Cell, amalgam constant

At the heart of the model are the heat and mass balance equations governing the chlorine gas, brine and amalgam layers within the cell as illustrated by Fig. 20.3. At a more detailed level each cell is divided into eight zones. Conditions within each zone are assumed to be constant and there is a trade-off between model accuracy and execution time associated with the number of zones. Typically eight zones have been found to be a good compromise. 

The potentials are measured for a series of cells in which X2 is varied and X2 is held constant. A typical series of data for lead amalgam is shown in Table 17.1. 

Figure 17.9. Extrapolation of cell potential data from Table 17.1 to obtain a constant to calculate activities of lead in lead amalgams.

All species are aqueous unless otherwise indicated. The reference state for amalgams is an infinitely dilute solution of the element in Hg. The temperature coefficient, dE°/dT, allows us to calculate the standard potential, E°(T), at temperature T E°(T) — Ec + (dE°/dT)AT. where A T is T — 298.15 K. Note the units mVIK for dE°ldT. Once you know E° for a net cell reaction at temperature T, you can find the equilibrium constant, K, for the reaction from the formula K — lOnFE°,RTln w, where n is the number of electrons in each half-reaction, F is the Faraday constant, and R is the gas constant. 

An important and versatile parameter in the operational equation is x this constant incorporates the intrinsic efficacy of the agonist (a property of the molecule) and elements describing the efficiency of the tissue as it converts agonist-derived stimulus into tissue response (receptor density and Ke, the constant relating receptor activation and cellular response). The magnitude of Ke is also unique for each tissue since it is an amalgam of the series of biochemical reactions unique to the cell. 

A low vertical cylinder closed off with a rubber stopper serves as the electrolysis vessel and contains the sulfate solution. The anode is a piece of Pt sheet immersed in a clay cell filled with 20% H3SO4. The cell is partially immersed in the Ti (TV) sulfate solution and is surrounded by four amalgamated lead strips, also immersed in the solution. The stopper on the outer electrolysis vessel has holes for the clay cell and for the inlet and outlet gas tubes. The electrolysis is carried out in a constant stream of COg and with efficient water cooling. The current density is 0.06 amp./cm. at 24 v. for the first six hours, then 0.33 amp./cm. at the same voltage for an additional six hours. This reduces all the Ti (IV) sulfate to Ti (III) sulfate the latter precipitates as an H3804-containing hydrate (fine, pale light violet crystals). 

Weston cadmium cell A standard cell that produces a constant e.m.f. of 1.0186 volts at 20°C. It consists of an H-shaped glass vessel containing a negative cadmium-mercury amalgam electrode in one leg and a positive mercury electrode in the other. The electrolyte - saturated cadmium sulfate solution - fills the horizontal bar of the vessel to connect the two electrodes. The e.m.f. of the cell varies very little with temperature, being given by the equation = 1.0186 - 0.000 037 (T - 293), where T is the thermodynamic temperature. 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

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