1583
V O L U M E 21, N O , 1 2 , D E C E M B E R 1 9 4 9 Table I. Weight of Sample, Gram*
4.8146 4.9018 5.4181 5.3021 4.9110 5.1188
Supplementary Determinations
Approximate %of Ethanol i n Final Saponification Mixture NO. Edible Oil A 19 188.4 188.6 19 188.8 19 191.7 67 192.8 65 191.7 67
Average
188.6 182.0
Edible Oil B
5.1381 5.2870 5.0852 4.7905 5.1925 5.1029 5.1663 5.4418 4.8367 5.2680
19 19 19 19 19
66 67 68 66
69
180.4 192.6 191.8 190.8 190.6 194.6 194.8 194.8 194.6 195.2
181.1
194.8
is high and an increased hydrolysis of the soap takes place, one would anticipate higher values for the had-titration of the excess alkali with correspondingly lower saponification numbers." Hence, the results for samples 22 and 23 are anomalous and appear to be in error. Supplementary determinations under similar solvent conditions have been made, in xvhich all samples were saponified under reflux condensers. Some of the samples were then diluted with water to reduce the ethanol content to the indicated values before titration of the excess alkali. These solutions were consequently titrated a t a higher dilution than in
25. 2,4,6-Trinitrotoluene (TNT) NT crystallizes from a variety of organic solvents to give Twell farmed rods, tablets, and plates. The crystals from ethanol me elongated parallel to the e axis but other solventse.g., acetone, ether-ften give crystals elongated parallel to the b axis. There is no evidence of polymorphism for T N T
CRYSTAL MORPHOLOGY (determined by W. C. MeCrone) Cry8td System. Orthorhombic.
the previous experiments, in which additional heating had been employed to drive off the ethanol. As a result, in the earlier experiments the period of saponification had been prolonged beyond a 30-minute period in these cases. However, in none of the experiments was there evidence of incompletely saponified oil. The results of the supplementary determinations are given in Table I. Under these oonditions, with the final ethanol content about 19%, the saponification numbers have an average more than three units lower than when the ethanol content is about 65%a value oharaoteristic of usual correct operating conditions. A further examination of the conditions which gave the high results for the original samples 22 and 23 will be made t o estahlish whether they have resulted from other cause than random error. The data reported in Table I of the original article were subjected to a statistical analysis in that a t test (Snedecor, G. W., "Statistical Methods," 4th ed., p. 75, Ames, Iowa, Iowa State College Press, 1948) was calculated for the two groups representing, respectively, 67 to 72T0and 34 to 6470 of ethanol in the find solution. The weights of oil were ohosen at random in the two groups, so as to eliminate a variance from that source. The group method of calculation was used. The t value caloulated was 0.73. Tho t values necessary for 1% and 5% levels of significance are 3.25 and 2.26, respectively. Thus, there is no significant difference between the two groups. This gives confirmation to the conclusion that the ethanol content can be varied from 34 to 72%. D. T.E m u s J A M EE. ~ REINSCRRE~BER
University of Illinois Urbana, Ill.
LOUISA. W O L L E ~ M A N
Form and Habit. Usually elongated pardel to a or e depending on the solvent; acetone or ether ( b ) , alcohol or melt (c). Shows the forms: braohy pinacoid ( O l O ) , prism (1101, and macrodome (0611. Axial Ratio. a : b : c = 0.375:1:0.153; 0.3793:1:0.1493 ( I ) ; 0.376: 1:0.151 (3). Interfacial Angles (Polar). 061 A051 = 93'46; 110 AT10 = 138" 40. X-RAYDIFFRACTION DATA(determined by W. C. MeCrone and A. Humphries). Cell Dimensions. a = 14.99 A,, b = 40.0 &, c = 6.10 A,; a = 14.85 A,, b = 39.5 H., c = 5.96 A. (S). Formula Weights per Cell. 16. Formula Weights. 227.13. Density. 1.654 (flotation). Principal Lines I/I, 0.42
d
6.990 6.655 5.983 6.587 5.404 5.043 4.967 4.711 4.577 4.406 4.270
Figure 1. Trinitrotoluene Crystals A = Grown from melt et -m temperature; B = grown from melt at about 10" C.; C pmwn fmm a fbYmol mired fusion ~
4.141 3.989 3.844 3.745 3.678 3.497 3.423 3.330 3.255 3.143
1
...
0.03 0.46 0.13 0.07 0.14
.
...
0.05
...
0.21
...
0.05 1.00 0.10 0.11
...
0.07 0.04
d 3.049 2.991 2.915 2.867 2.781 2.721 2.668 2.589 2.539 2.430 2.356 2.293 2.235 2.171 2.132 2.058 2.027 1.994 1. 964 1.921 1.869
1/11 0.24 0.18 0.07 0.08
...
0.12 0.10 0.06
...
0.02 0.10 0.07
... ...
0.08
...
