INDUSTRIAL AND ENGINEERING CHEMISTRY
January 15,1932
67
lowed to fall even a few degrees below 20' C. and the time of extraction is kept a t 4 days, the results obtained will be abnormally low. When a minimum room temperature of 20° C. cannot be maintained day and night during the extraction of water-soluble matter, it appears advisable to bring the inflowing water to 25" C., which can be done very simply by passing it through a block tin coil in a bath maintained a t the desired temperature within a range of *lo.
straight lines whose slopes increase with increasing temperature. It appears reasonable to suppose that the slope of the rectilinear portion of each curve represents the rate of hydrolysis of the hide-tannin compound a t the temperature in question. If this be true, then by extrapolating to zero time the rectilinear portion of each curve, a value would be obtained which would represent the percentage of water-soluble matter in the leather corrected for dissolved tannin. When this is done, for the four curves of Figure 1 the corrected values for TABLEI. EFFECT OF TEMPERATURE UPON RATE OF EXTRACTION OF WATER~OLUBLE MATTERFROM OAK-BARK-TANNED HIDE water-soluble matter show an extreme variation of less than 0.5 per cent, indicating that the distinction between fixed POWDER tannin and water-soluble matter is not affected by change in INCREASE PER DEQREE DAYS APPARENT WATER-SOLUBLE IN TEMPERATURE temperature of extraction over the range studied. WA0EED MATTBR FOUNDAT: INTERVAL AT: 10' C. 20' C. 30" C. 40' C. 10-20° C. 20-30' C. 30-40' C.
1 2 4 8 16 32
%
%
16.8 19.8 22.7 27.1 30.0 31.4
18.9 23.0 27.0 29.6 30.9 33.6
% 20.8 (22.6) 27.9 30.4 32.0 35.1
% 21.8 24.5 28.6 30.6 32.7 37.0
%
0.21 0.32 0.43 0.26 0.09 0.22
%
0.19 (-0.04) 0.09 0.08 0.11 0.15
LITERATURE CITED
%
0.10 0.19 0.07 0.02 0.07 0.19
The shape of the several extraction curves is interesting in that these curves do not converge, but rather tend to become
(1) Merrill, H. B., J. Am. Leather Chem. Assom., 24, 244 (1929). (2) Wilson, J. A., Ibid., 16, 264 (1921). (3) Wilson, J. A., and Merrill, H. B., Ibid., 21, 2-30 (1926). RECEIVED July 8, 1931. Presented before the Division of Leather and Gelatin Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12,1930.
Binary System Carbon Tetrachloride-Ethylene Dichloride Their Boiling Points and Specific Gravities as Aids in Analysis H. D.YOUNGAND 0. A, NELSON, Bureau of Chemistry and Soils, Washington, D. C.
s
INCE carbon tetrachloride-ethylene dichloride mixtures have been used as fumigants against moths and other insects ( I ) , it has become increasingly important to find a rapid and reliable method of ascertaining the ratio of the two components in such a mixture. Carbon tetrachloride contains 92.20 per cent chlorine and ethylene dichloride 70.65 per cent, the difference being 21 -55 per cent.. To detect a difference of 1 mole per cent in the composition of a mixture of these compounds by a determination of the chlorine content would therefore require that this constituent be known to the nearest 0.2 per cent. Such a degree of accuracy might possibly be attainable by the best methods now in use, but only by taking extreme precautions with-consequent loss of time.
ANALYSISBY PHYSICAL METHODS Three physical constants-refractive index, specific gravity, and boiling point-were considered as offering bases upon which to found a method of analysis. Rosanoff and Easley (.2) found the refractive indices of carbon tetrachloride and ethylene dichloride at 25.2' C. to be 1.45730 and 1.44218, respectively. As these figures are so close together that extreme care under very closely controlled conditions would be necessary to get any results a t all, nothing further was done with this factor. The specific gravities determined on purified samples prepared by prolonged drying of chemically pure reagent materials over calcium chloride followed by distillation, were found to be 1.591 for carbon tetrachloride and 1.252 for ethylene dichloride, both at 20" C. This is a more favorable difference, and the whole composition-specific gravity relationship was therefore determined.
