Isopiestic Determination of Osmotic Coefficients at 100 degrees C by Means of a Simple Apparatus.

Improved apparatus and procedures for isopiestic studies at elevated temperatures

“…1. It differs from that of Grjotheim et al 4 in a number of respects relating to its construction. In particular, we have replaced their materials ͑mainly aluminum͒ used for block, chamber, and cups with more suitable metals and we have devised a more effective cup seal.…”

“…The apparatus of Grjotheim et al 4 is based on conventional isopiestic designs; the cups containing the electrolyte solutions are well seated in a metallic block to promote thermal equilibration, with the whole assembly enclosed in a metal chamber. Their apparatus features a novel method for closure of the isopiestic cups at the equilibration temperature: individual cup lids are pushed downwards by a pressure plate attached to a shaft through a vacuum-tight seal in the top of the chamber.…”

“…Consideration of the method of preparation is of importance in the calculation of the uncertainties in the initial molalities. Since our ultimate interest was in determining the water activity in aluminate solutions, which may be formally regarded as mixtures of NaOH and NaAl͑OH͒ 4 The corresponding results for the case of a solution prepared directly from the pure solutes and solvent are much simpler.…”

“…This apparatus is capable of operating at temperatures between 110 and 250°C. On the other hand, Grjotheim et al 4 have described a more traditional apparatus, designed to operate at around 100°C, in which the solution cups are sealed at the equilibration temperature, allowed to cool, and then weighed accurately with appropriate corrections for air displacement. The relative simplicity and low cost of the Grjotheim et al design are attractive, but their mechanism for sealing the cups is not entirely satisfactory, as outlined below.…”

A BET model of the thermodynamics of aqueous multicomponent solutions at extreme concentration

“…In these calculations, the small differences in solute composition {0.0034 in x * (LiNO 3 )} and temperature ( T ≈ 1.25 K) were ignored. The results are shown in figure 1, both as water activity against the water mole fraction (calculated by assuming complete dissociation of the salts), and in a form linearised according to the BET relationship in equation (17) and using the definition of x w given after equation (21). Water activities for (8) 393.36 to 393.96 0.5034 Simonson and Pitzer (8) 393.25 1.0 Braunstein and Braunstein (11) 393.25 0.5034 Braunstein and Braunstein (11) 392.15 0.4500 Tripp and Braunstein (9) 392.15 0.5000 Tripp and Braunstein (9) 392.15 0.5500 Tripp and Braunstein (9) 392.15 0.6000 Tripp and Braunstein (9) 392.15 0.6500 Tripp and Braunstein (9) 392.15 0.7000 Tripp and Braunstein (9) a The range of results listed here is only a subset of those presented by these sources.…”