SEPTEMBER 15, 1936
ANALYTICAL EDITION
STANDARDIZATION OF COPPERSOLUTION. Since the factor of calculation varies with the minute details of manipulation, every operator must determine a factor for himself, using a known solution of the pure sugar that he desires to determine and keeping the conditions the same as those used for the determination. Standardize the solution for invert sugar as follows: Dissolve 4.75 grams of pure sucrose in 75 cc. of water, add 10 cc. of dilute hydrochloric acid (sp. gr. 1.1029 at 20" C.), and invert as directed in the analytical procedure. After inversion neutralize the acid with sodium hydroxide solution and dilute to 1 liter. Ten cubic centimeters of this solution contain 0.050 gram of invert sugar, which should reduce 10 cc. of the modified Fehling's reagent. The strength of the copper solution should never be taken as a constant, but should be checked against the standard sugar solution. REAGENTS: Soxhlet's modification of Fehling's solution. Mix immediately before use equal volumes of copper sulfate solution and alkaline tartrate solution. Copper sulfate solution. Dissolve 34.639 grams of cuS01.5H20 in water, dilute to 500 cc., and filter through prepared asbestos. Alkaline tartrate solution. Dissolve 173 grams of Rochelle salts and 50 grams of sodium hydroxide in water. Dilute to 500 cc. Allow to stand for 2 days and filter through prepared asbestos. Dilute hydrochloric acid (sp. gr. 1.1029 at 2Oo/4O C.) contains 20.195 per cent of hydrochloric acid. Dilute sodium hydroxide. Dissolve 233.0 grams of sodium hydroxide in water and make up to 1 liter. Approximately 10 cc. of this solution will neutralize 10 cc. of the hydrochloric acid solution. Methylene blue indicator, 1 per cent water solution.
319
the consumer are vigilant in seeing that the amount of salt added stays very close to the predetermined figure. Consequently, it is necessary to waste as little time as possible in determining the amount of salt present in any given amount of eggs so that any material that is not up to specifications may be promptly reprocessed. There is as yet no A. 0. A. C. method for this work. The writers have investigated several methods and have found the procedure developed by B. Harris of the Emulsol Corporation to be the most satisfactory. The analysis of salt yolks, prepared accurately in the laboratory, by this method gave results which checked within 0.1 per cent. Mr. Harris has kindly permitted the authors t o submit his method, which is as follows: Weigh 5 grams of sample into a 500-cc. volumetric flask containing 200 cc. of water. Make up to mark and shake thoroughly. Pipet 50 cc. of this solution into an Erlenmeyer flask, and add 10 cc. of 0.1 N silver nitrate solution with shaking. Add 10 cc. strong nitric acid and 5 cc. of a saturated solution of ferric ammonium sulfate, and titrate with 0.1 N ammonium thiocyanate solution to a permanent light brown color. One cubic centimeter of 0.1 N silver nitrate equals 0.005846 gram of 3odium chloride. Correction factor: Subtract 0.3 per cent of sodium chloride from the result.
Acknowledgment The authors wish to acknowledge the courtesy of the Ovson Egg Company in providing the necessary materials and placing its plant a t their disposal for portions of this work.
Literature Cited
Salt Method Salt yolks are extensively packed for the mayonnaise trade, since the presence of about 10 per cent of salt not only acts as a preservative but permits the egg to be thawed as a sirupy liquid, whereas a plain yolk when thawed has a gummy, semisolid consistency. Since salt a t 2 cents a pound is very much cheaper than egg yolks a t 25 cents a pound, both the packer and
(1) Assoc. Official Agr. Chem., Official and Tentative Methods, p. 358 (1930). (2) Bailey, M. I., IND. EXQ.CHEY.,Anal. Ed., 7, 388-6 (1935). (3) Lane and Eynon, J . Soc. Chem. Zed., 42, 32T (1923) RECEIVED May 9, 1936. Presented before the Division of Agricultural and Food Chemistry a t the 91st Meeting of the American Chemical Society, Kansas City, Mo., April 13 to 17, 1936
Determination of Vapors of Chlorinated Hydrocarbons in Air HENRY F. SMYTH, JR., University of Pennsylvania, Philadelphia, Pa.
I
X COKXECTION with certain physiological investigations it was necessary to determine vapor concentrations of a number of chlorinated hydrocarbons in air. Although Barreti ( I ) has recently described a simple method for esti-
weighing bottle was immersed in warm water to hasten evaporation, but otherwise no change was made from the method already described (2). The results are summarized in Table I.
OF THERMAL DECOMPOSITION METHODWITH VARIOUS CHLORINATED HYDROCARBONS TABLEI. EFFICIENCY
Compound Chloroform Cark)on tetraohloridea s-Dichloroethvlene
0
Chlorobenzene Data from Olsen e t al. ( 8 )
Calculated C1
Trials Made
89.10 53.3s 73,16 80.96 85.52 79.73 84.49 62.77 31.52
14 14 14 14 14 16 14 14 14
Range of Concentrations M g . / l . of air P. p . m. 0.073-73.6 0.063-47.8 0.051-89.5 0.066-90.7 0.073-86.2 0.066-80.1 0,062-87.3 0.069-80.7 0.054-85.0
mating trichloroethylene vapors, i t was judged best to continue with the thermal decomposition method (a),because of the apparent general applicability of this method t o all such vapors. Accordingly, checks of the thermal decomposition method were made, using eight additional chlorinated hydrocarbons. The samples were fractionally distilled, and boiling points, specific gravities, and refractive indices were checked to assure purity. For the higher concentrations of some materials, the
15-15,100 10- 7,600 13-22,580 12-16,900 11-12,700 12-14,680 9-12,700 15-17,500 12-18,500
Known .4mounts Found Range Average
%
%
97.4- 98.9 97.3-100.6 97.7- 99.6 98.0- 99.5 98.2- 99.6 98.0-100.2 97.9- 98.9 98.2-100.0 97.5- 99.2
98.6 98.7 98.5 98.7 98.8 99.0 98.3 98.9 98.0
The method without further modification is suitable for determining the vapor concentrations of a number of chlorinated hydrocarbons over a wide range of concentrations.
Literature Cited (1) Barrett, H. M., J. Ind. Hug. Toricol., 18, 341 (1936). (2) Olsen, J. C., Smyth, H. F., Jr., Ferguson, G. E., and Scheflan, L., IND.ENQ.CHEM.,Anal. Ed., 8, 260 (1936). RECEIVED July 27, 1936.
