The historical development of a scientific knowledge on calcium orthophosphates (CaPO₄) from 1770-s till 1950 is described. Many forgotten and poorly known historical facts and approaches have been extracted from old publications and then they have been analyzed, systematized and reconsidered from the modern point of view. The chosen time scale starts with the earliest available studies of 1770-s (to the best of my findings, CaPO₄ had been unknown before), passes through the entire 19th century and finishes in 1950, because since then the amount of publications on CaPO₄ rapidly increases and the subject becomes too broad. Furthermore, since publications of the second half of the 20th century are easily accessible, the substantial amount of them has been already reviewed by other researchers. The reported historical findings clearly demonstrate that the substantial amount of the scientific facts and experimental approaches has been known for very many decades and, in fact, the considerable quantity of relatively recent investigations on CaPO₄ is just either a further development of the earlier studies or a rediscovery of the already forgotten knowledge.