154 



SCIENTIFIC NE^VS. 



[Sept. 1st, 1 5 



VORTEX RINGS. 



PROFESSOR THOMAS ESRICHE, of the Bilbao Insti- 

 tute, has communicated an interesting article on the 

 above subject to La Nature, and we are indebted to our con- 

 temporary for the illustrations with which this article is 

 accompanied. Professor Esriche remarks that all who have 

 learnt a little chemistry will doubtless remember the in- 

 teresting experiment of making vortex rings by letting 

 phosphoretted hydrogen (mixed with traces of another com- 

 pound of phosphorus and hydrogen) escape into the air 

 from watef . As this curious phenomenon evidently did not 



milk can be used, if drops of it are allowed to fall gently in 

 a glass of water. 



As to rings of smoke, these can easily be made by puffing 

 smoke from a cigarette through a tube, as in Fig. i. Some 

 precautions, however, are necessary to insure success ; for 

 instance, all currents ot air must be prevented. For this 

 purpose, windows and doors should be closed, and to pre- 

 vent ascending currents being produced in proximity to the 

 body of the operator, it is desirable to make the experiment 

 over a table, as shown in Fig. i ; the rings will not 

 then be appreciably affected by currents of warm air. A 

 tube two centimetres in diameter, made by rolling a 



Fig.i r. 



Fig. 2. 



Fig. 3- 



Fig. 4. 



depend on the peculiar properties of the gas, he for a long 

 time sought means of producing it with tobacco smoke, and 

 even with some chemical precipitates which are a kind of 

 smoke in liquid. After some failures he succeeded, and, 

 briefly, this was his modus operandi. 



He took a little hydrochloric acid in a pipette, and let 

 drops of it fall into a very weak solution of nitrate of mer- 

 curj'. Rings of chloride of mercury were then formed, and 

 they had a vortex movement similar to that which charac- 

 terises the rings formed on the combustion of phosphoretted 

 hydrogen. The drops of acid must fall slowly, and from a 

 point near the surface of the liquid. The same result can 

 be obtained in other solutions, provided the precipitate is 

 not too thick, as rings would not then be formed. Even 



sheet of ordinary note-paper, answers very well for 

 rings three or four centimetres in diameter at the outlet of 

 the tube. 



To observe the rings well, it is best to direct them towards 

 the darkest part of the room, or towards a black board. 

 The first puffs of smoke will not produce rings unless the 

 tube has been previously filled with smoke. The vortex 

 movement is easily seen at the outlet of the tube, and even 

 at some distance beyond it. 



As to the appearance of rings sent with more or less 

 speed to various distances, the Figs. 2, 3, and 4 give a 

 tolerably clear idea. The Figs. 5 and 6 show how the rings 

 lose their shape when the surrounding air is quiet : they 

 have the appearance of filaments of smoke falling down- 



