Use of a calibrated calorimeter to measure the specific heat capacity of a substance
A sample of the material whose specific heat capacity is required, e.g., a piece of zinc, is suspended by a thread and placed in a beaker or mug of water kept boiling gently by a bunsen burner. While the temperature of the sample is being raised to 100°C, the previously calibrated calorimeter is prepared by adding exactly the same mass of cold water as before.
When the sample has been in the boiling water long enough to reach 100°C, the temperature of the cold water is noted, and the hot sample is lifted by the thread and transferred to the calorimeter. To enable this to be done with as little loss of heat as possible, the calorimeter in its jacket is held fairly close to the hot bath and the zinc transferred quickly, but without splashing. Just before transfer, the zinc is given a slight shake to remove adhering hot water. The calorimeter cover is put on, the mixture is well stirred and the final steady temperature read from the thermometer. The zinc sample may be weighed either before or after the experiment. The results of an experiment are given below to show how the specific heat capacity is calculated.
(1) The result is affected, of course, by errors inherent in the experiment, such as the inevitable small loss of heat in transferring the hot zinc to the calorimeter together with losses from the calorimeter itself.
(2) The method is of interest in that, broadly speaking, it illustrates the principle of calibration of the fuel calorimeter. In order to find the heat of combustion of various fuels, a small weighed sample is placed in a platinum crucible contained in a stainless steel “bomb” containing oxygen under high pressure. The bomb is immersed in water in a calorimeter and the fuel ignited by an electrically heated platinum wire.
The calorimeter, water, and bomb without fuel are calibrated electrically by a separate experiment to find their total heat capacity, C in J jK. Having thus measured C, the heat of combustion of the fuel sample is calculated from C () where e is the easured rise in temperature in K.