40
41
50
Figure 4.
BO
55
MEASUREMENT TEMPERATURE
65
70
15
'C.
Variation of Refractive Index with Temperature and Concentration of Potassium Bromate Solutions
VOLUME
23, NO. 4, A P R I L 1 9 5 1
613
proximately 2" C. above the saturation temperature. This last reading was made a t 27" C. Figures 3 :Lnd 4 were prepared from data taken in this manner. Detailed tables of data on potassium chloride and potassium bromate may be obtained from the author. APPLICATION AhD ACCURACY
Based on the accuracy ( *0.000035) with which refractive index readings can he made using the Bausch & Lomb dipping refractometer, this method of determining the saturation temperature of potassium bromate and potassium chloride solutions is estimated to give values t h a t are within *0.2' C. of the true saturation trmperature, as indicated by the solubility data used. This ckLgree of accuracy is attainable only if the refractometer reading is properly adjusted before use. The reading for dipping prism A v a s adjusted with distilled water according to the manufactuier's instruction. The reading for prism B was adjusted using a sodium chloride solution whose index could be read on both prism A and B. Frequent checks were made to assure proper adjustment of the refractometer. There are, however, certain salts to which the application of this method does not yield sufficiently accurate results to narrant its use. Salts having extremely small change - of solubility with tc,mperature give results which are only moderately accurate-
for example, preliminary work with sodium chloride yields data from n hich the saturation temperature can be read under the bmt conditions t o an accuracy of only * 1.0' C. The accuracy may vary in certain temperature regions for the same salt-for example, greater accuracy can be expected in the case of potassium bromate xhen working 1% ith solutions saturated in the temperature region from 45' t o 65' C. than can be attained in the region from 25" to 45" C. This results because the change in solubility x i t h temperature of potassium bromate is much greater in the higher temperature range; thus, there is a greater change in refractive index per degree change in saturation temperature. Preliminary work with sodium bromate arid ammonium dihydrogen phosphate using this method gives data which promise an accuracy approaching * 0 . l o C. LITERATURE CITED
(1) International Critical Tables, 5'01. 111, p. 106, Xew York, Mc-
Gral%-HillBook Co.. 1928. (2) Seidell, h.,"Solubility of Inorganic and Metal Organic Compounds," 3rd ed., Tol. I, pp. 687, 697, Kew York, D. Van Kostrand Co., 1940. (3) Urban, Frank, and Meloche, V.W., J Am. Chem. SOC.,50, 30039 (1928). (4) Washburn, E. R., and Oisen, A . L., Ibid., 54, 3212-18 (1932).
I
RECEIVED May 25, 1950.
Spectrophotometric Studies of Dithizone and Some Dithizonates Molecular Extinction Coeficient of Dithizone i n Carbon Tetrachloride STANCIL S. COOPER AND SISTER MARY LOUISE SULLIVAN'
S t . Louis Unicersity, S t . Louis, Mo. Uithizone may be prepared pure in solution, b u t not in t h e dry state. Solutions prepared from t h e dry material are of unknown composition. The dithizone content of these and other solutions can be found if its molecular extinction coefficient is known a t its wave length of niaximum absorption in t h e solvent employed. By complexing purified dithizone in carbon tetrachloride w-ith lead, zinc, silver, and mercury(II), coefficients for t h e primary and secondary absorption maxima (at 620 and 450 mp) of dithizone are found to be (34.60 * 0.88) X l o 3 and (20.30 * 0.82) X lo3, respectively. Coefficients for lead, zinc, silker, and mercury(I1) dithizonates are
Q
IT+4?,Y"I'TATIVE spectrochemical micromethods have been espnnded considerably in recent years through the use of dithizoiie (13, 15, 16). Although a large amount of work has heen done to develop new procedures in the application of dithiz o n ~aiid to improve existing ones, in general t,he development has 1)wn :ilong idnipirical lines. S t ~ c ~ r acontributions l treat the more theoretical aspects of clithizonp and its metal complexes (5-5, 8,11,1R,16). Asystematic applicntion of dithizoiie has been delayed by lack of estcnpive distribution studies and by inability to prepare solutions of the reagent in accurately known concentrations. Because quantitative distribution determinations will involve measurements of 1
I're-ent address, T h e B t . 3 I a r y College, Leavenworth, Kan.
also given. The value for dithizone a t 620 nip in carbon tetrachloride can be found by measuring t h e change in optical density of a carbon tetrachloride solution of excess dithizone when shaken with a n equal kolume of a water solution of h o w - n silver content. The coefficient is given as the ratio of the optical density change to the molar concentration of t h e silber i n the w7ater solution. The coefficient in chloroform a t 605 mp can be found in a similar manner. AIolecular extinction coefficients should be valuable in determining the concentration of dithizone and dithizonates. especially in distribution studies involving these compounds.
optical densities of both dithieone arid the dithizonates it is necessary to have a t hand a method of obtaining the concentration of dithizone in solution. Predetermined concentrations of dithizone are difficult, if not impossible, to prepare by dirwt n-eighing bccause the pure compound has not bren prepawd tate. Satisfactory mcthods of purification of the mxtwin1 in solution are in gcneral use; however, such purified solutions are not of known strength. The molecular estinrtion mefficient of dithizone at its wave length of maximum absorption will allow one to establish its concentration after purification, and to determine similar constants for the dithizonates. The limitrd data available for the molecular extinction coefficient of dithizone have been determined on samples obtained direct neighing and
