Hugh Carmichael and the Ultramicrobalance

Hugh Carmichael began to work on instruments using quartz fibres and in 1949 two quartz ultramicrobalances were constructed under his direction. Their sensitivity (10-8 gram) was practically constant up to a maximum load of 0.6 gram, and was far superior to any other balance made to that time.

The ultramicrobalance has an all-quartz beam suspended by quartz torsion fibres in a massive, airtight metal housing and the scale pans are suspended from the beam by vertical quartz fibres. All joints of the balance beam were made by fusing the quartz so that the perfectly elastic twisting and bending of quartz fibres replaced the knife-edge movements of a conventional balance.

When a sample was placed on one pan, the beam naturally lowered on that end. But instead of balancing the pans by adding known weight to the other side of the beam, the beam was brought to balance by twisting a quartz fibre attached to the beam. The amount of twist was measured by means of a graduated circle. Angle of twist could be converted to weight due to earlier calibrations of the instrument using known weights.

The graduated circle reads to one forty-thousandth of a revolution and is permitted to make six complete revolutions, corresponding to about two milligrams added on one side. The gross load including scale pans is limited to one-third of a gram on each side.
Canadian Heritage Information Network
Canadian Heritage Information Network, Canada Museum of Science and Technology, Musée de la civilisation, Stewart Museum, Canadian Medical Hall of Fame, Museum of Health Care at Kingston, University Health Network Artifact Collection, University of Toronto Museum of Scientific Instruments, University of Toronto Museum Studies Program, Suzanne Board, Dr. Randall C. Brooks, Sylvie Toupin, Ana-Laura Baz, Jean-François Gauvin, Betsy Little, Paola Poletto, Dr. James Low, David Kasserra, Kathryn Rumbold, David Pantalony, Dr. Thierry Ruddel, Kim Svendsen

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