[Enthalpy]

Some salts must shrink when losing crystallization water at heat (I mean, less hydrated salt + separate water taking less volume than the more hydrated salt). But where to find such a data, or a salt with such a property, no idea. From the densities of the salt with more or less crystal water, but searching that way takes unmanageable time.

[ME_BOG]

Do you know anything about the hydrates of Disodium Hydrogen Phosphate?

[ME_BOG]

Enthalpy, from the website www.sigmaaldrich.com I have discovered that the Heptahydrate of Disodium Hydrogen Phosphate has a density of 1.68 g/cm³ while the Dodecahydrate has a density of 1.52 g/cm³.

What does this tell me ?

Edit: I am interested in the possibility of using the Dodecahydrate because it has a melting point of approximately 35 degrees Celsius.

[Enthalpy]

Na₂HPO₄ weighs 141.96 g/mol.

Na₂HPO₄ ° 7H₂O weighs 268.07g/mol. 1mol occupies 159.57cm³.
5 additional mol of H₂O not bound with the crystal occupy 90.53cm³.
The total is 250.1cm³.

Na₂HPO₄ ° 12H₂O weighs 358.15g/mol. 1mol occupies 235.63cm³.

Separating the water increases the volume. Not the sought direction.

You could check the accuracy of the densities. I'm not sure neither that good crystals create under your conditions, especially if they don't have time.

[ME_BOG]

Ok thanks,

I still think it is worth a shot to try it out if i can get my hands on some of the material without having to pay an awful lot for it.
What I believe could potentially happen is that, instead of separating the water, the Dodecahydrate simply melts under the pressure (and I was unable to find any densities for it at different temperatures).

Another idea I recently had was to use an inorganic acid, like 85% phosphoric acid, however, I was sadly unable to find any phase diagrams or density/temperature data for it. What I also couldn't find was the hardness of it (although I assume that there is a decent chance the crystals will be hard). If anyone has any data on phosphoric acid I would appreciate you posting it.