Determination of Naphthalene in Poultry Lice Powders' D. S. BINNINGTON AND W. F. GEDDES Department of Agricultural Chemistry, University of Manitoba, Winnipeg, Canada
A method is described for the determination room temperatureovernaphthaA P H T H A L E N E is a of naphthalene in complez miztures,involving lene and calcium chloride, a procommon ingredient of cedure which is time-consumpouitry lice powder in removal of the naphthalene by steam distillation ing and s o m e w h a t inaccurate which it may be found associated with Sulfur, powdered tobacco, in the Presence of alcohol and precipitation as owing to the unstable nature of c r u d e p h e n o l o r cresol, S O naphthalene picrate. The precipitate is dethis compound. In Colman's dium fluoride, and pyrethrum, comDosed with standard alkali, the excess sf method, titration of the residual .. picric acid is not very satisfacthe base of such preparations zohilh is determined by titration with standard tory, because of the large volume being an inert mineral filler, acid, using phenolphthalein or bromothymol blue of standard picric acid required, generally talc or a s b e s t i n e . as indicator. Data are also Presented for the the fact that naphthalene picLittle information is available solubility of naphthalene picrate in water and rate must be filtered off, and regarding the quantitative dethe unsatisfactory n a t u r e of termination of naphthalene in 0.2 per cent aqueous picric acid solutions. this class of preparation. Collins the end p o i n t . B e c a u s e of the slow rate of decomposition (3) describes a method in which the naphthalene is extracted by a methylated ether fraction of the compound, the latter difficulty is still more pronounced of boiling point 27"to 33 O C. One-half the solvent is removed in Knublauch's method, in which the naphthalene picrate is by distillation and the remainder by a current of air. The titrated directly with standard alkali. residual naphthalene is dried for 2 days in a desiccator conIn developing a method for the analysis of poultry lice taining a mixture of anhydrous calcium chloride and naphtha- powders the first requisite is the separation of naphthalene lene. A direct extraction method of this kind is obviously from the bulk of the substances with which it is associated. unsuited for the analysis of mixtures containing other ether- This is most readily accomplished by steam distillation, but soluble materials and thus becomes inapplicable to the majority difficulties are encountered due to stoppage of the condenser with solidified naphthalene. A method for obviating this of such preparations. The majority of methods described in the literature are de- difficulty by the addition of alcohol was developed, employing signed specifically for the estimation of naphthalene in coal a modification of Knublauch's procedure for the determination gas and are based on conversion to the picrate, a crystalline of the naphthalene in the distillate. additive compound, CloH&eH2(NOz)aOH (m. p. 149" C.). APPARATUS For example, Colman (4) passes a known volume of the gas The ap aratus employed (Figure 1) consists of an 800-CC. through a measured amount of 0.05 N picric acid solution, renaphthalene picrateby filtration, and titrates the re- Kjeldahl Eask fitted with a steam inlet tube reaching t o the bottom and connected by a Kjeldahl spray trap to a spiral siduall picric acid with alkali, using lacmoid or phenolphthal- condenser, the exit tube of which is lengthened to dlp almost to ein a8 an indicator. Allen ( I ) quotes Knublauch's method the bottom of a 500-GO.Erlenmeyer flask used as a receiver. T h e connection t o in which the precipithis flask is made by t a t e d p i c r a t e is means of a two-hole filtered off, washed rubber stopper, the second opening leading w i t h 0.2 p e r c e n t t'o a small wash bottle aqueous picric acid, which serves as a trap. and titrated (decomSteam is generated in posed) w i t h 0.1 N a small copper boiler and superheated by alkali, using methyl passing through a orange as indicator. short coil of 0.25-inch Volumetric meth(0.6-cm.) copper tubods are much more ing heated by a small flame. satisfactory than direct weighing of the METHOD naphthalene picrate, A s ~ ~ m p weight le as the p r e c i p i t a t e to about 0.5 equjvalent must be dried a t gram of na hthalene is transferrezto the dis' S u b s e q u e n t t o the tillation flask, rinsing preparation of this manudown the neck with script, a paper by W. L. 100 cc. of 50 per cent Miller haa appeared [ J . ethyl alcohol and 15 cc. Assoc. Oflcial Agr. Chem., of dilute sulfuric acid 17, 308-13 (1934)l cover(1to 4). Seventy-five ingsome of t h e p o i n t s cubio centimeters of 95 presented, particularly the per cent ethyl alcohol volumetric method of deare placed in the ret er m i n i n g naphthalene ceiver and a few cubic FIGURE1. DIAGRAM OF APPARATUS picrate
N
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461
ANALYTICAL EDITION
462
