SPECIFIC HEAT. 817 



degrees of temperature, and require diffei^ent quantities 

 of heat when their temperature is raised by the same 

 amount. The quantity of heat necessary to raise the 

 temperature of 1 kilogramme of water through 1 degree 

 C. is chosen as the unit for measuring quantities of heat, 

 and is called a kilogramme-degree. All bodies, with 

 the exception of hydrogen and certain mixtures of 

 alcohol and water, require a smaller quantity of heat 

 than water for raising 1 kilogramme of their sub- 

 stance 1 degree. The number of kilogramme-degrees, 

 or the fraction of a kilogramme-degree required for 

 raising the temperature of 1 kilogramme of a substance 

 through 1 degree is called the specific heat of the sub- 

 stance ; or, more generally, the specific heat of a body 

 is the quantity of heat required for raising its tempera- 

 ture through a given range of temperature compared with 

 the quantity of heat which would be required to raise the 

 temperature of the same weight of water to the same extent. 

 The specific heat of water is thus = 1 ; that of hydrogen 

 is = 3'4; that of nearly all other substances is less than 

 unity. 



The metal balls are made with the help of a bnllet-monld, into 

 which the iron wire is placed before the molten metal is poured in. 

 The end of the wire is previously bent into a small loop which 

 fixes it in the ball ; its projecting portion should be about 10 cm long. 

 The small projecting quantity of metal which fills the opening of 

 the mould should be left, as the wire might be cut in attempting to 

 remove it ; but any other adhering portions produced by the over- 

 flowing of the metal when it is poured in should be cut away with 

 a knife or the pincers. For heating the bullets a pot nearly 

 full of boiling water is used, small enough to allow the wires to 

 project sufficiently for seizing them conveniently with the fingers. 

 The adhering drops of water should be thrown off by a suitable 

 quick motion of the hand, before placing the bullets upon the cake. 

 This should be done quickly, and, to prevent their gliding or rolling 



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