Use a cup, put the vinegar in it, and then put the eggs in it. Of course, you can get hydrochloric acid. Sulfuric acid and the like will save time for dissolving eggshells, but safety is the first priority. Never touch those strong acids with your hands. Because the membrane outside protein will not react with acid, there will be membrane in the end. Eggshells mainly contain CaCO3. The product of the reaction with acid will dissolve in the liquid.