1879.] 



Mr. C. Tomlinson on the Action of Nuclei. 



329 



that solid bodies, boiled up with, the solution, are inactive ; and I have 

 found them to be so when put into the hot or warm solution, and left 

 till cold: and that oils and other liquids, boiled or heated with the 

 solution, become equally inactive. Several observers, who have more 

 or less recently worked on the subject before us, have not attended to 

 this condition, and hence, obtaining negative results, have declared 

 that the oils, &c, have no nuclear action under any circumstances. 



If, however, a nucleus from without be introduced into the cold 

 solution, a nucleus that is capable of adhering to the salt and not to 

 the water of the solution, a molecule of the anhydrous salt is thereby 

 set free, and in the very act of separating, ten atoms of water enter 

 into combination, and thus determine the solidification of the whole 

 of the solution in the form of the normal salt.* 



If the nucleus fail to catch one of these saline molecules, as it were 

 in the nascent state, but disperses through the solution, its effect is to 

 lessen the adhesion between the water and the salt, and a portion of 

 the seven-atom salt is liberated (mostly at the bottom of the vessel, 

 where the solution is richer in salt) provided the temperature be not 

 too high : this effect is also produced by cold alone. 



If an essential oil, which acts as a nucleus in determining the 

 formation of the normal salt, be submitted to distillation, the distillate 

 reassumes its cohesive force, and when added to the solution, is no 

 longer active, seeing that whether in the lenticular form, or dispersed 

 in globules, it has a separate existence of its own, the lens and each 

 minute globule being bound up in their own surface tension, which 

 prevents them from coming into contact with the salt. If, however, 

 the drop of oil spread out into a film upon the surface of the solution, 

 the cohesion is so far weakened that adhesion between it and the salt 

 becomes possible, separation usually takes place, and large crystals of 

 the normal salt mould themselves on the under surface of the film. 



If such be the true explanation, it is clear that any other force 

 which diminishes or destroys the cohesive force of the oil, must confer 

 upon it the same nuclear property. Consequently, a freshly distilled 

 essential oil, mineral naphtha, &c, which are inactive, become active 

 by the addition of a little absolute alcohol, ether and similar liquids 

 in which they are soluble. 



The fixed oils which tend to become rancid through age are also 

 active, and the stearine deposited by them is especially so. Newly 

 refined fixed oils, which are inactive, become active on the addition of 

 a little alkali ; but the tendency of potash, soda, and ammonia is to 



* Lowel noticed that when the transparent seren-atom salt is removed from the 

 solution, it becomes opaque and hot in consequence of the fixation of three addi- 

 tional atoms of water. In such case the supersaturated mother liquor on the 

 surface and entangled among the crystals, produces, in the absence of a nucleus, a 

 crystal of the normal salt by evaporation, and this acts as a nucleus. 



VOL. XXIX. 2 A 



