Determination of acidity of oils and fats by the quinhydrone electrode in non-aqueous solutions

Abstract

METHOD of determining the acid numbers of mineral oils by electrometric titration in amyl alcohol solu-A tions has been described by Seltz and McKinney f2). Quinhydrone electrodes were used with the reference aolution joined by an agar-agar bridge. The objection to this method is the inconvenience of preparing the reference electrodes which must be replaced frequently. A method which overcomes this difficulty is described in this article. It has been found that a silver-silver chloride electrode functions satisfactorily as a reference electrode and can be used for numerous titrations without deterioration. Furthermore, the method Jyas found to be applicable not only to mineral oils but also to vegetable and animal oils and fats. -0.2 I i -0 1 0 0 --i -0 1 -0 . 2 2 3 cc. for curves -4 , E , G, H 9 11 13 15 17 cc. for curves 0 2 B, C, D , F Figure 1Butyl alcohol seems to be somewhat more satisfactory than amyl alcohol as a solvent medium and waq used throughout the investigation here reported. Reference ElectrodeThe silver-silver chloride electrode m s of the type described by Koyes and Ellis (1). -4 platinum spiral was sealed into a glass tube and electrical connection was made with mercury. A thin layer of silver n-as electroplated on the platinum from a potassium silver cyanide solution and the spiral was then covered with a pasty ball of moist silver oxide and dried a t 100' C. in an oven. Three or four appli-1 Received J u n e 7 , 1929 cations of the oxide, with subsequent drying, were necessary to cover the spiral completely. The electrode was then heated for an hour a t 450" C. to coiivert the oxide to metal, and finally a thin layer of silver chloride was formed on the surface by electrolysis in dilute hydrochloric acid. This electrode replaced directly the quinhydrone reference electrode described in the previous publication ( 2 ) in which details of the apparatus are shown. The total cell reaction with this combination is probably represented by the equation Quinone Hydroquinone and the electromotive force (at 25' C.) of the cell is given by the equation CfiHaO, + 2 H C + 2C1-+ 2Xgo F* C~H~O ? H Z f 2AgC1 E = E " + -O.Oj91 (Quinone) X i H + ) * X (CI-)? 2 log (Hydroquinone:As (quinone) = (hydroquinone) and (Cl-) rerri:iin? practically constant, it is seen that the electromotive force of the cell during a titration is determined 11y the concentration of Hion in the solution. That this is correct is shown by the forms of the titration curves, which give evcellent inflwtions a t the end points. Figure 2 ProcedureThe procedure is similar to that described in the previous publication ( 2 ) . The solvent was prepared by saturating n-butyl alcohol (Eastman Kodak) with lithium chloride.

EMF and Voltammetric Measurements on the U(IV)/U(III) Couple in Molten LiF-BeF[sub 2]-ZrF[sub 4]

“…The instrumentation employed and the Ni/Ni(II) reference electrode in boron nitride Vol. I16,No. 12 have also been described (1,8).…”

The Transport Entropy of Hydrogen Ion in the Water-Ethanol System

“…The quinhydrone electrode has been applied to many alcoholic media (9), including methanol by Ebert (10), ethanol by Larsson (11), and n-butanol by Seltz and Silverman (12). Unfortunately Larsson's reference concerning the application in ethanol media is not readily available and we were not able to consult this reference.…”

Acid-Base Titrations in Nonaqueous Solvents

“…Several authors used acetic acid or a mixture of acetic acid and other solvents (4, 32-34, 39, 56, 59, 70, 77). The alcohols have found wide use for the determination of acids and bases (10,15,38,68,69,80). Chloroform has been used (14, 32, 41, 50,51), but generally because of its specific solvent power for the system under study.…”

“…The first recognition of titrations in nonaqueous media appears to be an electrometric procedure for the determination of acidity in oils published in the Proceedings of the American Society for Testing Materials in 1925. In the following years several modifications of this procedure were reported (10, 15,65,68,69). In 1927 Hall and Conant (25) and Conant and Hall (11) published their studies on "super acids.''…”