Asbestos in Permanganate Titrations R. W. CURTISAND J. FINKELSTEIN Division of Quantitative Analysis, The College of the City of New York, New York, N. Y.
F
OR the determination of calcium in limestone and in other silicate rocks, the usual procedure (2, 6 , 7 , 8) is to precipitate the calcium as calcium oxalate from the filtrate from which silica, iron, aluminum, and manganese have been removed. According to the procedure of the authors cited and of many others, if the calcium in the purified precipitate is to be determined volumetrically, filter paper may be used for the filtration. I n order to set free the oxalate ion, the precipitate is treated with sulfuric acid, and for this purpose a concentration of acid varying from 3 N to 6 N is recommended by different authors. The question whether or not there would be a reaction with the cellulose or other constituent of the filter paper, yielding a product oxidizable by potassium permanganate, was considered by McBride and Sherer (5), who dealt principally with “extracts” obtained by passing water and dilute solutions of certain reagents through the paper. Most of the results show negligible effects, corresponding to about 0.03 cc. of 0.10 N potassium permanganate, though in one case 0.24 cc. was used up. The record shows no results obtained in titrations in which the permanganate took part in one of its usual oxidation reactions. Everyone must have observed the color changes that occur when a drop of permanganate is placed on dry filter paper. Two authorities (4, 9) recommend that when the solution containing the oxalate is treated with permanganate, the filter paper on which the calcium oxalate was received be placed on the wall of the beaker and put into the solution near the end point. The experiments, the results of which are shown in the tables, were carried out to test the question further. Table I shows the standardization of approximately 0.15 N potassium permanganate performed on different days according to approved procedure (S). TABLEI. STANDARDIZATION OF POTASSIUM PERMANQANATE SODIUM OXALATE Qrom 0.3252 0.2602 0.2795 0.3110 0.2550
POTASSIUM PERMANQANATE Cc. 35.25 28.13 30.23 33.60 27.56
Av.
OXALATE EQUIVALENT Gram 0.009265 0.009250 0.009246 0,009256 0.009252 0.009254
TABLE11. TITRATION IN PRESENCE OF FILTER PAPER POTASSIUM PERMANQANATE
cc. 31.58 30.99 35.56 35.09 34.42
TABLE111.
STANDARDIZATION O F POTASSIUM PERMANGANATE SODIUM POTASSIUM OXALATE OXALATB PERMANQANATE EQUIVALENT Gram c c~. . Gram 0.3143 0.008215 38.26 0.2955 0.008213 35.98 0.3172 0.00821s 38.59 0.2653 0.008216 32.29 0.008218 34.80 0.2860 0.3174 0.008216 38.60 Av. 0.008216 ~
Table IV shows the titration of weighed portions of standard sodium oxalate carried out in exactly the same way, except that asbestos from a Gooch filter was added. TABLEIV. TITRATION IN PRESENCE OF ASBESTOS SODIUM OXALATE Gram 0,2603 0.3295 0,2829 0.3391 0.3388 0.2533
POTASSIUM
OXALATE
EQUIVALENT
PERMANGANATE
cc.
31.68 40.09 34.43 41.47 41.24 30.97
Av.
Table I1 shows the effect when this standard potassium permanganate solution was used to titrate weighed portions of standard sodium oxalate, according to the same procedure, but with a piece of quantitative filter paper (Carl Schleicher and Schull-Blue Ribbon, No. 589) in the solution. SODIUM OXALATE Gram 0.2892 0.2842 0.3260 0.3217 0.3150
per thousand, and would make a difference of 0.70 per cent in a typical limestone carrying 64 per cent of calcium as calcium oxide. When the Gooch filter is used for separating the precipitate of calcium oxalate, the asbestos felt is usually introduced into the solution to be titrated, because suction must be used and the calcium oxalate cannot be dissolved satisfactorily on the felt, as the acid does not remain long enough in contact with it. A search of the analytical literature failed to reveal the record of any tests to determine whether or not there is any effect when oxalate is titrated by standard potassium permanganate in the presence of asbestos from an ordinary Gooch felt. A new standard permanganate solution was prepared and standardized as above ( 3 ) . Table I11 shows the standard values obtained on different days showing the stability of the solution.
OXALATE EQUIVALENT Gram 0,009158 0.009168 0 . 0 0 9 170 0.009168 0.009178 Av. 0.009168
Gram 0.008216 0.008219 0.008216 0.008217 0.008215 0.008216 0.0082165
Thus it is shown that filter paper has an effect in titrations with potassium permanganate, and that asbestos has no such effect. When using filter paper, it must be added to the solution to accomplish a quantitative transfer, because some of the calcium oxalate adheres to it (Q), while the asbestos mat, not affecting the results a t all, furnishes a means of transferring the precipitate quantitatively. When using the Gooch filter, the creeping action of calcium oxalate ( I ) , which may result in serious loss, is not encountered. It was found, moreover, that asbestos in suspension while stirring provided a background in the solution that made the detection of the end point easier. As a result of this work, it appears that the Gooch felt is preferable, when it is desired to determine oxalate ion by potassium permanganate.
SUMMARY
Thus there appears to be a reaction, using up, on the average, 0.33 cc. of the standard potassium permanganate solution. This corresponds to an error of about ten parts
Asbestos does not react with volumetric potassium permanganate solutions. Filter paper reacts to an appreciable extent. The presence of the asbestos is an aid in the determination of the end point.
318
September 15,1933
INDUSTRIAL AND ENGINEERING
LITERATURECITED Fales, “Inorganic Quantitative Analysis,” p. 236, Century, 1925. Hillebrand, W. F., and Lundell, G . E. F., “Applied Inorganic Analysis,” p. 502, Wiley, 1929. Kolthoff, I. M., and Mensel, H., ti-. by Furman, “Volumetric Analysis,” p. 279, Chapman & Hall, 1929. Low, “Technical Methods of Ore Analysis,” 6th ed., p. 67, Wiley, 1922. McBride and Sherer, J. Am. Chem. Soc., 39, 928 (1917).
