and Chemical Action on a Steam- Jet. 317 



charge of electricity, the formation of larger drops would 

 be facilitated. 



I am not aware that any measurements have been made which 

 show directly the influence of electrification on the vapour- 

 pressure ; indeed, the preceding expressions for the magnitude 

 of this effect show that such measurements would be hardly 

 realizable. I think, however, that some of the effects of 

 electrification on a steam-jet which were first observed by 

 H. v. Helmholtz, and subsequently by Shelford Bidwell and 

 Aitken, may be explained by these principles. When a jet 

 of steam emerges from a nozzle into dust-free air, there is 

 \ery little condensation to be observed within half an inch or 

 so of the nozzle. If, however, an electrode from which elec- 

 tricity is escaping is placed close to the origin of the jet, 

 dense condensation occurs right up to the nozzle, the jet 

 appearing coloured, the colour apparently being due to the 

 scattering of light by a great number of very small particles 

 of water, the diameter of the particles being very small com- 

 pared with the wave-length of light. 



An easy method of showing the effect of electrification is to 

 produce the steam by boiling water in a flask, through the 

 cork of which a piece of glass tubing shaped like a T is 

 placed. The steam passes through the vertical portion of the 

 T, then diverges into two horizontal streams, one to the right 

 the other to the left, these emerge into the air through fine 

 nozzles. Two platinum electrodes are fused through the 

 horizontal tube, the one to the right, the other to the left 

 of its junction with the vertical tube, so that one elec- 

 trode is in the path of the jet to the right, the other in 

 that of the one to the left. These electrodes are connected 

 to the terminals of an induction-coil ; when the coil is not 

 working the jets close to the nozzles are almost invisible, but 

 as soon as the coil is turned on copious condensation occurs 

 right up to the nozzles, the jets looking brownish by trans- 

 mitted light. The condensation in the jet which has swept 

 past the negative electrode is denser than that in the one which 

 has gone past the positive. 



The considerations we have previously given of the effect 

 of electricity on the vapour-pressure are in accordance with 

 the behaviour of the jet when under the influence of elec- 

 tricity. The electricity which escapes into the gas is carried 

 by charged atoms of the gas, and since in the region imme- 

 diately around these atoms there will be a very intense electric 

 field there will be a tendency for the steam to deposit in these 

 regions. Thus around these charged atoms there will be 

 very small drops of water; these drops scatter the blue light 



