My day job requires that I can practice the art of calorimetry with some reasonable extent of expertise, so in that vein I have been cracking open some of my dusty p-chem texts and revisiting basic thermo.

The other day while on an excursion to a bricks and mortar bookstore to pick up some of my favorite periodicals (Kitplanes and Vanity Fair), I happened upon a copy Elements of Chemical Thermodynamics by Leonard K. Nash (1970, Dover, $12.95). Feeling bad for Borders and their current run of poor luck, I bought the book as though it would make some difference.

Figure 2 on p 5 (below) shows a schematic of a ice calorimeter.  An ice calorimeter uses a thermally isolated enclosed space M completely filled with liquid and solid water immersed in an insulated tank of ice and water B. The internal, thermally isolated, working volume of water has two important features- it has a small volume sample container R protruding into it and it has a calibrated small inside-diameter expansion capillary C. 

A sample in container R is in thermal contact with reservoir M.  Heat absorbed in M melts some ice and results in the loss of low density ice and the formation of higher density liquid water. The net volume of the contents then decreases and is registered as a column height change in capillary C.

Given the volume change and knowing the density and heat of fusion of water at 0 C, one can calculate the heat absorbed by the reservoir.

So, what about Saturn’s moon Enceladus? The moon is thought to be covered by water ice with liquid water underneath. It’s reasonable to assume that if some volume of water below the ice transitions to the solid phase then the collective volume for liquid water is decreased resulting in an uptick in pressure.

If this happens, it could provide a mechanism for the geyser phenomenon witnessed by the Cassini probe. The geyers could simply be a result of PV work energized by gravity and radiative cooling of the surface and subsequent thickening of the surface ice into the underlying liquid phase.

I’m sure the boys and girls at Cassini have thought of this, but since I’m not tied into the literature I have not heard anybody express it.

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