V O L U M E 2 4 , NO. 3, M A R C H 1 9 5 2 the absence of a blank titration. Thus a suitable reagent is one whose hydrogen ion concentration, while not facilitating a blank, ie sufficient t’o effect the reduction of peroxides within a reasonahle time. A solution of citric acid in a mixture of tert-butyl alcohol and carbon tetrachloride, which gives results in good agreement with the Lea hot and cold methods but produces no blanks, seems t o fulfill these requirements. The absence of blanks is of particular value in the analysis of fats lvith a low peroxide content. In view of the uncertainty regarding the end point in the titration with 0.002 N sodium thiosulfate, only in the total absence of iodine liberation can a fut sample be safely declared as having zero peroxide value. Precautions against atmospheric oxygen are essential for accur:tte results, regardless of the solvent used. The use of sodium iodide instead of potassium iodide, which lintl been advocated in conjunction with the acetic anhydride nit+hod (Y), and with a modified isopropyl alcohol procedure (IO) deserves a brief comment. .-ilthough both iodides give similar rewlts, sodium iodide appears preferable because of its greater solubility whether in the form of powder or aqueous solution. This applies particularly to Lea’s original hot method (S), where the presence of undissolved potassium iodide powder has given rise to doubts regarding the quantity to be used (9). Furthermore, aqueous solutions of sodium iodide have been found t o kerp longer than those of potassium iodide.
529 ACKNOWLEDGMENT
The authors are indebted to F. B. Shorland, director of the Fats Research Laboratory, Department of Scientific and Industrial Research, for permission to publish and for advice and to R. A. Chapman, Food and Drug Laboratories, Department of National Health and Welfare, Canada, for constructive criticism and suggestions. LITERATURE CITED
(1) Chapman, R . A,, and SIackay, Iioninhibits substitution and brings the empirical factor for conversion of rubber bromide to rubber hy-
drocarbon close to the theoretical factor for a completely additive product. ACK'VOU LEDGllEYT
The authors are grateful to J C. Underwood and I. C. Feustel for their.helpfu1 suggestions, t o R. V. Crook for carrying out sonie of the analyses, and to E. C. Taylor for assistanre in preparation of the figures and tables. LITERATI'RE CITED
Am. SoC. Testing Materials, Standards, Desigriatioti D 2'97-431', p. 840, 1943 Supplemelit (10443. Bloomfield, G. I.'.. J . Cheiit. Sor.., 1944, 114: Rirhhrr Ciicin. & Techno/., 1 7 , 759 (1944). Edison, T.-1..iiiipublished laboratory notes. Fisher, H. L., and Gray, .I.E.. I i d . Eng. C h e m . , 18, 411 (102G). Jones, E . P., uripublished niatiuscript. JIemk R: c'o.. Iiic., Tiahway, S . .J., J l e r c k Index, S t h ed., p. (554, 1940. Jpence. D., and ('aldwell, 51. I,.. I x n . EXG.CHb;>r., . \ N A L . ED., 5 , 371 (1933); Rubber Chenr. &- TrcImoZ.. 7, 111 (1934). IYillits, C. O., Swain, X I . L., and Ogg, C . L., IND.EXO.CHEM., AXAL ED., 18, 439 (1940); Rzrhbcr C h m . &- Technol., 20, 320 (1947). RECEIVED for r e v i r w March 2 , 1951. Accepted .January 2 , 1!)52. Presented before the Ilivision of Rubber Chemistry, .AMERIC I Y CHE\IICAL SOCIETY, Washington, D. C., February 1951.
