Cromwell Mortimer, F. R. S. (
c
. 1698-1752) and the invention of the metalline thermometer for measuring high temperatures
Although the liquid-in-glass thermometer came into use either in the last decade of the sixteenth or during the early years of the seventeenth century (1), it was not until the eighteenth century that reproducible scales of temperature were established, arising from the work of Fahrenheit (2), Reaumur (3) and Celsius (4). So far as eighteenth-century chemists were concerned, the upper limit of temperature to which the liquid-in-glass thermometer could be used was set by the boiling point of mercury, at that time assumed to be 600 °F (5). In the latter half of the seventeenth century any temperatures attained in chemical operations could be indicated only by reference to a scale comprising some seven ‘degrees of heat’. In the middle to upper ranges, for example, to quote from Glaser’s The Compleat Chymist , the third ‘degree’ was that of hot ashes; the fourth ‘degree’ was that of hot sand, and the fifth that of hot iron filings; the sixth ‘degree’ was attained in the closed reverberatory charcoal fire, and the seventh and highest ‘degree’ was the ‘Flaming-Fire or Fire of Fusion’, made with wood or charcoal (6).