Solid-Liquid Phase Diagrams: salt solution

Trigger warning: One of the linked articles addresses tie lines.

In our summer workshops we have a demonstration (amateurishly filmed versions can be seen here and here) that is designed to show and introduce the idea of a eutectic point, the mixture of two pure substances that has the lowest possible melting point.

In the workshops, we use either a tin-bismuth or lead-bismuth mixture. The teacher campers produce 'spots' in varying alloy compositions from 100% tin to 100% bismuth. We then melt the spots on a pancake griddle and produce a eutectic graph.

All of that is explained brilliantly on this page (for the lead-tin mixture). In our summer workshop, we don't remotely address tie lines, through which the exact composition (what % of the liquid is tin versus lead) of the 'slushy' mixture can be determined. That's beyond the scope of the summer workshop, but it's highly relevant for metallurgists.

One of my campers a couple of years ago, however, brought up the connection of the bismuth-tin eutectic to the mixture of salt and water, a mixture of which melts at a lower temperature than does either pure substance. At the time, I acknowledged that this was exactly the same idea and moved on.

Since then, however, I hunted down a salt-water graph similar to that for the bismuth-tin mixture.

Lo and behold, such a graph exists, and there's even a similar article addressing how this is, indeed, like the lead-tin/bismuth-tin eutectic.

It's just the same graph as the one at the top of this article...

I'm so very happy to have found that.

Seriously...I actually am.

Why are you looking at me like that?

I'm nerdy like that.