The Bowl of Snow is one of the items that are necessary to solve the riddle in Arqua. Combining the Flask with Red Powder and the Bowl with Black Powder, the two substances serve as chemical catalysts for each other and their reaction produces Snow, which is representative of the Water element.
Adam: This is snow. The powder's changed to snow.
Being fairly inexperienced in the broad field of Chemistry, I was trying to do some research and identify the two substances that Adam and Rebecca use to make artificial snow. One of the methods I came across makes use of a chemical substance called sodium polyacrylate, as detailed by Anne Marie Helmenstine, Ph. D. in her article How to Make Fake Snow. Additionally, Steve Ritter elaborates on a number of methods for simulating snow in his article Artificial Snow. It's all not entirely satisfying, but it's a start; and if any of you out there are equipped with a greater expertise in chemistry than myself, feel free to share your enlightening theories and speculations as to the nature of these two elusive powders. For now, we cannot but discard them as merely fictional, though magical substances.