This thesis is concerned primarily with the characterisation and classification of the chemical elements by the Russian scientist D.I. 11endeleev (1834-1907). In connection with certain specific questions the contributions of other scientists are presented at some length in order to provide a background against which Mendeleev's work may be viewed and appraised.

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Today, the Flemish physician, alchemist and philosopher Jan Baptista Van Helmont (1579-1644) is mostly remembered as one of the founders of modern chemistry and medicine. However, Van Helmont saw himself rather differently: he firmly believed he had been called to articulate a ‘Christian Philosophy’ that would bring together Christian thought and natural philosophy in a harmonious synthesis. His ‘Christian Philosophy’ would be purged of the Aristotelian ‘heathenism’ he felt Scholasticism had been tainted with. Instead, it would convey a unitary view of God, Nature and Man that was in accord with Christian doctrine. The main purpose of this thesis is to understand how Van Helmont attempted to construct this new Christian Philosophy. The thesis will argue that the inspiration for this project lay in the medical alchemy developed by Theophrastus Paracelsus (1493-1541) following medieval precedents. Paracelsus and many of his followers expressed the view that alchemy can act as the Christian key to Nature, and therefore an alliance of alchemical philosophy and Christianity was not only possible, but natural. Van Helmont concurred with this perspective, seeking to ground his Christian Philosophy in both orthodox Christian thought and medical alchemy. His religious ideas drew chiefly upon Biblical and Patristic sources as well as on German medieval mysticism. Van Helmont sought to complement this approach with an alchemical view that emphasised the hidden presence of God in Nature, as well as the role of the alchemist in unveiling this presence in the form of powerful medicine. Indeed, in Van Helmont’s thought Christianity and alchemy were dynamically entwined to such an extent that their discourses were not clearly separate. Van Helmont firmly believed the source of all things was God, and hence both the Book of Grace and the Book of Nature had their common origin in the light of the Holy Spirit.