A polymer, sodium alginate, reacts with calcium chloride to produce calcium alginate. Calcium alginate is a gel that is not soluble in water. A new branch of cooking, called molecular gastronomy, uses this technique to trap flavor sauces in gels to put over food. Not familiar with molecular gastronomy? Lifehacker has a good set of simple videos on the subject. You can order the kit that I used from Educational Innovations.