0.03 0.03
...
0.03 0.04
ANALYTICAL CHEMISTRY
1584
OPTICALPROPERTIES (deterIpined by W. C. McCrone). Refractive Indexes (5893 A.; 25’ C.). CY = 1.543 * 0.002 @ = 1.674 * 0.002 y = 1.717 * 0.004. Optic Axial Angles (5893 A.; 25” C.). 2V = 60”. 2E = 114’. Dimersion. .. -~~ -u > ~ r. ~ Optic Axial Plane. 001. Sign of Double Refraction. Negative. Acute Bisectrix. b. Molecular Refraction (. R,) (5893 b.: 25’ C.). = 1.641. R(ca1cd.) = 44.3. R(obsd.) = 49.6. FUSIOK DATA(determined by W. C. hlcCrone). Trinitrotoluene melts a t 81 C. with neither sublimation nor decomposition. The melt supercools readily but usually crystallizes spontaneously m-ithin a few minutes. Crystal growth a t room temperature is very rapid and gives fine curved rods and needles (Figure 1). At temperatures just below the melting point large broad rods are formed; these grow with a characteristic jagged crystal front. The direction of most rapid growth is parallel to c with b, and therefore BX., vertical. A mixed fusio; with thymol (Figure 1 ) shom separate rods with 90” and 67 profile angles. Trinitrotoluene crystallized from the melt and reheated to a temperature just below the melting point will show a characteristic secondary crystallization called “boundary migration”
C
I 061
010
Ira CllO
r
+$
O
(4). LITERATURE CITED
\ b
/
I
Figure 2. Orthographic Projection of Typical Crystal of Trinitrotoluene
(1) Groth, “Chemische Kristallographie,” Vol. 4, p. 365, Leipzig,
Engelmann, 1910.
(2) Hertel, E., and Romer, G. H., 2.p h y s i k . Chem., 22B,280 (1933).
(3) Hultgren, R., J. Chem. Phys., 4, 84 (1936). (4) McCrone, W.? Discussions Faraday SOC.,1949, No.5, 158.
Determination of Vitamin A in the Unsaponifiable Fraction of Fish liver Oils AMERICAKCHEMICAL SOCIETY meeting held in Port13 to 17, 1948, we reported on a simplified method for obtaining the unsaponifiable fraction of fish liver oils for the estimation of vitamin A. The manuscript was not submitted for publication because experimental data were destroyed by explosion and fire in our plant just prior to the meeting, and subsequent limitations in time and facilities have prevented repetition of the original experimental work. During recent months, there has been increasing interest in the use of the unsaponifiable fraction in the physicochemical estimation of vitamin A. In view of this, a number of workers who have investigated our method have urged that the procedure be published, even though supporting data are not available. T THE
A land, Ore., September
Weigh 0.1 t o 0.25 gram of oil, depending on potency, into a 25 X 150-mm. low actinic test tube fitted with a 19/38 female standard-taper joint. Add 0.6 ml. of 50y0 potassium hydroxide solution and 6 ml. of alcohol. Place on a steam bath and reflux under an air condenser for 15 minutes or untihthe oil is completely dissolved. Then remove the condenser, and evaporate the alcohol under vacuum with nitrogen. As soon as this solvent is removed, add about 20 ml. of 1.5% barium chloride solution saturated with chloroform. Allow this mixture to cool, and pipet in exactly 20 ml. of water-washed chloroform. Shake this mixture thoroughly, and centrifuge it until the chloroform layer is clear or nearly so. The barium soaps will form a layer at the
interface. Pipet 10 ml. of the chloroform solution into an amber or red volumetric flask. If vitamin A is to be determined by ultraviolet absorption, add 0.3 ml. of isopropyl alcohol and evaporate the mixture in the volumetric flask to dryness. The volumetric flask in which evaporation takes place can be held partly immersed at an angle in water a t about 60’ to 65’ C. and vacuum applied, under a stream of nitrogen, slowly at first, with an aspirator. Take care not to overheat the residue, and as soon as the last of the solvent has been removed, fill the flask almost to its mark with isopropyl alcohol and mix it thoroughly. Allow the flask to come to room temperature, and then bring up t o volume with isopropyl alcohol. If, after standing for an additional period of 1 to 2 minutes, the solution is cloudy, centrifuge it. The solution can then be used for further dilutions as may be require d. If the Carr-Price reagent is to be used, the chloroform aliquot may be dried by the addition of a few grains of sodium sulfate and then used directly. It is generally believed that, when oils are saponified, the potassium soaps formed group themselves in micelles which have the property of absorbing vitamin A. The fact that it usually takes three or more washes with ethyl ether to extract the vitamin is evidence that vitamin A is difficult to remove from these micelle5 In fact, even with numerous nashings with ethyl ether vitamin A is often not removed quantitatively from the saponification mixture. Precipitating the soaps as barium salts breaks up the
