1803,1830

Platinum pyrometer

• Louis-Bernard Guyton de Morveau
• realized that thermal expansion of a metal
• could provide an alternative to Wedgwood’s
• method of determining high temperatures,
• and Guyton had worked with platinum for years.
• He placed a bar of platinum in a small ceramic trough
• open at one end and closed on the other,
• and he fixed this on a platinum plate
• so that the platinum bar pressed the short arm
• of a small platinum lever whose longer arm
• moved across a scaled platinum arc.
• *
• Guyton calibrated his platinum pyrometer
• with a mercury thermometer at low temperatures
• and compared Wedgwood’s pyrometer
• at higher temperatures. Although he showed
• that Wedgwood’s readings were too high,
• he concluded that Wedgwood’s pyrometer
• was more practical. Guyton’s delicate
• platinum spring and lever likely bent and fused
• at temperatures above the melting point of antimony.
• *
• In 1830, John Frederic Daniell improved
• Guyton’s pyrometer by separating the heated parts,
• placing the expanding bar in a cylinder of graphite.
• After removing these from immersion in molten metals,
• he clipped a lever and dial on them to measure
• the thermal expansion of the bar.

Daniell’s Register-Pyrometer

• On a new Register-Pyrometer,
• for measuring the Expansions of Solids,
• and determining the higher Degrees
• of Temperature upon the common
• thermometric scale
• by J. Frederic Daniell, Esq., F.R.S.

Practical problems

• The main trouble was the darned metal got soft.
• Also, like Wedgwood’s scale, it could be calibrated
• only at low temperatures. Well,
• practical problems typically accompany any attempt
• to venture into an unexplored space.
• One reason for ignorance—it ain’t easy, even though
• the promise of knowledge leads many to risk failure.