The pure compounds were mixed in the following ratios (mole per cent): 100% CCL; 90% CC14 and 10% CzH4C12; 80% CCL and 20% CZH,Clz;. . . 0% ccI4 and 100% CZH4Cl2. The observed specific gravities of these mixtures are given in Table I and shown graphically in Figure 1. As would be expected, the specific gravity-composition curve shows no irregularities, so a determination of this constant alone might be used to ascertain the composition. The total range of specific gravity is about 0.340, equivalent to approximately 0.0034 per 1 mole per cent change in the concentration of one of the constituents. Therefore, specific-gravity determinations can be made to yield analyses with an accuracy of * 1mole per cent, always with the assumption, of course, that the mixture contains no impurity. GRAVITIES AND BOILINQ POINTS OF TABLEI. SPECIFIC CARBONTETRACHLORIDE, ETHYLENE DICHLORIDE, AND MIXTURES OF THE TWO COMPOSITION IN MOLES CClr CnHdCla
%
%
100 90 80 70 60 60 40 30 20 10 0
0 10 20 30 40 50 60 70 80 90 100
SPECIFIC GRAVITYBOILINQ POINT AT 20"/20° AT 760 MM. O
1.691 1.563 1.531 1.600 1.469 1.435 1.402 1.367 1.330 1.292 1.262
c.
76.52 76.82 75.42 75.30 75.39 75.74 76.39 77.26 78.49 80.23 82.85
The difference in boiling points between ethylene dichloride and carbon tetrachloride is 6.33' C. As boiling-point differences can be determined to about *0.002' (the limit of accuracy of a Beckman thermometer), it is evident that very
ANALYTICAL EDITION
68
Vol. 4, No. 1
compositions are possible for each boiling point. Over this range, therefore, it is essential to determine the specific gravity in addition to the boiling point. For mixtures having compositions between 80 mole per cent carbon tetrachloride20 mole per cent ethylene dichloride and 60 mole per cent carbon tetrachloride-40 mole per cent ethylene dichloride, the composition can be determined more accurately by specificgravity determinations, as over this range the change in boiling points with change in composition is very slight.
small changes in concentration might be detected by boilingpoint determination in this system. For this purpose it was necessary to establish the entire composition-boiling point relationship in the system, since, so far as could be found by examining the literature, this had not been done previously.
DISTILLATION OF BINARY MIXTURECARBON TETRACRLORIDE ETHYLENE DICHLORIDE Since a boiling-point curve for mixtures of carbon tetrachloride and ethy!ene dichloride had been obtained, the determination of the composition of the vapor phase for all mixtures of these compounds was next attempted. The distillation apparatus used, a modification of which will be described in a subsequent publication, consisted essentially of the boiling-point apparatus mentioned above, to which was attached an equilibrium chamber suggested by the work of Rosanoff, Lamb, and Breithut (3). If one could add to the boiler of this apparatus a mixture having exactly the same composition as the initial portion of the distillate and continue the addition a t the same rate as distillation proceeds, FIGURE 1. SPECIFIC GRAVITIES OF MIXTURES OF PURECOMthe composition and hence the boiling point of the solution POUNDS would obviously remain constant, and the distilIate would be The apparatus used for determination of boiling points identical in composition with the vapor of the original mixwas that developed by Swietoslowski (4). It is claimed for ture a t its boiling point. To approximate this condition the this apparatus that "it is easy to detect the difference in the procedure described below was followed. The distillation was carried out in two steps. During the boiling temperature caused by removing the apparatus from first step the two constituents were added alternately in small the level of the laboratory table to that of the floor." All boiling-point determinations were made at atmospheric increments while the boiling temperature of the solution was pressure, and were calculated to 760 mm. by Landolt's equa- watched very closely. It was possible in this way to keep tion dT/dP = O.O43O/mm. The accuracy of this equation the boiling point constant to 0.05" C. After about 125 cc. was confirmed experimentally by observing the boiling points of both compounds, as well as of several of the mixtures, at different pressures. The results are given in Table I, and are represented graphically by the lower curve in Figure 2. TABLE 11. COMPOSITION OF DISTILLATES FROM VARIOUS CARBON TETRACHLORIDE-ETHYLENE DICHLORIDE MIXTURES B. P. OF SOLN.AT 760 WM. e
c.
