466 MM. Van Breda and Logeman on the 



wire made 1800 coils, the other end of which communicated with 

 the copper pole. The tube was immersed in a water-bath, the 

 temperature of which could be raised by means of a spirit-lamp. 

 When the water was at 59° F., the needle of the galvanometer 

 deviated 4°. When the lamp was lighted, this deviation was 

 seen to increase regularly. At a temperature of 152°*6 F., the 

 deviation was "7°, and at 190°-4 F. it was 11°. The increase 

 of the conductibility of the liquid by heat was therefore proved, 

 even when traversed by an excessively feeble current. Had any 

 chemical decomposition of the water taken place during this 

 experiment ? Its direct result led to the belief that such was 

 the case, but we were also fortified in this opinion by the follow- 

 ing circumstances. When the liquid was cooled, the communi- 

 cations remaining untouched, the needle of the galvanometer no 

 longer showed any appreciable deviation. When the direction 

 of the current in the column of water was reversed, the needle 

 immediately deviated 8° and returned insensibly, but in a short 

 time to 4°, at which point it remained stationary. It was con- 

 sequently an effect of the polarization of the electrodes that we 

 observed in this case, a polarization which opposed the current 

 at the first moment of its passing, without, however, being able 

 to annul it, but which annulled it completely when it had become 

 stronger by the passage of the stronger current through the 

 heated liquid. 



But is this polarization the peculiar effect, and consequently 

 the irrefragable proof, of chemical action ? There are many 

 experiments which render this opinion, if not absolutely certain, 

 at least exceedingly probable. We may mention in particular 

 those of Schonbein, who found that the effect continues when 

 the electrodes which have served to introduce a current into a 

 liquid are immersed in another liquid through which no current 

 has been passed, and also that effects exactly similar to those of 

 the plates polarized by the current may be obtained by putting 

 one of them only in contact with a gas (such as hydrogen or 

 chlorine) for a very short time, and afterwards immersing them in 

 acidulated water*. Some physicists, however, still maintain 

 the opposite opinion. They explain polarization by an accumu- 

 lation of electricity of different natures, either in the electrodes 

 themselves, or in the adjacent portions of the liquid ; these two 

 electricities in recombining by a conductor uniting the two 

 electrodes, after the connexion between these and the electro- 

 motor has been broken, would give rise to the current in the 

 opposite direction to that of the latter, which is always observed 

 in such cases. 



It appeared to us that your beautiful experiment on electro- 

 * PoggendorflPs Annalen, vol. jdvi. p. 109, and vol. xlvii. p. 101. 



