528 



Mr. Charles Tomlinson on 



[Dec. 20, 



round a central pit. A similar solution of ammonia alum behaved in a 

 similar manner : an opaque white ring formed at the circumference of 

 the drop and gradually closing in on the centre, and drawing matter 

 therefrom, produced a pit-like depression. The large drop of the solu- 

 tion often displayed suddenly beneath the surface a small well-shaped 

 octahedron, and this increased in bulk until the whole solution was solid. 

 The crystal would sometimes appear while the large drop was in the act 

 of being built up ; and the solutions in the alum flasks, more frequently 

 than in the other flasks, became solid and had to be reboiled. 



Sodium acetate in drops solidified both in crystalline lines and also in 

 heaps, these varieties occurring in the same set of drops. The crystalline 

 liues originated generally in a radiant-point, and in some cases two or 

 three such points caused the needles to cross. Sometimes in the open 

 air a speck of soot or a small insect formed the radiant-point. Within 

 doors the carrying of the plate across the room caused several of the 

 drops suddenly to crystallize. It was noticed with this and other saline 

 solutions that the deformed drops crystallized first, while those that 

 formed perfect lenses with sharply cut edges remained liquid for a longer 

 time. Drawing a point across these so as to deform their shape 

 generally led to crystallization ; but when a tail thus formed sprang back 

 again and the drop recovered its form there was no crystallization. In 

 general when a point was drawn through a drop, crystallization set in 

 where the point made its exit. Oil of almonds smeared over a plate 

 and polished with the pad of the hand was eminently nuclear. 



These experiments with drops were conducted during the week of fine 

 weather commencing on the 26th of June of the present year. I had 

 often noticed during many years past, while conducting experiments on 

 the cohesion figures of liquids, the motions of camphor, creosote, &c. on 

 water and on surface-tension generally, that the phenomena varied 

 greatly from day to day. On dull moist days drops spread out into 

 films sluggishly or not at all ; camphor, creosote, &c. would be more 

 or less inert ; in short, all surface-tension phenomena would be in a 

 depressed state. Whereas on bright sunshiny days, \vith a brisk dry air, 

 although the temperature might not be high, some force seemed to be 

 present which exalts all the phenomena of surface-tension. It may be 

 the evaporative force or the crystalline force ; but whatever it is it has a 

 powerful influence on the phenomena of super saturation. As already 

 noticed, the solutions in the flasks frequently became solid, and the drop 

 at the end of the dropping-tube could not be delivered on account of its 

 solidifying. The drops on various surfaces formed well-shaped lenses, 

 and anything that tended to destroy their symmetry led to crystallization. 

 These facts bear affirmatively on the details already laid before the Society 

 by Prof. Yan der Mensbrugghe and myself on the connexion between 

 the surface-tension of liquids and supersaturation *. Although the con- 

 * Proc. Eoy. Soc. xx, p. 342. 



