Hope's Apparatus

   Thomas Charles Hope (1766-1844) was the Professor of Chemistry at Edinburgh University from 1795-1843. In 1805 he published a paper "Experiments and Observations upon the Contraction of Water by Heat at Low Temperatures". In it he showed that water has its maximum density at about 4°C, a fact well known to fish who congregate at the bottom of ponds in freezing weather.

   The apparatus at the left is at Kenyon College, and at the right is an example of Hope's apparatus at the University of Cincinnati.

   Hope's apparatus is a glass cylinder encircled with a trough half-way up to contain a freezing mixture. Holes in the cylinder at the top and the bottom allow thermometers to be inserted into the water to sample its temperature. After a sufficient length of time the more dense water collects at the bottom at a temperature of 4°C. 

   The reference below gives graphs of Hope's experiments (in his paper he only gave tables), plus additional experiments run by the author in 1981. 

REFERENCE: Thomas B. Greenslade, Jr., "The Maximum Density of Water", Phys. Teach., 23, 474-477 (1985)

                  Denison University                                                                                           St. Patrick's College
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