Latent Heats of Fusion. 439 



the centre of the rod and out at the farther end. The holes 

 were then plugged up with small pieces of ebonite, so that 

 the coil was solid and compact and there was no fear of the 

 wire short-circuiting. (See fig. 3 for section of coil,) 



The ends of the Eureka wire were soldered on to fairly 

 thick copper leads, 0*75 mm. diameter. The current was 

 provided in the earlier experiments by accumulators ; in 

 later experiments these have been replaced by current taken 

 directly from the 240 volt mains by using a large lamp 

 resistance. The current passed through a calibrated ammeter 

 and the whole circuit connected through a sliding resistance 

 and a plug key for convenience. 



Method of Experiment. 



A weighed amount of the pure dry solid in powder or 

 small pieces was placed in the inner vessel. The heating 

 coil was placed in the centre and the thermometer embedded 

 in the solid. The inner vessel was then suspended in the 

 bath, this being kept exactly at the melting-point by having 

 some unfused solid present and by keeping the whole well 

 stirred. The whole apparatus was then placed in the hay- 

 box and the spaces in the cardboard and cork lids kept 

 covered as much as possible by cotton-wool to prevent loss of 

 heat. The temperature of the solid in the inner vessel 

 gradually rose until it attained the melting-point. It was 

 allowed to remain ;it this temperature for at least 15 minutes 

 to make sure that all the solid was at the same temperature. 

 This was tested by moving the thermometer about in the 

 solid. 



The heating coil was then connected in circuit and current 

 passed through, the solid in the inner vessel being kept 

 vigorously stirred and the heating coil moved backwards 

 and forwards to ensure even heatino-. When all the solid 

 had fused the temperature began to rise; the time at this 

 stage was noted, as this corresponds with the time £, during 

 which heat is supplied for fusion of the substance. The 

 current throughout the experiment registered by the ammeter 

 was also noted. 



Results. 



I. Benzoplienone. — This was purified by recrystallization 

 from light petroleum, the resulting product was in the form 

 of white needles, M.P. 48° C. For the loan of one specimen 

 of Benzophenone we are indebted to Prof. J. N. Collie. 

 A beaker was in this case used as the outer heating vessel. 



