May 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
(1 to 5 ) . Add an excess of about 2 cc. of the silver nitrate solution, and determine the excess of silver nitrate according to the procedure described for the bomb-washing Calculate the strength of the silver nitrate solution in terms of chlorine.
ACKNOWLEDGMENT This investigation of the bomb method was made at the suggestion of A. c. Fieldner, chief engineer, Experiment Stations Division, U. S. Bureau of Mines.
191
LITERATURE CITED (1) Dunningham, A. C., J . Inst. Fuel, 5, 303 (1932). (2) Parr, S. W., a n d Wheeler, W. F., Univ. Ill. E n g . Expt. Sta., Bull. 37, 1909. (3) Wilke-Dorfurt, E., and Romersperger, H., 2. anorg. allgem. Chern., 186, 159 (1930). RECEIVEDJanuary 10, 1933. Presented before the Division of Gas and Fuel Chemistry a t the 85th Meeting of the American Chemical Society, Washington, D. C., March 26 t o 31, 1933. Published by permission of the Director, U.S. Bureau of Mines.
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Determination of Plasticizers in Organic Cellulosic Plastics J. D. RYANAND G. B. WATKINS,Libbey-Owens-Ford Glass Co., Toledo, Ohio However, for the rapid determination and identification N RECENT years where greater stability and lower flammability of plastic compositions have been sought, of plasticizers, the precipitation method as outlined beorganic esters and ethers of cellulose have replaced comes extremely burdensome. Frequently, plastic compocellulose nitrate to a considerable extent. Frequently, prac- sitions contain a mixture of plasticizers and the use of large tical workers in the field of plastics are confronted with the samples greatly aids the separation of the mixture into its analysis of these newer cellulosic compositions and the components. To separate large amounts of the plasticizer methods employed have been largely those which have proved from the plastic by the precipitation method requires large timeworthy in the realm of cellulose nitrate plastics. Many volumes of costly solvents and the operations are time-conof the methods (2) used in the analysis of pyroxylin (cellulose suming. I n order to circumvent these difficulties, the follownitrate) plastic are basically founded upon the recognition ing method of separation was devised. that the major component is unstable a t elevated temperaPROCEDURE tures. By taking advantage of the greater temperature stability of the organic derivatives of cellulose, it has been Five hundred grams of plastic material cut into small found possible greatly to expedite and simplify the analysis strips are placed in a 2-liter distilling flask equipped with of such plastics. a thermometer and the flask immersed in an oil bath almost to the side arm; or if preferred, the neck of the distilling flask TABLEI. DETERMINATION OF PLASTICIZER CONTENT OF may be wrapped with asbestos cord. A receiving flask of CELLULOSE DERIVATIVE PLASTICS 500 cc. capacity is attached to the side arm of the flask and PLASTICIZER CONTENT Present Found Difference kept cool by immersion in a freezing mixture or by other PLASTIC ANALYZED" % % % suitable means. A vacuum of 0.1 mm. of mercury is applied 41.2 40.6 0.6 Cellulose acetate, Type A to the system and the oil bath rapidly heated. The analysis 41.2 40.5 0.7 Cellulose acetate Type B 41.2 41.0 0.2 Cellulose acetate' Type C of a number of plastic compositions made from cellulose 28.6 28.3 0.3 Cellulose acetate' Type D 47.4 46.9 0.5 acetate, ethyl cellulose, benzyl cellulose, and plasticizers Cellulose acetate: Type E 33.3 32.7 0.6 Ethyl cellulose Type A of different types led to the adoption of an oil bath tempera33.3 32.9 0.4 Ethyl cellulose' Type B 13.0 12.8 0.2 Benzyl cellulose, Type A ture of 250" to 260" C. This temperature, while resulting 11.1 11.0 0.1 Benzyl cellulose, Type B in a slight charring, did not produce any appreciable amount a In order to prove that the method possesses wide applicatiqn, the $astic samples analyzed were made from dlfferent p!asticizera and different of volatile decomposition products of the cellulosic material, inds of cellulose derivative. The cellulose derivatwes varied in chemipal yet it was found sufficiently high to effect distillation of the properties (acetyl, content, ethoxy content, etc.), or physical properties (melting point, vlscoslty, etc.). high boiling plasticizers in common usage. Lower temperatures, while satisfactory if the plasticizer is not characterized Of primary significance to the plastic chemist is the de- by too high a boiling point, unnecessarily prolong the time termination of the character of the cellulose derivative and of separation. Higher temperatures produce volatile dethe amount as well as chemical nature of the plasticizer used. composition products of the cellulosic material, which, howAs in the case of lacquers ( I ) , these determinations are usually ever, are usually easily removable by the customary methods conducted by dissolving the plastic in a suitable low boiling of purification. Using an oil bath temperature of 250" to point solvent and subsequently precipitating the cellulose 260" C., a complete separation may be carried out in a few derivative by addition of a low boiling point nonsolvent for hours. When separation is completed, which is indicated the cellulose derivative which is a solvent for the plasticizer. by the fact that distillate no longer collects in the receiving The precipitated cellulose derivative is filtered, washed, and flask, the contents are redistilled in the usual way or by the dried. The filtrate is concentrated by distillation to remove method of Hickman and Sanford (3). the low boiling point solvents, leaving a still residue which constitutes the plasticizer. I n general, this method is satisDISCUSSION factory for the separation of the cellulose derivative, although Samples of ethyl cellulose, benzyl cellulose, and cellulose it is frequently necessary to employ great dilutions or repeat the precipitation to obtain the cellulose derivative in the acetate plastics were analyzed by the above procedure. The results obtained are outlined in Table I. I n all cases, the pure state.
