Latent Heats of Fusion. 437 



solid and liquid substances and the exact melting-point. 

 None of these magnitudes is required in the method described 

 in the present communication. The principle o£ the method 

 used is simple. To a known weight W grms. of the solid, 

 maintained accurately at its melting-point, a measured 

 amount of heat is imparted by a wire of resistance R ohms 

 heated by a uniform current of C amperes. This heating is 

 carried out under such conditions that no transfer of heat 

 between the system and its environment is possible. If the 

 time required to bring about complete fusion under these 

 conditions is t seconds, we have without any corrections 



L = C 2 Ri/4'18 W grm. cal. per gram. 



Apparatus. 



A weighed amount of the substance was placed in an 

 inner vessel A (fig. 2), surrounded by an outer vessel B 

 containing the same substance, partly in the molten con- 

 dition and therefore at its melting-point. The outer vessel 

 itself was surrounded by a heat insulating arrangement 

 which served to prevent undue loss of heat from the bath B 

 during the course of the experiment, which would lead to 

 solidification of the material. The inner vessel A was a 

 small glass beaker, capacity 80 c.c. The outer vessel B was 

 an enamelled iron pot, capacity 750 c.c. 



The heat insulating arrangement in the earlier experiments 

 was a wooden box containing hay and cotton-wool. 



The inner vessel A was provided with a cork, cut so that 

 the solid centre provided a support for the heating coil (see 

 fig. 1). The centre piece also had two small holes to allow 



Fisr. 1. 



the passage of the copper leads of the coil. With this 

 arrangement it was possible to use the' heating coil to some 

 extent as a stirrer during the experiment. The outer rim of 

 the cork, from which the solid centre piece was suspended, 

 was cut so that a thermometer acting as a combined recorder 

 of temperature and a stirrer could be placed in the midst of 



