Hello, thanks for a great mod!
One thing I found questionable (like @Chess did) was heat capacity for substances. It's halved for seawater, rendering power plants taking twice as much place for the same output, and 0 for gases -- I tend to dispose unused Nitrogen from atmospheric extractors by venting thru Steam Engine, and after adding heat capacity it even became useful, producing some spare power. Of course, it shouldn't go well for explosive gases
![Twisted Evil :twisted:](./images/smilies/icon_twisted.gif)
As for seawater itself -- I'd love to see it leaving salt in the steam engines (jamming them eventually) and water refineries, and maybe some use for that as well.