on the Electricity of Steam. 4-51 



been in an indurated state before the other was deposited. 

 The layers assume a crystalline form only when they are in 

 close contact with the iron plates. 



I have also shown in the above-mentioned treatise, that 

 during the deposition of certain salts held in solution by the 

 boiling water the ebullition became interrupted, taking place 

 only at intervals, and always with a sort of explosion or sud- 

 den development of steam, which often caused the glass flask 

 to burst. During these sudden explosions the electricity of 

 the escaping steam became so distinct, that it was readily 

 indicated by a common gold-leaf electroscope; the electri- 

 city ofthe steam, on thecontrary, escaping under ordinary cir- 

 cumstances being so feeble, that it cannot be detected without 

 the aid of a condensator. 



The development of electricity during the crystallization 

 of certain salts is very well known, and many chemical de- 

 posits occur only under a certain pressure, to which the liquid 

 containing them is subjected. Thus the carbonaceous de- 

 posits in common gas retorts are entirely obviated when the 

 gas from the coals is evolved without pressure in the retorts, 

 or even in a partial vacuum. 



The columns of vapour and smoke arising from the craters 

 of volcanos generally discharge flashes of lightning in all di- 

 rections, and it is obvious that the discharged electricity is 

 owing to the expansion or condensation of the escaping water 

 gas, if not to a chemical separation in the column of smoke 

 ascending from the crater with an immense force. 



The electricity in thunder-cJouds seems likewise to arise 

 from condensation. I had once the good fortune to be im- 

 mersed in a thunder-cloud hovering round the summit of 

 Mount Brenner in the Tyrol, having with me at the time a ba- 

 rometer, thermometer, hygroscope, and an electroscope. I saw 

 the clouds forming around me on the summit of the mountain 

 into vaporous bodies of an irregular roundish shape, which 

 seemed to retain their form by an attractive force arising from 

 the centre of each individual cloud, as they had not the 

 slightest tendency to amalgamate with each other. The hy- 

 groscope close to the cloud was not at all affected, and only 

 when immersed in the cloud, it turned first a few degrees, in- 

 dicating after a few minutes the highest degree of moisture, 

 and sinking gradually back to its first point. This fluctuation 

 continued as long as I had time to observe it. The electro- 

 scope was likewise not affected at all outside the cloud. Im- 

 mersed in the cloud the gold leaves began gradually to sepa- 

 rate, the barometer at the same time slightly rising, and after 

 each discharge of lightning both instruments returned to their 



2 G 2 



