10 Mr. G. Gore on the Development of Dynamic Electricity 



lowing cases : — Ist^ that under the influence of heat, acid liquids 

 act upon metals differently to alkaline ones ; either the hot plate 

 dissohiug most in the case of acids, and the cold one in the case 

 of alkalies, or vice versa, the plate most freely acted upon being 

 positive in all cases ; or 2nd, that the hot plate dissolves most in 

 both cases, but with acids the dissolving metal acts as a base and 

 is positive, whilst with alkalies it acts as an acid and is negative. 



31. If either hypothesis be true, experiment ought to ac- 

 cord. To test them, I mixed together a quarter of an ounce of 

 sulphuric acid and 8 ounces of a solution composed of 220 

 grains of sulphate of copper dissolved in 10 ounces of water, and 

 then accurately balanced two equal quantities (about 3 ounces 

 each) of the mixture. I put the two portions in separate large 

 glass flasks with two pieces (one in each) of copper foil, each 

 2x2 inches, of the same thickness, perfectly clean, and cut from 

 contiguous parts of the same piece of metal ; kept each exactly 

 ten hours in its liquid, one being at about 65° F., and the other 

 maintained at a temperature of about 200° F. the whole of the 

 time, the small amount of water which evaporated from the hot 

 one being occasionally replaced. The hot liquid in a few hours 

 became manifestly deeper in colour, and the piece of metal in it 

 gradually blackened, whilst the other solution and its metal did 

 not visibly alter. The pieces of metal were taken out at the end 

 of the ten hours, rinsed in water, dried and weighed ; the one 

 from the cold liquid, which previously weighed 23'7 grs., had 

 lost only O'l gr., whilst the other, which weighed 24"0 grs., had 

 lost 6*4 grs., and was quite dark in colour, the cold one being 

 but moderately tarnished. When the hot portion of the liquid 

 had cooled, I mixed it with the other portion, filtered, and intro- 

 duced it into the apparatus (7) with copper plates, and tried it 

 in the usual manner. The cold plate was positive, the deflection 

 of the galvanometer needles being 54 with the top plate at 

 208° F., and the lower one at 65° F. I repeated this experi- 

 ment with the same liquid and very thin copper plates ; the cold 

 plate was again positive, the deflection being 51 with the upper 

 plate at 206° F. In both of these experiments the upper plate 

 alone was blackened on taking the apparatus to pieces. 



32. In these cases there was doubtless more chemical action at 

 the upper plate than at the lower one ; yet notwithstanding this 

 the lower plate was positive, which I attribute to the action of 

 some other cause than chemical action. These instances are ex- 

 ceedingly clear ones, and the results are invariably the same with 

 all solutions of sulphate of copper, acidulated or pot, or of various 

 degrees of dilution, when examined either with copper, silver, or 

 platinum plates. 



33. The following experiments also show that the currents 