centimeters in the trap. Distillation is conducted at a rapid rate until the total volume of the distillate reaches about 300 cc., the receiver having been previously marked at this volume. After distillation is complete, the condenser is removed and washed down with a few cubic centimeters of alcohol, the contents of the small trap are added t o the main volume in the receiver, and any separated naphthalene is dissolved by gentle warming. Preci itation is effected by pouring the distillate rapidly and wit1 constant stirring into 500 cc. of saturated aqueous picric acid solution contained in a 1000- to 1500-cc. beaker. The precipitate is flocculated by frequent stirring and cooled for several hours,rferably overnight, in a refrigerator. Filtration is accomplishe by suction on Whatman No. 4 paper in a 4-inch (lo-cm.) Buchner funnel, transfer and washing being made with the minimum amount of 0.2 per cent aqueous picric acid solution, the picrate being finally sucked as dry as possible. The paper and precipitate are then transferred to a 400-cc. beaker, any picrate adhering to the Buchner being removed with the aid of a policeman, using the minimum amount of distilled water. Twenty-five cubic centimeters of 95 per cent ethyl alcohol are then added together with a measured excess (50 cc.) of 0.1 N sodium hydroxide, and the beaker is covered with a watch glass and heated to boiling to decompose the picrate. After cooling, phenolphthalein is added and titration of the residual alkali made with 0.1 N acid. Each cubic centimeter of 0.1 N sodium hydroxide neutralized by the picric acid liberated from the naphthalene picrate is equivalent to 0.0128 gram of naphthalene.
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Superheated steam is not essential but greatly reduces condensation within the distillation flask and thereby tends to give more complete removal of the naphthalene, in addition to minimizing foaming, which is likely to occur in the presence of considerable organic matter. The sulfuric acid is added to fix any nicotine that may be present, and also to insure definite acidity, as Allen (2) states that naphthalene cannot be quantitatively distilled from an alkaline solution. It is essential that the picric acid used be of high purity. Heating to decompose the picrate must not be continued longer than necessary; otherwise darkening may result with consequent difficulty in determining the end point. For this reason alcohol is added to accelerate the decomposition by dissolving the liberated naphthalene. Either phenolphthalein or bromothymol blue may be used as indicator, the latter being titrated to a full yellow end point. The results of twenty determinations with pure naphthalene are given in Table I. The material for these tests was prepared by twice resubliming Merck's c. P. naphthalene in an all-glass apparatus. The final product was fused and powdered in an agate mortar. Samples for analysis were weighed in a stoppered weighing bottle and transferred with alcohol to the distillation flask. Ten determinations were titrated using phenolphthalein and ten using bromothymol blue. Both sets of results indicate excellent recovery.
Vol. 6, No. 6
plicate analyses of these mixtures, together with their composition, are presented in Table I1 and indicate in all cases practically 100 per cent recovery of the naphthalene present, showing that the presence of tobacco, sulfur, cresol, and sodium fluoride does not interfere with the successful application of the method. TABLE11. ANALYSISOF SYNTHETIC MIXTURES MIX-
COMPOSITION OF MIXTURE Grams Naphthalene 10.095,sulfur 20.0, t 0bacco 40.0 talc 130 0 Naphthalen: 20.053,sulfur 20.0, tobacoo 40.0,talc 120.0 Naphthalene 40.000,sulfur 20.0, tobacco 40.0 talc 100 0 Naphthalene' 20.000,sulfur 20.0 tobacco 40.0,cresol 1.0 talc 119.i) Naphthalene 20.000, shfur 20.0, 8 0 dium fluoride 50.0,talc 110.0
TURD
NAPHTHAL~NE Found Present A B Mean Grams Grams Grams Grams 5.04
5.00
10.02
4.97
4.99
9.99 10.02 10.01
20.00 20.04 20.10 20.07 9.91
10.00
10.00 10.04
9.99
9.95
9.96 10.00
SOLUBILITY OF NAPHTHALENE PICRATE Obviously, the validity of the method is dependent on the removal of excess picric acid when washing the precipitated picrate, without a t the same time dissolving the picrate itself. Jorissen and Rutten (6) state that naphthalene picrate tends to decompose on boiling a dilute aqueous solution. They give the solubility of the picrate in saturated aqueous picric acid as 3 mg. per 100 cc. of solution a t 25" C. No data appear to be available regarding the relative solubility of the picrate in water and 0.2 per cent aqueous picric acid a t ordinary temperatures. Solubility determinations were accordingly made using these solvents : Two wide-mouth bottles were fitted with water-sealed stirrers and sintered Pyrex glass immersion filters. Approximately 300 cc. of solvent were placed in each bottle, excess freshly prepared naphthalene picrate was added, and the whole apparatus immersed in a thermostat maintained at 25" * 0.1" C., and stirred for 2 to 3 days. Samples for analysis were removed by suction. The content of picrate was determined by pipetting out a 100-cc. aliquot, adding a measured excess of 0.1 N sodium hydroxide, heating to decompose the picrate, and titrating the residual alkali with 0.1 N acid. Duplicate determinations were made on each solution and Bureau of Standards glassware was used throughout. The data obtained are presented in Tables I11 and N. TABLE111. SOLUBILITY OF NAPHTHALENE PICRATE IN WATER AT
25" c.
