connected with the Boiling of Liquids. 87 



the separation of vapour from boiling liquids, producing regular 

 ebullition, and preventing soubresauts, which endanger the safety 

 of the vessel if not of the operator. 



If, as M. Gernez asserts, the function of nuclei be simply that 

 of carrying down air into the liquid, that function must soon 

 become exhausted. Indeed M. Gernez attempts to show that 

 any nucleus can be exhausted, not readily it is true, but under 

 the influence of repeated boiling and reboilings separated by 

 short intervals of time. I showed in my last paper that cocoa- 

 nut-shell charcoal and some other nuclei cannot be thus ex- 

 hausted when the mode of applying heat is by means of the 

 flame of a spirit-lamp. But, it may be asked, suppose the mode 

 of heating be by means of a hot bath, what then is the effect of 

 repeated boiling? The results of experiments on this point 

 seem to me to be as remarkable as they are instructive. 



If, as M. Gernez affirms, a nucleus, such as charcoal, becomes 

 inactive after boiling five or from that to ten times in a liquid 

 at intervals of five minutes or so, the charcoal ought to show a 

 gradual decline in power, from its highest state of efficiency, 

 through advancing degrees of feebleness, to inactivity. In order 

 to test this point, wood-spirit was distilled a number of times in 

 the presence of a bit of cocoanut-shell charcoal weighing 5 

 grains; and the distillate was weighed each time after the opera- 

 tion had been conducted during five minutes. The source of 

 heat was a beaker containing 10^ ounces of water, which was 

 raised to boiling by the flame of a large spirit-lamp, after which 

 a smaller flame was kept under the beaker to prevent the tem- 

 perature from falling too much in consequence of the introduc- 

 tion of the cold vessel containing the wood-spirit, 1^ ounce of 

 which was put into a small deep-bellied retort, the beak of which 

 passed into a globular glass receiver; and this was kept wet with 

 cold water. A thermometer passing through a cork closed the 

 tubulure of the retort, while another thermometer was in the 

 water-bath. 



Water-bath containing 10J oz. of water. 

 Condenser „ 8 „ 



Wood-spirit boiling at 148° F. 1^ oz. 

 Cocoanut-shell charcoal 5 grains. 



First operation. — Bath 208°. The charcoal became active 

 when the spirit was at 90° or 100°; and it was soon dragged 

 upwards by the multitude of bubbles that issued from it. The 

 temperature of the spirit quickly attained 148°, at which it re- 

 mained until near the close of the operation. The introduc- 

 tion of the retort lowered the temperature of the bath. 



