The early alchemists used to do an experiment in which water was boiled for several days in a sealed glass container. Eventually, some solid residue would appear in the bottom of the flask, which was interpreted to mean that some of the water in the flask had been converted into "earth." When Lavoisier repeated this experiment, he found that the water weighed the same before and after heating, and the mass of the flask plus the solid residue equaled the original mass of the flask. Were the alchemists correct?

Since the sealed glass container is isolated (closed system) no escape of boiled water (steam) was presented, so it is obvious that the alchemists were wrong, it is impossible that the water turns into "earth" because it has components that water does not have by itself (metallic and nonmetallic ions and molecular compounds) that is why the solid residue could have come from suspended solids or simply solids that were initially dissolved and due to the boiling of water, they remained at the bottom of the flask. Nevertheless, the experiment done by Lavoisier was more precise because the conclusion based on the initial and final masses, accounts for the boiling process; besides, the mass agreement substantiates that no mass was removed due to the isolation of the flask.

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