What is magnesium sulfate? It is a fairly common industrial byproduct of the production of metallic iron. It is moderately soluble in water. One of the more interesting uses is as a source of hydrogen sulfide, which can be toxic to aquatic life. Not only is this chemical an excellent breeding ground for hydrogen sulfide, it also has the unfortunate side effect of catching fire when the container is not tightly sealed. For this reason, the production of magnesium sulfate is a highly regulated and expensive endeavor. The good news is that this chemical is not as ubiquitous as you may think. If you are lucky enough to stumble upon it in the wild, the ensuing reward is a rare and memorable occasion. The resulting brew is a fine drink.