To measure the specific latent heat of ice by direct heating
A calorimeter lagged with sheet expanded polystyrene, as described for the approximate determination of the specific latent heat of steam, is used in this experiment also. This is preferable to the use of a polished calorimeter in an outerjacket owing to the fact that water vapour from the air is liable to condense on the surface and give up unwanted latent heat.
The circuit shown in Fig. 42.4 is connected up, and the calorimeter is then weighed empty. After being lagged in the manner described it is filled with small pieces of melting ice which have been previously dried on a cloth. The immersion heater is then inserted into the ice. Some forms of heater may be themselves used as stirrers; otherwise a separate stirrer is essential. A stopclock is started and simultaneously the current is switched on. Stirring is kept up continuously, and more dried ice added as the water level sinks. As soon as all the ice has just melted the current is switched off and the time noted. Finally, the jacket is removed and the calorimeter is weighed.