NAPHTHALIND PICRATE PER 100 cc. OB No. 0.1 N NaOH 0.1 N HC1 SOLUTION cc cc Gram 0.2574 la 15.00 7.80 0.2600 lb 15,OO 7.72 0.2582 2a 16.00 8.77 0.2617 TABLEI. RESULTSON PURE NAPHTHALENE 2h 16.00 8.67 Mean solubility of naphthalene picrate in water at 25' C. = 0.259 gram PHENOLPHTHALEIN INDICATOR BROE.~OTHYYOL BLFEINDICATOR per 100 cc. of solution. Naphtha- SaphthaNaphtha- Naphthalene taken lene found Recovery lene taken lene found Recovery Gram Gram .% Gram Qram % TABLEIV. SOLUBILITY OF NAPHTHALENE PICRATE IN 0.2 PER 100.2 99.1 0.5009 0.5021 0.5050 0.6008 CENT AQUEOUS PICRIC ACID AT 25" 100.5 0.4968 0.4995 100.5 0.4866 0,4840 BLANKTITRA99.4 99.3 0.5126 0.5098 0.5160 0.5124 TION OF 1000.4851 0.4815 99.3 99.1 0.5036 0.4995 cc. 0.2% 0.1N NaOH NAPETHALION~ 0.5034 100.7 99.6 0.5072 0.4874 0.4853 PICRIC ACID NAPHTHA-PICEATD PE~R 0.4852 0,4828 99.5 99.9 0.4857 0.4853 PLns 20.00 cc. LEND PICRATE 100 cc. OF 0.4954 0.4918 99.3 100.7 0.4960 0* 4995 NO. 0.1 N NaOH 0.1 N NaOH 0 . 1 N HCl IN SOLUTION SOLUTION 100.2 99.2 0.6009 0.5021 0.4954 0.4918 101.2 0.4893 99.6 0.4813 cc. cc. cc. cc Gram 0,4894 0.4879 100.5 0.5118 99.9 0.5149 0.4897 0.4893 la 20.00 11.52 11.31 0.21 0.0075 -lb 20.00 11.52 11.20 0.32 0.0114 Mean 99.7 Mean 100.1 11.52 11.26 0.26 0.0095 2a 20.00 0 . 2~1 0.007.5 2b 20.00 11.52 11.31 . Mean Bolubility of naphthalene picrate in 0.2 per cent aqueoua picric acif It is possible that certain other constituents of commercial at 25' C. = 0.009 gram per 100 cc. of solution.
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c.
.,
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lice powders may affect the recovery of the naphthalene present. In order to investigate this point, a series of synthetic mixtures was prepared closely duplicating commercial preparations. The ingredients were combined in a small porcelain pebble mill of the Abbe type, thus insuring fineness of division and uniformity of composition. The results of du-
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It will thus be seen that washing with 0.2 per cent aqueous picric acid solution eliminates the errors inherent in the use of water for this purpose, and if the precipitate is well sucked down and a small funnel and paper are used, no appreciable error is introduced by the adhering wash solution.
November E, 1934
I N D US T R I A L A N D E N G I N E E R I N G C H E M I S TR Y
DISCUSSION The results obtained on a series of pure samples of naphthalene, and on synthetic mixtures containing all the commonly occurring ingredients of commercial poultry lice powders, indicate a high degree of accuracy for the suggested method. These results have been substantiated by analyses of a large number of commercial samples over a period of 3 years. The method of decomposing the picrate by an excess of sodium hydroxide and back-titrating the residual alkali has been found experimentally to offer distinct advantages over the current gas practice of titrating the residual picric acid, and is definitely superior to direct titration of the picrate itself with alkali. It is believed that this method might be advantageously adapted to the determination of naphthalene in
463
coal gas and it should certainly prove satisfactory for the evaluation of commercial samples of naphthalene. ACKNOWLEDGMENT The authors wish to acknowledge the assistance of Louis Sair in performing a number of the analyses reported. LITERATURE CITED (1) -4llen’s Commercial Organic Analysis, 5th ed., Vol. 111, pp. 214-15, P. Blakiston’s Son & Co., Philadelphia, 1925. (2) Ibid., p, 222. (3) Collins, S. H., J. SOC.Chem. Ind., 37, 131R (1918). (4) Colman, H. G., Gas J., 144, 231-2 (1918). (5) Jorissen, W. P., and Rutten, J., Chem. Weebblad, 6, 261-72 (1909).
