362 



RECENT PROGRESS IN PHYSICS. 



the electricity of steam boilers need not be described, as they led to 



no decisive results. We now pass to the investigations made by 



Faraday upon this subject. 



§ 7. Faraday's researches on hydro-electricity. — Tlie substance 



of the results obtained by Faraday in these researches is given in my 



Lehrhuch der Fhysik.— (Vol. 11, 2d pt., p. 82, 3d ed.) It is only 



necessary at present to give some of the details. 



The apparatus employed by Faraday (Pogg. Ann. LX, 321) was 



not intended to produce steam in quantity, or of high pressure ; his 

 Fig. 1. object being to discover the cause of 



the phenomenon, and not to increase 

 the electric development. His boiler 

 held 10 gallons ot water, and would 

 allow the evaporation of 5 gallons. 

 To this boiler was attached a pipe 



and 



about f of an inch 



^ 4| feet long 



in diameter, at the end ot which was 

 a globe about 4 inches in diameter, 

 designated in the experiments as the 

 steam globe, (fig. 1.) To this dif- 

 erent mouth-pieces could be screwed. The boiler was well insulated. 



For a mouth-piece, a narrow boxwood tube may be screwed to the 

 steam globe. If the globe contains no water, the issuing steam, after 

 the first moment, and as soon as the apparatus becomes hot_, excites 

 no electricity. But if the globe contains so much water that it passes 

 out with the steam, an abundance of electricity appears. 



Instead of the boxwood tube, the apparatus rep- Fig- 2. 



resented in fig. 2 may be used. This consists of a 

 narrow tube, into the upper side of which water 

 may be allowed to enter from the small vessel b on 

 opening the stop-cock c. If the steam globe con- 

 tains no water, and the cock c is closed, no elec- 

 tricity is obtained when the steam escapes ; but as 

 soon as the cock is opened so that the water can 

 drop into the issue pipe and be carried off with the 

 steam, electricit}' is instantly developed. 



Hence it follows that steam alone is not sufficient 

 for the development of electricity ; there must be 

 condensed steam, consequently, drops of water, 

 to rub upon the side of the escape pipe, or, in other 

 words, the electricity is due entirely to the friction 

 of the particles of water carried out by the steam. 



If, instead of pure water, a very dilute solution 

 of any salt or acid be employed in the apparatus shown infig, 

 development of electricity ceases entirely. 



This arises, as Faraday justly remarks, from the conducting power 

 of water being so much increased by these agents that the electricity 

 developed by its rubbing upon metal, or any other substance, is im- 

 mediately discharged again. The case is just the same as if we 

 attemi)t to excite shellac by flannel which is moist instead of dry. 



As ammonia increases the conducting power of water only ina 



