198 M. W. Beetz on the power of conducting Electricity 



lead might have been admixed, and thus have been electrolysed ; 

 by no reagent, however, could any such compound be detected ; 

 and on allowing the current to pass through the fluoride of lead 

 for six hours, the deflection of the galvanometer needle remained 

 constant during the whole period. The experiment was repeated 

 with a specimen of fluoride of lead which M. H. Rose had 

 kindly given me, and in which I also failed to detect any foreign 

 substance ; exactly the same results were obtained, so that fluo- 

 ride of lead may decidedly be considered as an electrolyte. 



Experiments on substances containing silicic acid, showing 

 how their power of conducting commences when heated, have 

 .long since been made known. After Cavendish* had demon- 

 strated this conducting power for frictional electricity in glass, 

 and Delavalt in Portland and several other stones, AldiniJ was 

 able to produce contractions in a prepared frog by connecting 

 the two metals which were placed on muscle and nerve by means 

 of a piece of glass fused before the blowpipe. And although 

 Ritter§ claimed an insulating power for red-hot glass, yet PfafF|| 

 received continuous shocks when with both hands he completed 

 the circuit of a voltaic battery into which a glass tube heated to 

 redness and almost to fusion was inserted. Later, when he cor- 

 roborated these statements, Ritter^ proposed the following 

 questions : — " Of what nature is the conducting power of those 

 individuals of this class of bodies that ultimately conduct ? Do 

 they conduct in the same manner as water, or in the same 

 manner as metals, i. e. with or without decomposition, or more 

 definitely in Volta^s language, as conductors of the first or of the 

 second class ?" In the foregoing case this last question was 

 exactly the one under discussion. For my first experiments I 

 selected Fuch^s water-glass, which, on account of its simple com- 

 position, may be considered as a type of all the other silicic-acid 

 compounds. This glass was prepared without any addition of car- 

 bon, and was almost colourless or white. A sfhall narrow bar of it 

 was placed on two strips of platinum and strongly heated until it 

 fused fast to them, it was then allowed to cool again. When 

 cold, it <;onducted the current of a battery connected with the 

 two pieces of platinum ; when gently heated or dried over sul- 

 phuric acid, it was a perfect insulator. When strongly heated, 

 but not to fusion, it became a good conductor, and from the first 

 motion of the astatic system in the galvanometer which was in- 

 troduced into the circuit, it was evident that the platinum plates 



* Franklin's Experiments and Observations. London, 1774, p. 411. 



t Priestley, Gesch. d. Elecfr. Deutsch v. KrUnitz, 1772, p. 150. 



X Aldini, Versuche, ubers. v. Martens, 1804, vol. ii. p. 76. 



§ Gilbert's Annalen, vol. vi. p. 471- 



II Ibid. vol. vii. p. 249. f Ibid. vol. ix. p. 290. 



