86 Mr. C. Tomlinson on some Phenomena 



cleanliness ; (3) the presence or absence of nuclear points in such 

 surfaces ; (4) the presence of nuclei purposely introduced into 

 the liquid ; (5) the presence of air in the liquid as diminishing 

 cohesion ; (6) the purity or impurity of the liquid as influen- 

 cing cohesion ; (7) the mode of applying heat to the vessel con- 

 taining the liquid. 



I take, for example, a specimen of wood-spirit of which the 

 boiling-point is 148° F.* In a clean test-tube over the flame 

 of a spirit-lamp, with a clean thermometer held in the axis of 

 the tube, the boiling agrees exactly with this temperature ; but 

 in a clean glass vessel plunged into a water-bath at 208°, the 

 temperature of the liquid may rise to 169° or 21° above its boil- 

 ing-point without any appearance of boiling. Distillation, 

 however, is going on from the surface, as may be shown by con- 

 ducting the experiment in a thin glass retort connected with a 

 glass condensing receiver. If the thermometer be raised out of the 

 liquid into the vapour immediately above its surface the tempe- 

 rature falls rapidly to 148°. Or if a bit of cocoanut-shell char- 

 coal weighing only 3 or 4 grains be put into the retort, the 

 liquid boils briskly at 148°, and the temperature does not rise, 

 even though the belly of the retort be plunged into water at 

 210° F. If, however, the operation be long continued, both 

 the liquid and the vapour of low-boiling fluids may become 

 slightly superheated even with a charcoal nucleus. In the ab- 

 sence of such nucleus, the superheating both of liquid and vapour 

 is considerable, as will be seen further on. 



The amount of vapour given off under the two last-named 

 conditions, namely the presence or the absence of a nucleus, 

 varies greatly. An ounce and a half of the same wood-spirit con- 

 taining a chip of cocoanut-shell charcoal weighing 4 grains, was 

 distilled during six minutes in a water-bath at 198° F. ; and the 

 weight of the distillate was 273 grains. In this case the tem- 

 perature of the liquid scarcely rose above 148° during the opera- 

 tion ; but in a second operation under the same conditions, 

 except that the charcoal was omitted, the wood-spirit quickly rose 

 to 162° or 163°, and the weight of the distillate was only 150 

 grains, or 123 grains less than in the former case, in which the 

 charcoal nucleus was present. 



Seeing, then, how powerful a nucleus cocoanut-shell charcoal is, 

 and how usefully it may be employed in facilitating the operations 

 of boiling and distilling, it is a matter as well of technological 

 as of scientific interest to determine, if possible, its function, and 

 to show the part that it really performs in facilitating so greatly 



* In Watts's Dictionary, under Methyl, Hydrate of (hi. 988), it is stated 

 that wood-spirit boils at from (>0° to G6 U> 5 C.'(140° to 151°7 F.), accord- 

 ing to the nature of the vessel, and bumps strongly during boiling. 



