244 Mr. C. Tomlinson on the Action of Solid Nuclei [Jan. 21, 



As the temperature of the water-bath fell, the ether in the tube ceased 

 to give off bubbles of vapour. A small pellet of writing-paper was now 

 thrown in : the liquid boiled up furiously, the paper being much agitated, 

 when suddenly.it sank as if dead, and all vapour-giving action ceased. It 

 had become, in fact, chemically clean. The paper was removed and a brass 

 wire passed to the bottom of the tube, when the whole liquid boiled up 

 briskly daring a few seconds ; when, the wire becoming chemically clean, 

 all action ceased, except from a point near the bottom of the wire, which 

 continued to pour off a fine stream of bubbles during some minutes. The 

 wire was now taken out and filed, in order to get rid of this nucleus. On 

 returning it to the tube the ether boiled up as before, the handling and 

 filing having made the whole immersed surface unclean ; but the ether soon 

 cleaned it, and it became inactive ; but the active point was not only not 

 got rid of, but there were now two points rapidly discharging vapour. 

 These points are probably portions of porous dross entangled with the 

 metal. During these experiments the ether was maintained at about 96°, 

 and it boiled only when a solid nucleus was introduced. 



Methylated spirit was raised to about 1 78°. A piece of flint that had 

 long been exposed to the air was put into the tube ; it gave off vapour from 

 its surface in abundance. The flint was taken out and broken, and the two 

 fragments were returned to the spirit. The newly fractured surfaces, being 

 chemically clean, were quite inactive, not a single bubble of vapour appear- 

 ing on them, while the outer surface continued to give off vapour as before. 

 A strip of slate gave off vapour from a number of points in both surfaces ; 

 it was split into two strips and replaced in the hot liquid ; the old surfaces 

 were active as before, but the fresh surfaces were perfectly inactive. Mica 

 and selenite do not answer well for these experiments. In the specimens 

 tried, air containing dust had been dragged in in patches between the 

 plates ; these, when newly split and put into soda water, showed consider- 

 able portions that were chemically clean in the midst of unclean patches. 



The action of nuclei can be well exhibited in oils with high boiling-points, 

 such as the essential oil of turpentine, rosemary, &c. When the oil is 

 boiling in a tube over a spirit-lamp, a strip of slate with one new surface 

 may be introduced before the lamp is removed, so as to prevent the oil from 

 being chilled. If, now, the lamp be taken away, vapour will pour off from 

 the unclean surface of the slate during some minutes, while the freshly 

 fractured surface will be quite inactive. 



The behaviour of nuclei, as thus far described, is the same as for super- 

 saturated saline and gaseous solutions. A chemically clean nucleus will 

 not separate either the salt or the gas from solution ; a chemically unclean 

 nucleus will do so immediately it comes in contact with the solution. 



If the definition I have given of a liquid at or near the boiling-point be 

 accepted, and it be admitted that solid nuclei behave in the same manner 

 under the same conditions in separating salt, or gas, or vapour from solu- 

 tion, what is the action in this respect of air and gases ? 



