To show that water has a maximum density at 4ºC. Consists of a sheet metal cylinder, with two tubes in the upper and lower regions for inserting thermometers through rubber stoppers. Mounted on a base and encircled midway by an outer trough for holding a mixture of ice and salt. Temperature of the water is measured at the top and bottom of the inner cylindrical vessel over a period as the water cools. Supplied without the thermometer.