818 EXPERIMENTS ON SPECIFIC HEAT. 



off, the wire handles should be loosely held by the fingers. The two 

 bullets must not be placed near to each other, but several centi- 

 metres apart. 



If the bullets are made in the small mould used for previous 

 experiments, the cake should be of tallow, which is melted and 

 allowed to become cold in a small shallow round vessel, such as the 

 lid of one of the tin cases in which, some kinds of groceries are sold. 

 If the student is able to procure a larger mould, the bullets will 

 contain more heat although the temperature is the same, and a thin 

 disc of beeswax should be used for the experiment. A saucer is 

 half filled with water, and 30 grammes of white beeswax is put 

 into it. The whole is placed in a kitchen oven until the wax is 

 melted, then taken out and allowed to cool slowly without disturbing 

 it. As soon as the wax has become solid, the sharp point of a knife 

 should be led all round between the cake and the saucer, so as to 

 loosen the cake ; otherwise, as the contraction goes on, the wax 

 will show fissures, and may even be broken up into several pieces. 

 The cake should not be lifted from the water for some hours more, 

 so that it may become thoroughly hard. The cake should, if pos- 

 sible, be supported during the experiment on one of the rings of 

 the stand previously described. 



The zinc bullet produced by the small mould melts about half into 

 the cake ; the lead bullet only very slightly. If larger bullets are 

 used, the lead will still sink only very little into the cake, while the 

 zinc melts its way right through it. 



Iron has a greater specific heat than zinc, while that of bismuth 

 is still less than that of lead. A bullet of iron may be prepared 

 with some little trouble, with the help of the file, from a piece of 

 round bar iron, and a hole may be drilled through it for the wire 

 handle. The bullet of bismuth may be made in the mould. The 

 iron melts deeper into the wax, or more quickly through it, than the 

 zinc ; tne bismuth melts scarcely at all into it. 



The accurate measurement of the quantities of heat 

 received or given out by a definite body while its tem- 

 perature is respectively raised or lowered from one 

 temperature to another in other words, the determi- 

 nation of the specific heat of a body is a very laborious 

 and difficult experiment, and complicated calculations 

 are required in order to obtain very exact results. 

 The reason of this is that there exist no means of pre- 