76.20 76.96 76.86 76.71 76.78 76.62 78.73 80,27 SO. 39 81.69
COMPOSITION OF SOLN.IN MOLES CClr CnH4Ck
%
%
96.0 92.3 90.0 88.0 60.6 37.0 18.6 9.7 9.1 4.0
4.0 7.7 9.1 12.0 49.4 6.7.0 81.6 90.3 9o.g 96.0
COMPOSITION OF B. P. OF I N MOL^^ DISTILLATEDISTILLATE Cc1r CIH~CI~ AT 760 MM.
c.
76.86 76.68 75.66 76.60 76.63 76.93 77.23 78.63 78.61 79.81
%
%
90.7 87.6 84.8 83.1 66.7 47.3 31.0 20.2 18.6 14.1
9.3 12.6 16.2 16.9 44.3 62.7 69.0 79.8 81.6 86.9
The composition-boiling point data show that there is a minimum boiling point of 75.30' C. a t a concentration of approximately 70 mole per cent of carbon tetrachloride. The data show also that from 100 per cent ethylenedichloride to 40 mole per cent carbon tetrachloride60 mole per cent ethylene dichloride, the composition can be determined to an accuracy of better than 0.10 per cent by reading the thermometer to 0.01" C., but from 100 per cent carbon tetrachloride to 40 mole per cent carbon tetrachloride60 mole per cent ethylene dichloride, it is obvious that the composition cannot be ascertained to such a high degree of accuracy for the reason that over this range the temperature change with change in composition is much less. Also, since the curve passes through a minimum at 70 mole per cent carbon tetrachloride-30 mole per cent ethylene dichloride, two different
-
"'m7
ccr,
'
I
I
I
I
I
5 0 % CcLr
sa%
c~r~cr,
COMPOSITION-MOLC PCRCcNT
I
I
I
I
100 i: c 2
u, c!,
FIGURE2. BOILINQ POINTSOF ETHYLENE DICHLORIDE AND CARBON TETRACHLORIDE AT DIFFERENT TEMPERATURES
had distilled over, the distillate was poured into a dropping funnel and returned to the boiler a t the same rate as distillation proceeded. In this way it was easy, during the second stage of the distillation, to maintain the boiling temperature constant to within =+=O.0lo C., indicating no change in concentration of the solution greater than 0.1 mole per cent. The final distillate was analyzed by determining its boiling point and reading the ratio of the components from the curve of Figure 2. The composition of the boiling liquid with which this condensed vapor is in equilibrium was naturally determinable in the same way from its observed boiling point. The
January 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
results are tabulated in Table I1 and shown graphically in the upper curve of Figure 2. As is Usual in Systems having a minimum boiling point, the vapor curve lies wholly above the liquid curve and bends to become tangent to it a t the minimum boiling point, The composition of all corresponding liquids and vapors are given by the points on the curves having equal ordinates.
69
LITERATURE CITED (1) Cotton and Roark,
s.&on.
Entomoz., 20, 636-9 (1927).
(2) Rosanoff and Easley, J . Am. Chem. SOC.,31, 970 (1909). (3) RosaOff, Lamb, and Breithut, Ibid.9 31,448 (1909).
(4) Swietoslowski, J . Chem. Education, 5, 469 (1928). RECEIVEDJune 24, 1931. Presented before the Division of Agricultural and Food Chemistry at the 81st Meeting of the American Chemical Sooiety, Indianapolis, Ind., March 30 to April 3, 1931.
