The presence of fluorine in fossil bones was first reported in 1803 by Italian chemist Domenico Morichini, and by the 1840s scientists had determined that (a) fluorine occurs in teeth and bone; (b) the fluorine content of teeth and bones is variable; and (c) the fluorine content of fossil teeth and bone is higher than that of fresh tissues. Middleton’s article discusses the possiblity of fluorine dating: “Having lately devoted some time and attention to the analyses of bones, both recent and fossil, I trust some of the results at which I have arrived may not be unacceptable . . . I took up the subject with the view of ascertaining, if possible, the law by which fluoride of calcium becomes augmented or developed in fossil bones, as, should this be established, an important step would, I conceived, be thereby made towards the ascertainment of geological time” (p. 285). Digital facsimile from Google Books at this link.