Please advice me a liquid whose freezing point is 2-5 Celsius.
I know that the solution of salt in water can have freezing point of about -3 Celsius. I would like to know if similar liquid but with freezing point slightly above zero can be obtained.
The liquid has to be created from readily available materials, like a mixture of water and something else. It also have to be non-explosive, non-poisonous and not easy to start fire on (so it is allowed to be sent via mail).
Why I need this:
A friend of mine is going to send some sweet potatoes to me to grow (this is a new culture in my county). But we fear that it can freeze. My friend will insulate the box with polystyrene. But I doubt that insulation will be useful without having a descent amount of heat inside the box.
The idea is to put some phase-change thermal accumulator inside the insulated box, so that the inside keeps above zero for several days while the temperature outside is several degrees below zero Celsius. In case temperature outside will drop below zero, the liquid will begin to freeze and while it is freezing the temperature inside will keep at its freezing point.