Any panpsychism building complex consciousness out of basic atoms of consciousness needs a theory of ‘mental chemistry’ explaining how this building works. This paper argues that split-brain patients show actual mental chemistry or at least give reasons for thinking it possible. The paper next develops constraints on theories of mental chemistry. It then puts forward models satisfying these constraints. The paper understands mental chemistry as a transformation consistent with conservation of consciousness rather than an aggregation perhaps followed by the creation (...) of something in addition. The paper suggests that this kind of mental chemistry alone yields a workable panpsychism. (shrink)