RJWEIVED June 27, 1934
Simple Apparatus for Photoelectric Titration W. WALKERRUSSELL AND DONALD S. LATHAM, Metcalf Laboratory, Brown University, Providence, R. I.
P
HOTOELECTRIC cells offer a means of ascertaining colorimetric end points in titration analyses which are free from subjective error. Titrations can be made by day or night, independently of lighting conditions and quite as well by a color-blind observer. Furthermore, such a method of analysis lends itself to automatic (electric) recording or control (1). Because of its ruggedness and ease of operation a photovoltaic cell was chosen for the present investigation. Hitherto (2-4) it has been found desirable to employ some type of vernier-controlled shutter, special light filters, and storage battery, or to make use of a differential method involving an additional photoelectric cell in carrying out such titrations. I n the apparatus to be described it has been found possible to dispense with all these items when using bromothymol blue as indicator. A “dead-stop” end point can be obtained accurate to better than 0.05 cc. of 0.1 N alkali, and greater accuracy is obtainable by plotting. This apparatus is largely, if not entirely, composed of items to be found in most laboratories, and is readily assembled. The potentiometric set-up which is shown on the right in Figure 1 comprised a 20-inch (50-cm.) tubular, sliding rheostat, A , having a resistance of 390 ohms, and equipped with a rack and pinion slider which made for easy manipulation. To the slider was attached a pointer, B , which allowed the position of the slider to be read on a centimeter scale held in place by means of the binding posts already on A . A second, shorter sliding rheostat, D, of similar resistance gave the apparatus a wider range, as it allowed readings t o be made upon a convenient portion of scale C. Two dry cells, E and F , furnished the potentiometer current. Two tapping keys, G and H, the former protected by the 10,000-ohm resistance I, were employed. The galvanometer, J,was of the rugged needle type, had a sensitivity of 0.3 microampere per mm., a damping resistance of 2600 ohms, and a coil resistance of 1155 ohms (Land N , type 2320-d). Although the somewhat rough potentiometer just described has been found sufficiently accurate for the present work and those of similar construction have been used in potentiometric titration (5), one of the many types of commercially made potentiometers (an L and N, student type, has been found very suitable) may well prove more convenient. The potentiometer was attached through the switch, K , to the hotovoltaic cell, L, which was a Visitron, Type F2 (manuractured by the G-M Laboratories). The cell housing, M , consisted of a wooden box, about 21 X 7 X 7inches (52.5 X 17.5 X 17.5 cm.), painted flat black on the inside. The end of the box, V , was hinged t o allow light filters to be placed in slot T between L and the titration cell, U . This cell was simply a 2-02. (60 cc.) bottle
with fairly plane, parallel sides. A portion of the light-tight cover of M was removable and notched t o allow for insertion of a small glass tube carrying carbon dioxide-free air for stirring. Through this notch was also inserted a small-bore glass tube which served t o lengthen the buret tip so that it dipped well under the solution in cell U during titration. A cardboard diaphragm, N , with a 1.75-inch (4.2-cm.) circular opening served 10 Pelts
v
FIGURE1. PHOTOELECTRIC TITRATION APPARATUS t o cut out stray light. In order to allow for focusing and variation in illumination, the small double convex lens, 0, and the light bulb, P , were mounted t o slide between Q and R. The light, P, was a 32-candlepower, 6-8 volt automobile headlight bulb which was lighted by means of current from a 6-volt transformer, 8, which was attached directly to the 110-volt lighting circuit.
METHOD The method employs the familiar Poggendorf principle of opposing the potentiometer e. m. f. to that of the photovoltaic cell and balancing by means of a galvanometer as null point instrument. The advantages of this method are well known. For the acid-alkali titrations studied, the procedure is very simple. Having in place the titration cell containing the solution to be analyzed plus 1 cc. of 0.1 per cent bromothymol blue solution, with the air stirring and the reagent buret extension tip dipped well under the solution, the bulb is lighted. The slider is now adjusted t o balance the potentiometer, and this operation is repeated after each addition from the buret. Up t o the immediate
