The idea that the extension of a chemical substance is fixed by determining what stands in the relation of being the same substance to a paradigm sample plays a substantial role in chemistry, and procedures of identification which don’t make direct use of the method can be traced back to ones that do. But paradigm samples are not typically selected by ostension, as in Putnam’s version of this procedure. The relevance of ostension is questioned after a discussion of the establishment of paradigm specimens in the analysis of some contents of crude oil and an examination of the general features of the same substance relation which takes into account the temporal dependency.