I
ANALYTICAL EDITION
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purity of the plasticizer was determined by refractive index measurements, as well as by saponification values if the plasticizer belonged to the ester type. SUMMARY A rapid method for the separation of plasticizers from organic cellulosic plastics, described in this article, has been shown to be to cellulose, cellulose, and cellulose acetate plastics. Its accuracy, when- applied quantitatively to the determi-
Vol. 5 , No. 3
nation of plasticizer content of organic cellulosic plastics, was found satisfactory for practical purposes.
LITERATURE CITED (1) Bradley, IND. ENO.CHEM.,Anal. Ed., 3, 306 (1931). (2) Gardner, “Physical and Chemical Examination of Paints, Varnishes, and Lacquer,” 5 t h ed., pp. 491-550, 818-28, 850, Institute of P a i n t and Varnish Research, Washington, 1930. (3) Hickman and Sanford, J. Phys. Chem., 34, 637 (1980).
RECEIYBD December 19, 1932.
Preparation of Sodium Hydroxide Solutions of Low Carbonate Content by Centrifugation NELSONALLEN AND GEORGEW. Low, JR. Frick Chemical Laboratory, Princeton University, Princeton, N. J.
H
AVING had occasion to prepare sodium hydroxide solutions of low carbonate content, the use of a centrifugein connection with the oily alkali method (6) suggested itself. This method has long been used for preparing sodium hydroxide solutions and possesses the advantages of simplicity and freedom from the introduction of contaminating ions. On the other hand it has the disadvantages of extreme slowness and incomplete removal of carbonate. Clark (1) speeded up the process by filtering the alkali through paper, and Kolthoff (4) filtered it through a Jena sintered-glass crucible. Han and Chao (g), who have recently made a comprehensive study of all methods of preparing alkali free from carbonate, clarified the solution by heating in a water bath (6) and followed this by filtration through glass. Apparently no one has made use of the centrifuge for the clarification.
EXPERIMENTAL Samples of the oily alkali were prepared by dissolving 50 grams of pellet sodium hydroxide in 50 ml. of carbon dioxidefree water. After cooling, each lot was transferred to a Pyrex centrifuge tube, made from a 125-ml. Erlenmeyer flask by rounding out the base and blowing out an opening to fit a No. 2 rubber stopper. The neck of the flask was drawn off and a tube 5 cm. long and 0.8 cm. inside diameter sealed on. Centrifuging for 30 minutes a t 2200 to 2300 r. p. m. gave absolutely clear solutions with the undissolved carbonate and alkali tightly packed in the bottom. TABLE I. CARBONATE CONTENT OF ALKALI SAMPLE
TOTAL VOL. ACID AS 0.0998 N HC1
VOL.HCl FOR
M1.
M1.
cos - -
PERCENTHCI FOR
cos--
BEFORE CENTRIFUQINQ
1
273.36 270.67 306.66 276.24
1
271.28 278.37 309.36 276.33 330.64
2 3 4
2.40 2.42 2.48 2.26
0.88 0.88 0.81 0.82
.
AFTBR CENTRIFUQINQ
2 3 4
0.314 0.284 0.610 0.280 0.450
0.12 0.10 0.16 0.10 0.14 Av. 0.12
Samples of alkali were analyzed for carbonate before and after centrifuging by titration in the absence of carbon dioxide with standard hydrochloric acid. On reaching a phenolphthalein end point the titration was continued with 0.0998 N hydrochloric acid, from a microburet, to a pH of
4.2 as determined by methyl orange indicator and a buffer solution. The natural offset between the two end points for pure water was found to be 0.140 ml. and this correction was applied. Some typical data are given in Table I. DISCUSSION OF RESULTS Nan and Chao (2) secured an average value of 0.15 per cent for the hydrochloric acid used for the carbonate in their solutions, whereas the above data show a n average of 0.12 per cent for the centrifuged alkali. This clearly indicates that centrifugation gives a lower content of carbonate in the alkali with a very much smaller expenditure of time and labor. Then, too, no elaborate heating or filtering devices are needed. Forty milliliters of a 0.1124 N sodium hydroxide solution prepared by diluting the centrifuged alkali with carbon dioxide-free water required an average of 0.190 ml. of 0.0998 N hydrochloric acid to go from the phenolphthalein end point to pH 4.2. This value less 0.140 ml. (the natural offset) equals 0.050 ml., which corresponds to the carbonate content. Solutions prepared in this manner are perfectly satisfactory for all ordinary titrations. MODIFIEDTITRATION HEAD In connection with the above work the titration head recommended by Hillebrand and Lundell (3) has been modified by leading the carbon dioxide-free air stream through a tube passing through the cap by a ring seal and extending down about 8 cm. below the top of the head. This change insures that the titration flask will be completely swept out by the air stream. The head was made of very heavy Pyrex tubing and of a size to fit over a 250-ml. Erlenmeyer flask. Such a titration head makes a very rugged and useful piece of equipment, LITERATURE CITED (1) Clark, “Determination of Hydrogen Ions,” Williams and Wilkins, 1928. ENQ.CHEM.,Anal. Ed., 4, 229 (1932). (2) H a n and Chao, IND. (3) Hillebrand and Lundell, “Applied Inorganic Analysis,” p. 141, Wiley, 1929. (4) Kolthoff and Furman, “Volumetric Analysis,” Vol. 11, Wiley, 1929. (5) Pregl, 2. anal. Chem., 67, 23-7 (1925). (6) Sbrensen, Biochem. Z . , 21, 186 (1909). RECEIYED January 31, 1933.