CHEMISTRY
319
(6) Scott, “Standard Methods in Chemical Analysis,” 4th ed., Vol. I, p. 108, Van Nostrand, 1927. (7) Talbot, “Quantitative Chemical Analysis,” 7th ed., p. 191, Macmillan, 1931. (8) Treadwell, F. P., and Hall, W. T., “Quantitative Analysis,’’ Vol. 11, p. 530, Wiley, 1924. (9) Washington, H. S., “Chemical Analysis of Rocks,” 4th ed., p. 294, Wiley, 1930. RECEIVED May 4, 1933.
Estimation of Total and Bound (D) Gossypol in Cottonseed Meal A Modified Method F. H. SMITH AND J. 0. HALVERSON, Agricultural Experiment Station, Raleigh, N. C.
G
OSSYPOL in the cottonseed is readily soluble in ethyl ether. However, probably because of the influence of heat, pressure, and moisture, when expressing the oil from the crushed seed in the commercial manufacture of the cottonseed meal, the greater part of the gossypol left in the meal becomes insoluble in ethyl ether. This insoluble part is known as bound or (D) gossypol (I, 2 ) . The method used by Carruth (4) for the estimation of bound gossypol follows: Fifty grams of meal, having been previously extracted with ethyl ether, are saturated with 100 cc. of aniline, heated for 5 minutes a t 110” C., with constant stirring; then as much of the aniline as possible is removed immediately by a Biichner funnel and, after cooling sufficiently, the residue is washed with ethyl ether in order to remove the remaining aniline. The filtrate and washings are concentrated by distillation to a volume of 5 to 10 cc. The residue is washed with ethyl ether into a small beaker and allowed to stand one week in order to crystallize. The precipitate of dianiline gossypol is then filtered through a weighed Gooch crucible, and dried a t 100” C. to constant weight. The dianiline gossypol is converted to gossypol by the factor 0.775. TABLEI. THE ESTIMATION OF TOTAL GOSSYPOL (CHIEFLY BOUND)IN COTTONSEED MEAL1578 CARRUTH METHOD %
%
%
Mg.
%
0.920 0.812 0.929
0.941 0.961 0.972
1.115 1.060 1.140 1,090 1.080 1.110 1.120 1,102
19.6 19.4 18.8 19.0 19.0 19.3
98.0 97.0 94.0 96.0 95.0 96.5
19.2
95.9
... I
.
.
... ... Av. 0.881 a
MODIFIED OF GOSSYPOL CARRUTH PROPOSED RECOVERY METHOD BY PROPOBED METHODO METHOD
... ... .
.
I
... 0.958
..
..
20 mg. gossypol uaed.
From a study of the factors concerned in the determination of gossypol by a modified method (S),certain improvements in the method of Carruth for bound gossypol were apparent. These were a more complete removal of the gossypol from the meal; the elimination of some decomposition of probably dianilirie gossypol by distilling off the excess aniline under reduced pressure, in which the greater part was distilled under 110” C. (just before completion, however, the maximum temperature of 140” C. was reached); a more complete precipitation of dianiline gossypol was also possible by the elimination of the ether used in the precipitation and washing since the precipitate is somewhat soluble in this
reagent, The precipitation of dianiline gossypol was facilitated by the use of 75 cc. of petroleum ether and 10 cc. of ethylene glycol in which dianiline gossypol is quite insoluble. The precipitate was washed with petroleum ether, then with a small amount of alcohol, and finally with water. With these modifications an average of 0.958 per cent gossypol was obtained from meal 1578, compared with 0.881 per cent by the method of Carruth, or an increase of 0.077 per cent. For the convenience of using smaller charges than 50 grams and 100 cc. of aniline the following method was worked out for total and bound gossypol. In order to obtain the total or the bound gossypol, the meal is first extracted on the Pickel extraction apparatus with petroleum ether and with ordinary ethyl ether, respectively, then dried, and stirred. All results reported in Table I are for total gossypol, inasmuch as the amount of ether-soluble gossypol in a charge of 2 grams is small, being less than 2 mg., and since the bound gossypol constitutes 90 per cent or more of the total. The accuracy of the proposed method for the determination of bound gossypol is also better shown by the determination of total gossypol, since it has been found that the amount of ether-soluble gossypol is variable, depending upon the moisture content of the meal (in press). MODIFIEDMETHODIN DETAIL Place a charge of 2 grams, ground to pass through a 40-mesh sieve, in a medium or porous alundum filter crucible of 25 cc. capacity, extract in the Pickel apparatus 3 hours with petroleum ether in order to remove the crude oil, or 72 hours with ethyl ether for the ether-soluble gossypol in the estimation of total and bound gossypol, respectively. Dry the crucible and contents, stir the meal, and place the crucible with contents in a clean Pickel flask. Pipet (by suction) 5 cc. of aniline onto the meal. Then add 15 cc. of alcohol (90 per cent) to the flask and extract for 24 hours on the Pickel apparatus. Remove the flask, and transfer the extract to a 200-cc. Erlenmeyer flask with the aid of ethyl ether and a funnel. (The raffinose precipitated by the ether goes into solution during the process of precipitation. Any crystals of gossypol that may be adhering to the Pickel flask are transferred to a weighed Gooch crucible with the aid of water.) Remove the alcohol and ether by reduced pressure, then add 7 cc. of ethylene glycol and 10 cc. of ethyl ether to the residue. Digest on the steam bath. After the ether begins to boil, add water with shaking, a t 3-minute intervals
