Thought experiments in the history of science display a striking asymmetry between chemistry and physics, namely that chemistry seems to lack well-known examples, whereas physics presents many famous examples. This asymmetry, I argue, is not independent data concerning the chemistry/physics distinction. The laws of chemistry such as the periodic table are incurably special, in that they make testable predictions only for a very restricted range of physical conditions in the universe which are necessarily conditioned by the contingences of chemical investigation. (...) The argument depends on how ‚thought experiment’ is construed. Here, several recent accounts of thought experiments are surveyed to help formulate what I call ‚crucial’ thought experiments. These have a historical role in helping to judge between hypotheses in physics, but are not helpful in chemistry past or present. (shrink)