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V O L U M E 22, NO. 2, F E B R U A R Y 1 9 S O bration curve accurately. I n the second, for which the average molecular weight and deviations from ideality of the impurities vary widely, a two-solvent method is often effective in analyzing for the component of interest. The following methods of measurement of freezing point curves were discussed, including advantages and disadvantages of each: classical method in general industrial usage; constant, large teniperature differential method in use at Sational Bureau of Standards; constant, small temperature differential method in use a t Calco; and automatic equipment and platinum resistance thermumetry. Analysis of Pyrazine. .Issay and Determination of Basic Impurities. WILLIAMS ~ a i r a s J. , T. WOODS,AND WLmnrm , ilmerican Cyanamid Co. Calco Chemical Division, Bound Brook, S.J. ~
A method proposed for the dcterniination of pyrazine involves the formation of an insoluble mercuric sulfate addition compound Iiy reaction with a known volume of standard mercuric sulfate in excess. The insoluble mercury complex is filtered off and the excess mercury is determined by the Volhard method. The precision of the proposed method, expressed as the standard deviation, is *0.25% (absolute). Piperazine, diethylenetriamine, ethylenediamine, and ethanolamine do not interfere, provided t h a t the precautions suggested are followed. Coprecipitation of some of thc impurities present niay take place if the precipitant is added too rapidly or if the sample is added to the precipitant. A small correction is applied for the solubility of the mercury complex. Some indication of the amount of the above-mentioned basic impurities is obtained from a potentiometric titration of the sample with standard alkali after adding an excess of standard acid. In general two inflection points are obtained, a t about pH 4 and 8. From the volume of the standard alkali consumed to each of these breaks, and from the amount of acid added, it is possible to obtain some information in regard to the amourlt and type of basic substances which are present as impurities. The water in the sample niay be determined by means of Karl Fischer reagent in the usual manner.
Delaware Chemical Symposium HE Delaware Section of the AUERIC~X CHEMICAL SOCIETY in rcollaboration with the Universit>- of Delaware sponsored the second Delaiwre Chemical Symposium on the University of Delaw i r e campus a t Sen-ark, January 21. Section meetings were held on annlytical, organic, physical, and polymer chemistry, in addition to a program of papers on chemical development and applications research. Abstracts of the papers presente 1 before the analytical chemistry section xre printed here. Determination of Small Concentrations of Carbonyl Compounds by DiffPrential pH Method. H. R. ROE, Polychemicals Department, Du Pont Experimental Station. Aldehydes and ketones react with hydroxylamine hydrochloride forming oximes and liberating hydrochloric acid. Under selected conditions, the decrease in pH, resulting from the release of hydrochloric acid, is a direct measure of the concentration of carbonyl compounds present. A rapid routine method was dexribed which includes the calibration of a standard working curve under optimum conditions for this reaction a t carbonyl concentrations of 0.01 to 0.170, fiom which a direct quantitative determination of carbonyl can be made by simple pH measurements. The method has been found generally applicable to aldehydes and methyl ketones. The time required for a single analysis is about 5 minutes. Results are reproducible to 1 2 % relative. Polarographic Estimation of Formaldehyde. GEORGE A. CROWEA X D CECILc. LYXCH, University of Delaware. The influence of pH, temperature, and supporting electrolytes on the polarographic wave height of formaldehyde has been studied over the range of pH 8.77 to 12.7, and from 15' to 95" C. 73v the A4rrheniusequation it is possible to estimate the dehydration of formaldehyde in dilute aqueous solutions from polarographic nave height on the nssuinption that this wave height depends upon the dehydration rate of a formaldehyde hydrate at the dropping mercury electrode.
Microdetermination of Sulfur by the Grote Method. Photometric Detection of Titrimetric End Point. ROLAND N. WALTER, Hercules Experiment Station. In the Grote combustion micromethod for determining sulfur in organic compounds, t>hesulfate formed is usually titrated with standard barium chloride solution, using tetrahydroxyquinone or an alkali salt of rhodizonic acid as an internal indicator. .I photometric method of detecting the end point, which is more objective than the usual visual method, was described. Titrntion results are reproducible within 0.004 my. of sulfur. r s e of Iodine Reagents for Determination of Purity and Water Content of Xanthates and Dithiocarbamates. A. L. LINCH, Miscellaneous Intermediates rlrea Laboratory, Dn Pont Chambers Works. The reaction of iodine with salts of xanthates and dithiocarbamates to produce the disulfide derivatives by oxidation is old and familiar chemistry, but its application to the estimation of purity has encountered interferences. Best results have been obtained by conducting the iodometric titrations in alcohol a9 a solvent, and using the conventional starch solution as an outside indicator. Good agreement lvith purity derived from sulfur (Parr bomb) and nitrogen (Kjeldahl) content was attained. ripplication of the Karl Fischer reagent for moisture has furnished a method for the accurate determination of water of hydration as well as ertraneous moisture in crystalline santhates and dithiocarbamates. In view of the ease with which these derivativrs are oxidized to the disulfide in aqueous entia1 reaction of the Fischer reagent iodine L out further reaction with the sulfhydryl groups in the anhydrous system was unexpected, and indicates that the iodine may be present in the reagent as a complex rather than as a simple solution. Twenty xanthate derivatives and fourteen nitrogensubstituted dithiocarbamates were investigated in the course of this study to establish limits for these iodometric procedures. Determination of Trace Amounts of Chlorine in Organic Compounds. W m L I . i a r €1. CALKISR,Polychemicals Department, Du Pont Experimental Station. A method has been developed for the determination of trace amounts of chlorine in organic compounds with an accuracy and precision of *l 'p.p.m. in the range of 0 to 10,000 p.p.m. of chlorine. It is based on the combustion of a large sample followed by scrubbing of the off -gas and potentiometric titration of the scrubber solutions. The procedure has been shown to be applicable to adiponitrile, benzene, cyclohesane, and methanol. S o difficulty is anticipated in application to other combustible organic compounds. Solids may be analyzed by dissolving them in solvents n-hich have been so analyzed, and combust,ible gases may be analyzed iilerely i,?metering knoim amounts into the apparatus.
L.S.U. Analytical Symposium HE third annual Symposium on Modern Methods of . h a rlytical Chemiat,ry x a s held on the campus of t,he Louisiana State University, Baton Rouge, La., January 30 t o Eebruary 2 . Abstracts of papers presented are reproduced here. DEIAHAY, Louisiana State Vnivtwity, Polarography. PAL-L Baton Rouge, La. Introduction Instrumentation 1. Measurement of the diffusion current Photographic recording instruments Pen-and-ink recording instruments Manual method 2. Differential methods Method involving two dropping mercury electrodes Method involving superposition of an alternating voltage 3. Special methods for investigation of reversibility-irreversibility character of an electrode reaction Kalousek's method Oscillographic methods Recent Advances in Theory Investigation of validity of Ilkovii! equation Equation of wave for an irreversible electrode reaction Comparison of half-wave potentials with potentials calculated from thermodynamic data Limiting current controlled by reaction rate Adsorption waves
