[ 49-i ] 

 LXIX. Intelligence and Miscellaneous Articles. 



NOTE ON THE ELECTRICITY DEVELOPED DURING EVAPORATION 

 AND DURING EFFERVESCENCE FROM CHEMICAL ACTION. BY 

 PROFESSOR TAIT AND J. A. WANKLYN, ESQ. 



ONE of Professor W. Thomson's divided-ring electrometers having 

 been recently procured for the Natural Philosophy collection in 

 the University, we have made use of it in repeating and extending the 

 experiments of Volta, Pouillet, and others, on the electricity pro- 

 duced during the evaporation of various bodies. In some cases our 

 results agree with those already known, but in others w r e find effects 

 differing totally in kind or degree from the accepted ones ; and with 

 some substances we find occasionally contradictory indications among 

 our own results. 



The electrometer is in every respect a far superior instrument to 

 the gold-leaf electroscope, which (sometimes w r ith the addition of a 

 condenser) was used by former experimenters, and enables us to give 

 our results in a form easily reducible to absolute measure. The 

 charge of the instrument was such that, when the half- rings were 

 respectively connected with the zinc and platinum of a single Grove's 

 cell, the deflection observed amounted to about 5*8 scale divisions. 

 This was found to be the most useful charge for the bulk of our expe- 

 riments, but it was easily increased twenty or thirtyfold when we 

 sought to verify any very delicate indications. 



Our apparatus consisted of a platinum dish, placed on an insula- 

 ting stand, and connected with the insulated half-ring. A lamp 

 could be placed on the stand so as to heat the dish ; and w r hile this 

 was going on, the indications of the electrometer gave us the atmo- 

 spheric charge. The experiments were all conducted when the latter 

 was very small ; so that, although the sputtering of the fluids dropped 

 on the hot plate may have prevented us from observing some slight 

 effects, the large deflections we observed in many instances can have 

 nothing to do with the electric state of the air of the room. With a 

 different disposition, w T hich enabled us to use a Bunsen lamp to heat 

 the dish, we obtained the atmospheric potential by burning a little 

 ether or alcohol on the dish itself when the lamp was removed. 



We agree generally with previous experimenters, that during the 

 continuance of the spheroidal state there is little, if any, perceptible 

 disengagement of electricity. We also agree with the statement that 

 the main effect is produced while the fizzing sound that accompanies 

 the loss of the spheroidal state is heard, and that during the conti- 

 nuance of the mechanical action to w T hich that sound is due the 

 indications of the electrometer in general steadily increase. That 

 the greater part of the electricity produced is due to friction is proved 

 by the fact that when fluids are forcibly squirted upon the hot dish 

 the electrical indications are very much increased, and that a con- 

 cave surface gives far more powerful deflections than a convex one 

 at the same temperature. The sputtering or violent boiling which 

 succeeds the fizzing state shows little, if any, disengagement of 

 electricity. The principal interest of the results which we have 

 obtained is in the cases of iodine, bromine, and various other 



