Welcome to Science Buddies! This is an interesting project idea. I think the information in this Science Buddies project will help you a lot: http://www.sciencebuddies.org/science-f ... p049.shtml
By seeing what makes ice melt, you are looking at something called a colligative property
of water. A colligative property is something that is affected by substances that are dissolved in the water. This project looks at freezing point
, which is the temperature at which ice melts. If more "things" are dissolved in water, then ice will melt at a lower temperature. This is why cities pour salt onto roads when it snows - to make the ice melt at a colder temperature, which will make the water on the road turn to liquid water instead of ice (for safer driving).
Now to get at your particular project. You are comparing beet juice to carrot juice. Both of these liquids have lots of dissolved substances in them. It does not matter whether those things are salts; the more "things" dissolved in the liquid, the greater it will affect a colligative property like freezing point. Also, a greater concentration of substances will affect a colligative property more. So you need to consider how much
"stuff" is dissolved in each juice, and at what concentration. If carrot juice has more "stuff" in it, then it will likely melt the ice faster. That "stuff" can be everything from sugar to salt.
I hope this helps. Please post again (in this same thread) if you have more questions.