connected with the Boiling of Liquids, 89 



acquired a temperature of 160°, or 12° above its boiling-point; 

 it then suddenly discharged so much vapour as to turn about 

 half the contents of the retort into the receiver. 



Eighth operation. — Similar to the seventh. The spirit rose to 

 161°, when the charcoal suddenly became active, and the spirit 

 sank to 150°. 



Ninth operation. — After five minutes with a fresh charge. 

 The charcoal burst into activity at 148°, and the distillation 

 proceeded regularly. 



Bath 196° Spirit 152° 



193 153 



Weight of distillate in five minutes 190 grains. 



The above details seem to me to throw considerable light on 

 the question at issue, namely, what is the function of such a 

 nucleus as cocoanut-shell charcoal? We have seen that in the 

 first operation a fresh piece of charcoal becomes active at 90° or 

 100° when the air contained within its pores becomes displaced 

 by the heat and by the vapour ; and it soon displays great acti- 

 vity in liberating vapour, and would continue to be active 

 during many hours, as I have often found in distilling water, 

 turpentine, and other volatile oils, as well as spirits of wine 

 and other liquids of low boiling-points. But if, when the 

 charcoal is fully active, its function of absorbing vapour and 

 liberating it under the action of heat be arrested and the 

 charcoal itself transferred to a cold liquid, there is a conden- 

 sation of vapour within its pores; so that in the second and 

 some of the subsequent operations the spirit requires to be 

 raised to the boiling-point before the vapour thus condensed 

 can be made volatile and the charcoal become active. But if 

 instead of an interval of five minutes the charcoal be left in the 

 liquid during twenty-four hours, the condensation is more com- 

 plete ; and it requires a superior temperature to that of the 

 boiling-point to vaporize the liquid within the pores of the char- 

 coal. Thus we see that in the seventh and eighth operations 

 the spirit rose 12° or 13° above its boiling-point before the 

 charcoal nucleus became active; and its activity being thus re- 

 stored, we see that in the next operation, after an interval of 

 only five minutes, it became active at 148°, as before. It seems 

 to me to be ignoring the obvious teaching of the facts before us 

 to suppose, with M. Geruez, that the charcoal becomes inactive 

 because the air has been driven out of it, when all that is wanted 

 to restore its activity is a higher temperature; and this can be 

 given either, as in the case before us, by the liquid becoming 

 superheated, or by holding the retort over the flame of a spirit- 

 lamp, which is the more expeditious way. Of course in the 



