A New Cell Design for Precision Conductimetry

Abstract

The design of a conductance cell intended for use with dilute non-aqueous solutions is described. The electrodes (bright platinum) are concentric cylinders with the lead to the outer electrode being a platinum tube which acts as an electrical shield for the lead to the inner electrode. Stray electrical paths are thus eliminated. The electrode assembly is mounted on a Teflon plug which is turned to a standard taper, so that the electrodes are interchangeable. Tests covering the resistance range 1000 <R< 50,000 ohms over the frequency range 500 </ < 5000 cycles per second show that the frequency variation is significantly less than that obtained with cells of other designs. Resistances up to 50,000 ohms can be measured with a precision of at least 0.02%. The if-/-1/» plot is nearly linear at low resistances but its curvature steadily increases with cell resistance; the curve can be accurately reproduced by a parabola. Consequently, a simple numerical extrapolation to infinite frequency can be made, using data at three frequencies equally spaced on a/-1 A scale (e.g., 5000, 1250 and 556 cycles).

The dissociation constant for potassium methylamide ion pairs in methylamine

“…at this temperature, 6.5 x 11101 L -l , and suggest again that "CI" for KNHCH, lies between 3 and 4 A.…”

“…The design of the electrode system was based on the recomnlendations of Nichol and Fuoss (6). The pair of concentric platinum cylinders (I cm diameter x 2 cm long and 2 cm diameter x 3 cm long) was mounted vertically in the conductivity cell (see Fig.…”

Electrochemical analysis section :

“…(39). Nichol and Fuoss [43] found that the simpler Eqs. (39) and (40) were inadequate to represent their data for dipping electrode designs and used this quadratic function of t ' .…”

Folic Acid Coenzymes and One‐Carbon Metabolism

“…B. FOLIC ACID COENZYMES A number of investigators (172)(173)(174)(175)(176)(177)(178)(179)(180)(181) have studied the conversion of folic acid by various in vivo and in vitro systems. In the cell-free extracts from mammalian, avian, and microbial sources, it was possible to demonstrate a requirement for: ( I ) formate, or a source of formate (eg., serine) ; and (2) a reducing agent, such as ascorbic acid or homocysteine.…”

“…The demonstration of the in vivo conversion of folic to folinic acid (172)(173)(174)(175)(176)(177)(178)(179)(180)(181)188), and the fact that Aminopterin toxicity was reversed far more effectively by folinic than by folk acid (9,188), led to the tentative identification of folinic acid as "active formate." However, it was not altogether clear how the folic acid-dependent transformations a t the oxidation level of formaldehyde fitted into the developing picture of tetrahydrofolic acid as the "coenzyme of transformylation."…”