Ebullition of Rotating Watei 



331 



moment, a thin core of steam in the middle of the water. In 

 practice, however, water cannot be made to rotate throughout 

 its mass suddenly; and if the rotation is generated gradually, 

 the water-vapour is also, as a rule, gradually formed, and is 

 given off from the surface without ebullition, in the quantity 

 sufficient to relieve the tension of those particles of water for 

 which the pressure is diminished. The very form taken by 

 the water as it rotates, increases its surface area, and thus 

 tends to promote evaporation, and so to check ebullition. 

 For these reasons the writer has failed to exhibit the expe- 

 riment to be described in this its simplest form. If, how- 

 ever, the water is supplied with heat whilst it is rotating, 

 the steam is formed only in the region of least pressure, 

 forming a gaseous core in the rotating water, as in fig. 1. 

 The experiment is an exceedingly simple one both to make 

 and to photograph ; it may be well to give a few details 

 as to its performance, though the four figures given are 

 only careful drawings from four of the original photographs. 

 In fig. 1 the spiral wire stirrer used is seen near the surface 

 of the water : whilst beneath the wire 



gauze, on which the large beaker 



Fig. I. 



rests, and which serves to distribute 

 the heat more evenly, are visible the 

 flames and upper parts of the four 

 Bun sen burners employed to heat the 

 water. The spiral stirrer was driven 

 by a small motor ; but experience soon 

 proved that results as good, if not 

 better, could be obtained by stirring 

 the water by hand, using a long glass 

 rod completely covered by a piece of 

 indiarubber tubing in order to avoid 

 the risk of breaking the glass vessel. 

 After giving to the water throughout 

 its depth the necessary and rapid 

 rotation, and before taking the pho- 

 tographs, this rod was rapidly withdrawn from the beaker, its 

 stirring motion being carefully maintained during the act of 

 withdrawal. Some of the photographs were taken by diffused 

 daylight combined with that of the electric arc, the latter 

 being concentrated by a lens, so as to illuminate the whole 

 of the beaker and its contents as brightly as possible. The 

 plates were Edwardes's Isochromatic Instantaneous, and the 

 exposures were about the ■£$ of a second. A dilute de- 

 veloper should be used, and as much as 30 

 allowed for development. 



Thus far the experiment illustrates in an apparently simple 



lu 2 



mm. or more 