Optical Identification of Strychnine CHARLESF. POEAND JESSE E. SELLERS,University of Colorado, Boulder, Colo. o i l 4 e., they will not be visible when the long direction of the crystal is parallel to the direction of vibration of the lower nicol prism (the 6 o’clock and 12 o’clock direction in the ordinary polarizing microscope.) The remaining two refractive indices may also be determined by substituting liquids of the proper refractive index. These determinations, however, require a petrographic microscope and some knowledge of optical mineralogy. In a like manner the remaining portions may be tested by adding an excess of potassium chloride, potassium bromide, and potassium iodide, respectively. An excess of the salts may be added so as to reduce the solubility of the strychnine salt. Care must be taken, however, that the concentration is not so great as to cause the alkali halide to precipitate out when cold. If this should happen, these halides may be recognized immediately under the microscope, since all of TABLE I. OPTICAL PROPERTIES OF SEVERAL STRYCHNINE SALTS them are isotropic. After the strychnine salt has been COMPOUND CLASS REPRACTIVE IND~X 2 8, O C. SYSTEM washed and dried, the crystals are submerged in oils of the a 8 Y proper refractive indices and the refractive indices of the Stryohnine Monoclinic 1. 59Sa 1.654 perchlorate Biaxial 1.589 crystals thus determined. The proper oil may be selected by Strychnine Orthorhombic referring to the indices given in Table I. It is often difficult 1.662 hydrochloride Biaxial 1.609= 1.627 Stryohnine to get all three of the refractive indices for a given crystal. 1.730 Monoclinic 1.650 hydrobromida Biaxial 1.646‘ Strychnine In such cases finely divided glass wool may be used to obtain 1.730 i Monoclinio Biaxial 1.6570 1.665 hydroiodide the crystals in an end position. Index in lengthwise direction. If desired, tests may be extended to other salts of strychnine. The four selected are the most satisfactory because METHOD OF DETECTION of their slight solubility and because the refractive indices are The sample of suspected material is purified in the usual readily determined, especially when the elongated crystal is manner by means of organic solvents. It is finally extracted oriented with its long axis parallel to the direction of vibrawith pure chloroform from an alkaline solution. The chloro- tion of the lower nicol. The alkaloid itself may be used, but form is then evaporated and the strychnine is dissolved in a it presents more difficulties than the above-mentioned salts. small amount of 5 per cent acetic acid. The amount depends After the presence of strychnine has been determined, it is upon the quantity of strychnine present. The solution is well to repeat the determination and, a t the same time, perdivided into four equal parts, each of which should contain form the tests with a suitable amount of strychnine of known at least 0.25 cc. of solution with a strychnine content of abobt purity. 0.5 mg. The amount of strychnine in solution may require In addition to the refractive indices, other optical tests, adjusting by concentration or dilution. If the quantity is such as habit, sign, extinction, elongation, interference too small, no strychnine salt will separate out after the addi- figures, polarization colors, optical angle, dispersion, etc., tion of the reagent and, if too concentrated, the crystals will may be determined. be too small. After being divided, the solutions are placed in A number of alkaloids, which may be extracted in the 50-cc. beakers and heated to boiling. They are tilted before same group with strychnine, such as atropine, codeine, bruthe reagents are added so that the solutions will collect in a cine, morphine, etc., were studied. None of these showed small area. To the first portion is added a slight excess of enough interference to vitiate the test. perchloric acid (or potassium perchlorate), the whole is It appears that the above-described tests, together with warmed, and allowed to crystallize out very slowly. The the ordinary color tests, give a conclusive means for the posiliquid is removed and the crystals are washed with one drop tive identification of strychnine, even if the refractive index of water. The filtrate and water may be carefully soaked up in the lengthwise direction only is determined. with filter paper, or a microfilter may be prepared by placing a small plug of absorbent cotton in the tip of a medicine dropLITERATURE CITED per and drawing the liquid into the dropper. The crystals are (1) Poe and O’Day, J. Am. Pharm. Assocn., 19, 1292 (1930). allowed to dry in the air and are then mounted in oil of a re- (2) Poe and Sellers, J . Am. Chem. Soc., 54, 249 (1932). fractive index of 1.598. If the crystals are strychnine perchlorate, they will show the same refractive index as the R E C W V ~August D 11,1931. OST of the chemical tests usually used for the detection of strychnine depend upon color reaction. As has been shown by Poe and O’Day (l), the color reaction with Mandelin’s reagent is not specific and may be given by a number of organic compounds other than strychnine. This paper describes a method for the detection of strychnine by means of the optical properties of some of its salts. A previous paper (d), in which the literature was reviewed, gives the optical-crystallographic data for a series of salts of strychnine. From the study of a number of these salts, it has been found that four, owing to their low solubility in water, are especially suitable for use in the optical detection of this alkaloid. These salts appear, together with some of their optical-crystallographic properties, in Table I.
