Electricity of Steam. 461 



10. I then insulated an iron pan, twelve inches diameter and 

 two inches deep, and attached to it a pith-ball electrometer, 

 with balls three-eighths of an inch diameter, and threads five 

 inches long, and also attached to the pan a metallic wire, the 

 pointed extremity of which was placed about one-twentieth 

 of an inch distant from the point of another wire connected 

 with the ground. The iron pan was then filled with cinders, 

 very hot, from a wind-furnace, and on projecting upon them 

 a few ounces of water, steam was evolved with great rapidity, 

 and at the same moment the pith balls diverged to the di- 

 stance of an inch, and sparks passed between the metallic 

 wires. This was several times repeated. 



These experiments enable us, I conceive, to give a clear 

 explanation of the electrical phaenomena presented by steam. 

 There is no doubt whatever, as Dr. Faraday conjectures in 

 his note to Mr. Armstrong's paper in your last Number, 

 " that this evolution of electricity by vaporization is the same 

 as that already known to philosophers on a much smaller 

 scale." The electricity appears to originate at the instant of 

 vaporization, and the steam as it collects within the boiler is 

 electrified with positive electricity, the water and metallic 

 boiler being at the same time negative. In this condition the 

 electricity of both is latent, like the electricity of the two plates 

 of an excited electrophorus ; but the instant steam is suffered 

 to escape, its positive electricity, being carried off along with 

 it, and out of the influence of the equivalent quantity of ne- 

 gative electricity in the boiler, becomes free, and hence the 

 steam is electrical with positive electricity. The same thing 

 takes place with the boiler, in which negative electricity is set 

 at liberty as the steam escapes, and which becomes evident on 

 insulating the boiler. 



When steam much mixed with water, or what engine-men 

 call " wet steam," escapes from a boiler, it evidently cannot 

 be very highly electrical, for the negative water will tend to 

 neutralize the positive steam, and this may perhaps in some 

 measure account for the increased effect in the Lightning on 

 lowering the water within its boiler, and for the increase of 

 intensity in every boiler, observed when the valve has been 

 forcibly held down and is suddenly opened ; but it does not 

 seem sufficient to account entirely lor these variations of inten- 

 sity, nor for the difference of intensity in different boilers at the 

 same pressure. It is therefore probable that chemical action 

 between the metal of the boiler and the water has something 

 to do with exalting the electrical condition of the stearn at the 

 moment it is generated ; but this part of the subject certainly 

 requires further investigation. By far the most powerful ef- 



