1885.] On the Formation of Vortex Rings by Drops. 



425 



Column of Alcohol : — 



Rings : carbon bisulphide, chloroform, water, turpentine, butylic 



alcohol, sulphuric acid. 

 Globules : olive oil, paraffin oil. 



It will be seen from the tables that a drop of one liquid only makes 

 a ring when let fall into another liquid, when the two liquids can mix, 

 and, therefore, when the surface tension is very small. 



The following experiment shows that an exceedingly small amount 

 of surface tension is sufficient to prevent the formation of the rings. 

 Absolute alcohol dropped into benzene gives rings ; water gives 

 globules : to about 10 c.c. of absolute alcohol water was added drop 

 by drop, the mixture was stirred, and a drop was let fall into ben- 

 zene. Until after the third drop of water had been added, little 

 change in the appearance was noticed ; a ring was formed, and this 

 subdivided into secondary rings, and so on. After the fourth droj> 

 was added, very small globules began to appear after a good many 

 subdivisions. After the fifth drop was added, the ring first formed 

 subdivided not into rings but into flattened globules. After the sixth 

 or seventh drop was added, the appearance of the primary ring 

 changed ; there seemed to be a more definite surface to it ; in fact a 

 small surface tension had sprung up. The globules formed on subdi- 

 vision of the ring were quite disconnected from one another, whereas 

 before there had been trails or festoons followiug each. After the 

 seventh or eighth drop of water was added, the formation of the 

 primary ring seemed uncertain ; the flattened globule, if large, broke 

 up irregularly into smaller globules without the intervention of the 

 ring shape. This experiment shows that if a liquid A forms spheres 

 when let fall into another B, then A may be diluted with more 

 than 1000 times its volume of some liquid, which has no surface ten- 

 sion with B, before it loses the property of making spheres. 



The most striking proof, however, that the formation of the rings 

 does not depend on surface tension, is the fact that the rings are 

 formed when the liquid of which the drop is made is the same in all 

 respects as that into which it falls. If we take a vessel full of water, 

 and raise from it by means of glass tubing enough water to make a 

 drop, then, when this drop falls back again into the vessel from the 

 proper height, it forms a ring. After a little practice, it is easy to 

 distinguish the ring from the rest of the liquid, and this may be done 

 still more easily if we mix some insoluble powder with the water. 



Experiments with one Liquid. 



We found on trying different liquids that they behaved very 

 differently when treated in the way we have just described. In some 

 of them a distinct ring was formed by the drop, whilst in others the 



