V O L U M E 27, NO. 1 0 , O C T O B E R 1 9 5 5 by the Committee on the A4dvanceiiientof Research of thr University of Pennsylvania. LITERATURE CITED
(1) Conrad, F. H., Hill, E. F.. and Ballman, E. A , . I n d . E I L UC.’ / , e m . ,
32, 542 (1940). (2) Cragoe, C. “Properties of Ethylene Glycol and Its Akqueous Solutions, Cooperative Fuel Research Committee of the Cooperative Research Council, Kew York, S . 1’.(Declawified 1946). (3) Curme, G. O., and Johnston, F.,“Glycols.” d.C.6. .\lonograph 114, Reinhold, S e w York, 1952. (4) Dunstan. A. E.. Z. p h g s i k . C‘hem., 51, 733 (190;).
S;,
161 1 (5) Lange, N. A., ”Handbook of Chemistry,” 6th ed., Handbook Publishers, Sandusky, Ohio, 1946. ( 0 ) Lawrie, J. W., “Glycerol and Glycols. Production, Properties, and Analyses,” A.C.S. Monograph 44, Chemical Catalog Co., New York, 1928. (7) hIacBeth, G., and Thoinpsnii, - 4 . I ? . , ANAL.CHEY..23, 618 f1951).
(8) Ib;d.:24, 1066 (1952). (9) Romstatt, G., Industrie chinziptie, 22, 648 (1935). (10) Schierholtz, 0. J.. and Staples. 11. L.. J . Am. Cheni. Soc.. 57, 2709 (1935). (11) Spangler, J. A,, and Davies, E . C. H . , 1x11. EM+.CHEM.,.\SAL. ED.. 15, 96 (1943). RECEIVEDfor rrriew Frhriiary 8. 1955. .4cwpted .lune 3. 1955
Determination of Halogen in Organic Compounds Potentiometric Microtitration with Silver-Amalgamated Silver Electrode System EVERETT C. COGBILL and J. JACK KIRKLAND’ D e p a r t m e n t o f Chemistry, University o f Virginia, Charlottesville, V a .
‘I‘he p o t e n t i o n i c t r i c titration of halide w i t h silver n i t r a t e , employ i n g the silver-anialgamated silver electrode system of Clark, has been adapted to the niicrod e t e r n i i n a t i o n of chlorine, bromine, and iodine in org a n i c compounds. This electrode sj stem lends itself w i t h a d v a n t a g e to micro work, because it is easj to cons t r u c t , c a n be made very small in size, and gives a sensit l \ e indication of the end point even in t i t r a t i o n s w i t h v e r y d i l u t e solutions. Procedures are given w h i c h provide a c o n v e n i e n t and rapid analysis of o r g a n i c conip o u n d s on a micro scale, w h e r e 1 to 4 mg. of s a m p l e are abailable. If the substance contains ionizable halogen, it may be titrated directly in alcoholic solution; compounds w i t h nonionic halogen are decomposed most conveniently prior to the titration b y the c a t a l y t i c d r y combustion method. The procedures descrihctl have been applied to the determination of halogen i n standard o r g a n i c substances w i t h a precision of 3 parts per thousand I
T
HE direct determination of halogen in organic conipouride
invariably involves the measurement of halide ion, usualll. after preliminary decomposition of the organic subst’ance. Thr, determination of halide on a micro scale by gravimetric means ie a tedious and lengthy procedure, and hence t’itrimet,ricmethods are preferred for routine analysis. Of the volumetric nicthodq for the determination of halide, those employing visual indicators s u f f ~ from r a lack of end point sharpness, because of the high dilution of the sample and titrant which must necessarily be The potentiometric titration of chloride, bromide, and i with silver nitrate is, however, applicable to very di1ut.e solution^ and lends itself well to the determinations required in micronnalyticnal work. The potentiometric titration of halide with silver nitrate is comnionly carried out with a metallic silver indicat,or electrotit. and a reference electrode of the conventional type, such as silversilver chloride or calomel, which is connected to the titration cel! by a halogen-free salt bridge. For the titration of halide on :I niicroanalytjical scale, where approximately 0.5 mg. of the ion is to be measured, the volume of the solution must be kept small in order t80 minimize end-point errors due to solubility of the precipitated silver halide. Consequently, the electrodes u ~ c d must also be kept small in size. Moreover, the insertion of n 1 Present address, Experimental Station. E. I. du P o n t de Nemoiirs & Co., Inc., Wilmington, Del.
s:ilt, bridge int,o the titratioti V P I i p often iiiconvenierit rtnd iritrodures a poteutial so~v(:c’ of error in contaminating the solution with traces of halide or loss of the ion by diffusion into it,. In 1926 Clark ( 1 ) suggest,ed a bimetallic type of electrode system for the titration of chloride iyith silver nitrate, which has none of the disadvantages which makr c,lectrode pairs of the conventional kind awkward for micro work. This electrode pair consists of a plain silver elec-trodoand one oi amalgamated silver. This system was later adapted by Cunningham, Kirli, and 131ooks ( 2 , 3) to the ultramicrotitration of chloride in biological fluids. The latter authors found that in drop-scale potentiometricn t’itrntions, using a pair of tiny silver and amalgamated silvcr electrodea, microgram quantities of chloride could be deteriliitied Ivith an accuracy of about 0.5%. This silver and amalgamated silver electrode system deserves R wider application in the determination of small quantitirs of halide than it appears to have enjoyed. It is extremely sinil)lc to construct and can be made to fit any requirements of size. It gives a sensitive indication of the end point in the titration of bromide and iodide, as well as chloride. The authors have n.dapted :I modification of the procedure of Kirk arid his coworkers to the routine elementary analysis of organic
