100 Phenomena connected with the Boiling of Liquids, 



contained in this and my former paper, that, notwithstanding 

 the elaborate attack of M. Gernez, the statements laid by me 

 before the Royal Society in 1869 are confirmed. It is proved, 1 

 think : — that there are such things as nuclei which act powerfully 

 in separating vapour from water and other liquids at, or near, or 

 above the boiling-point ; that although air may assist the pro- 

 cess of ebullition, air is not by any means the only nucleus, as 

 M. Gernez affirms, but that various bodies which are not wetted 

 by the liquid, but to which vapour will adhere, act as nuclei; 

 that porous bodies such as charcoal, and especially the cocoanut- 

 shell variety of it, are energetic in absorbing vapour, and dis- 

 charging it under the action of the high temperature to which 

 they are exposed ; that the air of a room being full of particles 

 of dust and motes, the momentary exposure of a clean surface 

 is sufficient to enable it to pick up nuclei which act with 

 energy in the boiling liquid ; that the supposed inactivity of po- 

 rous nuclei does not arise from their loss of air, but from the 

 condensation of the vapours within their pores, seeing that they 

 reassume their activity under the influence of a higher tempera- 

 ture than they had been before exposed to ; that superheating is 

 not an effect of a stable or permanent character; it is not, as 

 has been supposed, the inverse effect of water cooled below its 

 freezing-point and still retaining the liquid state, seeing that 

 distillation is going on rapidly from the surface even though the 

 mass of liquid be tranquil and many degrees above its boiling- 

 point ; that the temperature of the superheated liquid is always 

 far below that of the bath, which is purposely raised much above 

 the boiling-point of the liquid under examination ; and that the 

 statements respecting water and other liquids under ordinary 

 pressure, or under no pressure at all, that they are capable of 

 attaining a temperature in some cases more than double that of 

 their boiling-points, is altogether a mistake, seeing that evapo- 

 ration opposes a limit in one direction, and the increasing ten- 

 sion of the vapour a limit in another direction to the attainment 

 of any such exalted temperature; that, in short, no statements 

 as to the temperature of the superheated liquid can be correctly 

 inferred from the temperature of the bath, the reading of a ther- 

 mometer in the liquid itself being the only reliable evidence. 



Highgate, N. July 3, 1875 



