280 



ELECTRICITY. 



into view on a signal-box placed by the side 

 of the track, a short distance in advance of the 

 lever, thus notifying the engineer that he can 

 go ahead without danger. But when the switch 

 or drawbridge is out of place, the pressure of 

 the wheel on the same lever as before brings 

 into view in the same signal-box a red flag or 

 danger-signal, and rings two bells loudly at the 

 same time one at the signal-box and the 

 other at the drawbridge. These bells keep up 

 a continuous alarm until the wheels pass an- 

 other lever, which operates a circuit-breaker, 

 located at a short distance from the switch or 

 drawbridge. The bells can be heard at the dis- 

 tance of a mile. 



A new plan of electric signals for brake- 

 men is thus described: "An electro-magnetic 

 telegraph, worked by a small battery, extends 

 from the cab of the locomotive through the 

 whole length of the train. There is an alarm- 

 bell in the cab and upon each car. Two wires 

 pass between the cars, covered with tarred 

 twine. One end of this 'cable' is securely 

 fastened to the car, while at the other end is a 

 copper link, which is placed on a spring-ham- 

 mer on the other car. This link, when in its 

 proper position, keeps the connection open. 

 It is so arranged that, should a part of the 

 train become detached, the link is pulled off, 

 the circuit is broken, and the bell on the loco- 

 motive and on each car is kept ringing until 

 the circuit is again closed. Besides automati- 

 cally indicating the breaking of a train, the 

 apparatus is useful in signalling between the en- 

 gineer and his brakemen. Instead of blowing 

 the whistle to notify them to apply or let off 

 the brakes, the engineer simply touches a little 

 knob that rings the bell on each car almost 

 instantly. By this method the brakeman on 

 the rear car is notified as surely as though on 

 the first, which is not the case by the present 

 arrangement, for it frequently happens that 

 the sound of the whistle does not reach the 

 end of a long train. If there is trouble in any 

 car, the conductor or brakeman touches a lit- 

 tle knob, the signal is given, the engineer and 

 the other brakemen are warned, and the train 

 is stopped." 



Thermo-electric Action of Metals in Liquids. 

 In an investigation of the development of 

 electric currents of unequally-heated metals in 

 liquids, Mr. George Gore found that hot plati- 

 num was electro-negative to cold platinum in 

 liquids of acid reaction, and positive to it in 

 alkaline ones, provided in all cases chemical 

 action is completely or sufficiently excluded. 

 In a later series of experiments he endeavored 

 to ascertain what electrical changes are pro- 

 duced in cases where chemical action more 

 rarely occurs ; and in those experiments he 

 employed copper plates, which are more easily 

 corroded than platinum. The following are 

 some of the general results arrived at : 



The results show that hot copper was positive to 

 cold copper in the following liquids : hydrochloric, 

 hydrocyanic, boracic, and tribasic ortho-phosphoric 



acids : chloride of copper (weak solution) ; chloride 

 of cobalt ; chloride of manganese ; chromic acid ; 

 chloride of chromium ; sulphate of zinc (weak solu- 

 tion) ; sulphate of magnesia ; chloride of calcium ; 

 nitrate and chloride of strontium ; chloride of bari- 

 um ; nitrate of sodium (strong solution) ; chloride, 

 iodide, carbonate, and biborate of sodium ; sulphate 

 of sodium (strong solution) ; tribasic phosphate oi 

 sodium ; nitrate, chloride, and chlorate of potassium ; 

 bromide of potassium (strong solution) ; iodide ol 

 potassium (strong solution) ; carbonate, acid car- 

 bonate, and bichromate of potassium ; aqueous am- 

 monia ; chloride of ammonium ; cyanide and ferro- 

 cyanide of potassium ; acetate of zinc ; and acetate 

 of sodium. And negative in the following ones : 

 nitric, chloric, hydrobromic, hydrofluosilicic, and 

 sulphuric acids ; ferrous sulphate ; chloride of copper 

 (strong solution) ; sulphate of copper ; sulphate of 

 zinc (strong solution) ; nitrate and iodide of sodium 

 (weak solutions) ; bromide and iodide of potassium 

 (weak solutions) ; iodate of potassium ; chrome alum : 

 nitrate of ammonium ; oxalic, acetic, tartaric. and 

 citric acids. The number of liquids in which hot 

 copper was positive was thirty-six, and those in 

 which it was negative was twenty. 



In several instances where the hot metal was nega- 

 tive with a weak solution, it became positive with a 

 strong one ; for instance, with sulphate of zinc, ni- 

 trate, iodide, and sulphate of sodium, bromide, and 

 iodide of potassium ; but with chloride of copper 

 the reverse occurred. These results may be con- 

 nected with the fact that in weak neutral solutions 

 the chemical action is generally the most feeble, and 

 therefore interferes the least with the direct influence 

 of the heat in producing electric currents. 



The influence of free hydrochloric, hydrocyanic, 

 boracic, ortho-phosphoric, and chromic acids, was to 

 make the hot copper positive ; while that of nitric, 

 chloric, hydrobromic, hydrofluosilicic, sulphuric, and 

 some of the organic acids, was to make it negative. 



The results also show that the quantity of the cur- 

 rent obtained with any given liquid generally in- 

 creases with the number of molecules of the sub- 

 stance contained in the solution ; in some cases, 

 however, as with sulphuric acid, carbonate of potas- 

 sium, chloride of ammonium, and acetate of zinc, 

 there was a limit to this increase ; and beyond that 

 limit the quantity of the current decreased up to the 

 point of saturation of the liquid. 



In the great majority of cases the value of the de- 

 flection increased much more rapidly than the 

 strength of the solution, particularly with solutions 

 of sulphate of magnesia, and also of hydrochloric 

 acid and of chloride of sodium, probably because 

 two causes operated, viz., increased strength of so- 

 lution and diminished resistance : in a very few 

 cases, however, the opposite result took place, as 

 with solutions of chloride and nitrate of strontium. 



Inversions of the direction of the deflection, by dif- 

 ference of strength of the liquid, occurred with solu- 

 tions of chloride of copper, sulphate of zinc, nitrate, 

 iodide, and sulphate of sodium, bromide and iodide 

 of potassium. 



In certain acid liquids, viz., nitric, chloric, hydro- 

 bromic, hydrofluosilicic, and sulphuric acids, the 

 hot copper was strongly negative (^notwithstanding 

 the chemical action upon it was distinct, and in some 

 cases even strong) ; this is similar to the electrical 

 behavior of platinum in such liquids, and may be 

 attributed either to the more direct influence of the 

 heat alone (such as occurs with platinum plates), or 

 to a different influence of the chemical action pro- 

 duced by the heat. Both these causes probably 

 operate in such cases. 



It is probable that, in all cases where the hot cop- 

 per was positive in liquids of strongly acid reaction, 

 the positive condition was due to chemical action 



With some liquids, especially with solutions of 

 hydrocyanic, boracic, acetic, tartaric, and citric acids. 



