374 Mr. H. G. Armstrong on the Electricity of a Jet of Steam. 



Upon inquiry, I found that the water used in the boilers 

 was obtained from a neighbouring colliery, where it was 

 pumped out of the mine, and that the same water was used 

 for the boiler of a small high-pressure engine adjoining the 

 colliery from which the water was procured. In order, there- 

 fore, to form an opinion whether or not the phenomenon in 

 question was dependent upon the quality of the water from 

 which the steam was generated, I proceeded to examine the 

 steam evolved from the boiler to which I had been referred, 

 and which proved to be a very small one. The valve was 

 loaded with only twenty pounds on the square inch, and I 

 learned from the engine-man that no appearance of electricity 

 had ever been noticed in the steam. Upon trial, however, I 

 succeeded in obtaining very distinct sparks of electricity from 

 the column of steam which issued from the safety-valve. The 

 sparks were certainly weaker than those obtained at the other 

 engine, but this may reasonably be ascribed to the inferior 

 pressure of the steam, and smaller size of the boiler. 



I then repaired to another high-pressure engine, which 

 belonged to the same establishment, and the boiler of which 

 was supplied with rain water instead of that drawn from the 

 mine. In this case the pressure of the steam was forty pounds 

 on the square inch. The valve was inaccessible, but a powerful 

 jet of steam was obtained from the upper gauge-cock ; I could 

 not, however, obtain any trace of electricity in the steam from 

 this boiler, not even sufficient sensibly to affect the gold-leaf 

 electrometer. The presumption, then, is exceedingly strong, 

 that the phenomenon is in some way occasioned by the pe- 

 culiar nature of the water from which the steam is produced. 

 I inclose you a specimen of the incrustation*, of a month's 

 growth, deposited by the water from the mine in the boilers 

 in which it is used. 



I shall be glad to receive any further instructions from 

 you as to the proper mode of pursuing the investigation, and 

 should be much gratified to hear your opinion as to the cause 

 of this most curious phaenomenon f. 



I am, dear sir, 



Very respectfully yours, 



H. G. Armstrong. 



M. Faraday, Esq. 



* The incrustation is grey and hard ; it contains traces of a soluble 

 muriate and sulphate, but consists almost entirely of sulphate of lime, with 

 a little oxide of iron and insoluble clayey matter, carried in probably by 

 the water. There is hardly a trace of carbonate of lime in it. — M. F. 



f The evolution of electricity by vaporization, described by Mr. Arm- 

 strong, is most likely the same as that already known to philosophers on 



