JANUARY 15, 1938
ASALYTIC.4L EDITION
Moisture Content of Powdered Derris and Cube Roots I n Table I1 are given the values for moisture content of the powdered derris and cube roots determined by drying 2-gram samples a t 106" C. for 2 hours. Two days' additional drying of some of the samples caused no significant additional loss in weight. It will be noted that the values range only from 4.9 to 8.5 per cent. I n view of this small variation the rotenone values have not been corrected for moisture content of the sample. Work done in the writers' laboratories indicates that it is preferable not to dry the sample before extraction. I n cases in which a preliminary drying has been made the results for rotenone and the purity of the separated solvate have usually been slightly lower than on the undried root. There are indications also that drying renders extraction more difficult. Some samples were dried a t 100" C., and others a t 50" C . under vacuum. I t is possible that drying a t room temperature, such as in a vacuum desiccator, would not interfere with the rotenone determination. Such drying, however, seems unnecessary for the analysi- of the usual samples received in this country.
Summary and Conclusions I n the analysis of finely powdered samples of derris and cube roots a method involving treatment with chloroform a t room temperature followed by removal of an aliquot of the filtered extract gives satisfactorily complete extraction of the rotenone. Fineness of the sample is a n exceedingly important factor in obtaining complete extraction by any method. If coarse samples are ground so that a t least 95 per cent passes a 60-
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mesh sieve, they will usually give satisfactory extraction b y the aliquoting procedure. Samples containing a high ratio of rotenone to total extractives were found to be more difficult to extract than those with loTver percentages of rotenone. T h e n the ratio of rotenone to total extract was about 40 per cent or over, particularly in the case of derris roots, it was necessary to employ extraction a t room temperature with successive lots of chloroform in order to obtain satisfactory extraction of the rotenone. This method should also be employed as a check whenever there is doubt as to the completeness of extraction by the aliquoting procedure. Cube roots in general are more readily extracted of their rotenone content than are derris roots. The moisture content of derris and cube roots as received in this country has not been found to be sufficiently great to interfere with their analysis, and hence preliminary drying of samples seems unnecessary.
Literature Cited Beach, D. C., Soap, 12, N o . 7, 109, 111-12 (1936). Begtrup, F. L . , Dansk Tids. Farm., 11, 6-12 (1937). Cahn, R. S.,and Boam, J. J., J . Soc. C h e m In?., 54, 37-42T (1935).
Danckwortt, P. W,. and Budde, H., Deut. Tiertirztl. Tochschr., S o . 43, 677 (1933). Georgi. C. D. V., Lambourne, J., and Teik, G. L., X a l a y a n 4 g r . J., 25, 187-200 (1937). Jones, H. A , . ISD.ESG. C H E X I . , Anal. Ed., 5,23-6 (1933). Jones, H. .A,, Ibid., 9 , 206-10 (1937). Jones, H . A , , and Smith, C . M., I b i d . , 5, 75-6 (1933). Roark, R . C . . Mafalayan Agr. J . , 18, 455-8 (1930). Rowaan. P. A., Cliem. T e e k b l a d , 32, 291-5 (1935). Seaber, W. M., J . SOC.Chem. Ind., 56, 168-73T (1937). Torsley, R . R . LeG., Ibid., 55, 349-57T (1936). RECEIVED December 10, 1937.
Standardizing Silver Nitrate Volumetric Solution ROBERT D'ORAZIO 767 East 237th St., New York, N. Y.
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HE author has used to good advantage the following short method for the standardization of volumetric silver nitrate. A volumetric hydrochloric acid solution is exactly neutralized, using a standard alkali solution. The chloride salt formed is then determined by titrating with a volumetric, silver nitrate solution, using potassium chromate as indicator. The number of cubic centimeters of hydrochloric acid is exactly equivalent to the number of cubic centimeters of standard alkali, which, in turn, is exactly equivalent to the number of cubic centimeters of silver nitrate. Thus, if any one of the above is known, the other two can be determined. The author used this method to standardize silver nitrate against sodium hydroxide standard volumetric solution, for chloride determinations. Sodium hydroxide was used as the standard in preference to hydrochloric acid, since in this particular laboratory standard hydrochloric acid was not available as a stock reagent. Place 25 cc. of 0.1 -V hydrochloric acid, accurately measured from a buret, and about 25 cc. of distilled water in an Erlenmeyer flask of about 200- to 300-cc. capacity. Vsing phenol-
phthalein test solution as indicator, titrate to a faint pink with the standard 0.1 N sodium hydroxide volumetric solution. Add 2 cc. of a 5 per cent potassium chromate test solution and titrate with the silver nitrate solution, to the first red tinge. The cubic centimeters of silver nitrate, consumed in the titration, are exactly equivalent to the cubic centimeters of the standard sodium hydroxide. When checked against the thiocyanate volumetric method and the silver chloride gravimetric method, good results were obtained and the time required was only a few minutes as against hours in these two other methods. This principle can also be applied to the standardizations of potassium permanganate and oxalic acid volumetric solutions, by neutralizing the volumetric oxalic acid with the standard alkali, and determining the oxalate salt formed by titration with the potassium permanganate solution. The only precaution here is to use a nonreducing indicator in the oxalic acid-alkali titration, so that it will have no effect on the subsequent permanganate titration. It follows that the cubic centimeters of oxalic acid are exactly equivalent to the cubic centimeters of standard alkali and of permanganate. RECEIVED August 17, 1937.
