804 



THE SPHEROIDAL STATE. 





mains globular and nearly motionless ; if the quan- 

 tity is larger than l cm in diameter, it takes mostly the 



form of a star, and has a quick, 

 tremulous, or sometimes rota- 

 tory, motion. 



The experiment is usually 

 designated as 4 Leidenfrost's 

 experiment,' and the state in 

 which the liquid appears under 

 these circumstances has been 

 called the spheroidal state. The 

 hot support causes a rapid 

 evaporation of the surface of 

 the liquid drop as soon as it 



FIG. 395 (A real size, B * real size}. CQm ^ ^^ the h()t metal . the 



vapour produced prevents actual contact with the hot 

 surface, and a sort of cushion of its own vapour supports 

 the liquid as long as the high temperature of the dish 

 is maintained. The temperature of the liquid in the 

 spheroidal state is always below its boiling point, and 

 the evaporation does not proceed so quickly as 

 might be expected from the high temperature of the 

 metallic surface; but as the dish is allowed to cool, 

 a point is reached in which it is not hot enough to 

 keep the water in the spheroidal state; it is accord- 

 ingly moistened by the liquid, and a violent ebullition 

 ensues. 



A copper dish is soon covered with oxide when made red hot, 

 the inside must therefore be well polished with emery paper 

 each time the experiment is to be repeated. Platinum does not 

 become oxidised, bnt is rather expensive. The dish shonld be sup- 

 ported by a wire triangle, the form of which is seen from fig. 395 B, 

 upon the ring of the boiling stand, and heated by a spirit-flame or a 



