286 



Prof. T. Carnelley. On the 



[Jan. 6, 



mercury was run out of A by tilting up the bottle and inclining the 

 tube DE. By this means a. Torricellian vacuum was obtained from 

 A to o. DE was next brought to the vertical, and the bottle A 

 placed in the trough P. A tin bottle G without a bottom was fitted 

 with a cork, so that it might slide somewhat stiffly along DE. 



To begin with, the tin bottle was placed in the position G and filled 

 with a freezing mixture of salt and ice. Some boiled water was then 

 passed up the tube DE, sufficient to form a column at M about two 

 inches deep. The thermometer H had been previously arranged, so 

 that its bulb might be one or two inches above the surface of the 

 water M. The bottle A was next surrounded by a good quantity of a 

 freezing mixture of salt and ice, in order that any vapour given off 

 from the water at M might be condensed in A as fast as it was formed, 

 and thus the internal pressure might never be more than about 1*0 to 

 1*5 millims. When A had been sufficiently cooled, which required 

 about fifteen minutes, the tin vessel G was slid down the tube DE, 

 and its freezing mixture removed. The water at M had then solidified 

 to a mass of ice, which on heating with the flame of a Bunsen's 

 burner melted either wholly or partially, and the liquid formed began 

 at once to boil. The fusion commenced first at the bottom of the 

 column of ice, whereas the upper part fused only with difficulty, and 

 required rather a strong heat. The fusion in this case was probably 

 due to the steam evolved from the lower portions of the ice column 

 being imprisoned and unable to escape, and hence producing pressure 

 sufficient to cause fusion. 



When the greater part of the ice had been melted the tube was 

 tightly clasped by the hand, the heat of which was sufficient to produce 

 a somewhat violent ebullition. The liquid in boiling splashed up the 

 side of the tube and on to the bulb of the thermometer, where it froze 

 into a solid mass, as represented in fig. 2. By this means the ice was 

 obtained in moderately thin layers. The tube at the points indicated 

 by the arrows was then strongly heated by the flame of a Bunsen's 

 burner, with the following results : — 



The ice attached to the sides of the tube at first slightly fused, 

 because the steam evolved from the surface of the ice next the glass 

 being imprisoned between the latter and the overlying strata of ice, 

 could not escape, and hence produced pressure sufficient to cause fusion, 

 but as soon as a vent-hole had been made fusion ceased, and the whole 

 remained in the solid state, and neither the ice on the sides of the 

 tube nor that on the bulb of the thermometer could be melted, how- 

 ever great the heat applied, the ice merely volatilising without previous 

 melting. The thermometer rose to temperatures varying between 

 120° and 180° in different experiments, when the ice had either 

 wholly volatilised or had become detached from the bulb of the ther- 

 mometer. The ice attached to the latter did not partially fuse at the 



