Skey. — Oil as a Xucleus in Super-saturated Saline Solutions. 40? 



Art. LXIII. — On the Mode in ivhich Oil acts as a Nucleus in Super-saturated 

 Saline Solutions ; with Notes on the Mode of Action of Solid Nuclei. By 

 William Skey, Analyst to the Geological Survey Department. 

 [Read before the Wellingto7i Philosophical Society, 21st February, 1880.] 

 In a paper read before the Koyal Society of England "On a relation 

 between the Surface Tension of Liquids and the Super- saturation of Saline 

 Solutions," by Charles Tomlinson and G. Van der Mensbrugghe,* it is 

 stated that certain oils, both volatile and fixed, when apjplied to any of these 

 solutions, " act as powerful nuclei ;" that is, they cause the solidification of 

 these solutions, by determining a crystallization of a portion of the salt 

 thereof, which, when started even on the most minute scale, progresses 

 sometimes slowly, sometimes at a speed giving an appearance of instanta- 

 neous effect, until the whole of the solution has solidified ; a phenomenon 

 which, I may remark, is of a somewhat striking character when witnessed 

 and considered upon. 



This phenomenon is held by these investigators to be explained upon 

 the theory, which they propound, " that whatever tends greatly to lower 

 the surface-tension of a super-saturated saline solution, causes a separation 

 of salt, and at once puts an end to the condition of super- saturation." The 

 theory is backed by formulae, by frequent determination of tensions, and 

 by experimental results of a very solid and varied character. But there 

 are other results of theirs which do not appear in accordance with it, and 

 the endeavours made to show them to be otherwise have the effect only 

 of rendering this apparent unconformity the more conspicuous to me, and, 

 besides that, of creating towards the theory itself a feeling unfavourable for 

 its reception. 



It was under such an impression as to the insufficiency of the tension 

 theory to account for all the facts given in their paper that, for a better 

 understanding of the matter, I referred back to an investigation of mine, 

 communicated to you last year ; and by this I feel strongly persuaded that 

 a factor in the problem — why oils sometimes act as nuclei ? — has been left 

 out of it — and a factor of such high value, as to reduce the part which ten- 

 sion plays therein (if, indeed, played at all) to one of a very subordinate 

 character,. This factor which I would bring to your notice is that of 

 chemical affinity, — the affinity of one or more constituents of the oil used 

 as the nucleus for the water of whatever solution is operated with. 



In the communication referred to " On the Natm*e and Cause of Tom- 

 linson's Cohesion Figures,"! you may remember I stated the constitution 

 of these figures to be fundamentally different from that which is assigned 



* See also London Chemical News, Vol. 25, p. 281. 

 t Trans. N.Z. Inst., Vol. XI., p. 490. 



