ELECTRICITY. 



Table of 



conductors. 



vergency will lill continue. The electricity, therefore, 

 poMened by the ballt,( not enable ofbcinfrcnmod off by 

 passing through these bodies. Gl.is.j, scaling-wnx, and 

 sulphur, are thence called non-condu' l^r\ <>f eK-ctrici- 

 ty, as they ihi not possess the po- nsniitting the 



electric matter. It', on the contrary, wo touch any of 

 the pith balls with a piece of any metal, with the fin, 

 at with any body cootdning moisture, the pith K-ilN will 

 instantly lose their electricity, :iiul collapse. The dec- 

 tritity.consequently, which ooc.-iMoiird their divergence . 

 has escaped, or been carried off by those bodii 

 hence they have received the name of conductors. Be- 

 tween these two classes of substances, there are others 

 which do transmit the electric fluid, but with less fa- 

 cility than those which arc called conductors, and 

 therefore they have been distinguished by the name of 

 imperfect conductor*. Substances called non-conduclort, 

 have also received the name of electrics, and sometimes 

 insulators, from their having the property of insulating 

 bodies, or forming a barrier, which prevents the com- 

 munication of the electricity of the insulated body to 

 those which surround it. The following Table contains 

 all the substances which have the property of conduct- 

 ing electricity, arranged in the order of their conduct- 

 ing power. We have followed the order assigned to 

 them by Mr Singer. 



List of Conductors. 



All the metals. 



Charcoal well burnt. 



Plumbago. 



Concentrated acids. 



Charcoal in powder. 



Diluted acids. 



Saline fluids. 



Metallic ores. 



Animal fluids. 



Sea water. 



Spring water. 



River water. 



Ice above 13" of Fahrenheit 



Snow. 



Living vegetables. 



Living animals. 



Flame. 



Smoke. 



Steam. 



Most saline substance?. 



Rarefied air. 



Vapour of alcohol. 



Vapour of ether. 



Most earths. 



Most stones. 



To thete, we may add powdered glass and powdered 

 sulphur, which have been found to be conductors by 

 the experiments of Van Swinden. 



Several of the bodies in the preceding table lose their 

 power of conducting electricity when they are made 

 very dry, and therefore they owe their conducting 

 power solely to the moisture, or the fluids which they 

 contain : hence vegetables and living animals, for exam- 

 ple, conduct electricity solely in virtue of the juices and 

 fluids which they contain. 1 he conducting power varies 

 also with the temperature. Hot charcoal and hot water 



" 



Some bodiri 

 conduit on. 

 ly notiuvc, 

 and uthera 

 only nega- 

 tive elec- 

 tricity. 



Experi- 

 ment of 

 Mr Braalfl 



trann.M .' .-c. ricity with more facility than when they 

 are co! 1 : and jjlafs, which Is a perfect Mn-fiondootor 

 when foM and dry, becomes a tolerably good conductor 

 when !u .t ed to redness; and the same change t::l\cs 

 place iipon resinous bodies when melted, and up 



.HM| when heated. Air, however, does not con- 

 duct electricity, whatever be it temperature. 



Although flame is here enumerated in the list of con- 

 ductors, yet it has been shewn by M. Erman, that the 

 ii!Mil.;tci! Harms of n>ax, oil, alcohol, and hydrogen gas, 

 o.ily conduct positive electricity ; while other substan- 

 ces, such as phosphorus-, conduct only negative electri- 

 city. Mr v'uthhcrtson had observed, '( Practical Electri- 

 city, p. 13,) that when the flame of a common candle 

 wni placed midway between two equal balls, one posi- 

 tively and the other negatively electrified, the flame was 

 attracted to the negative ball, which became very hot, 

 while the positive ball remained cold 



Mr Brandc * has endeavoured to explain these phe- 

 nomena in another manner. As some chemical bodies 

 are naturally negative, and others positive, he supposes 

 that the positive will be attracted by the negative ball, 

 and the negative by the positive ball ; and in order to 

 ascertain the probability of this conjecture, he placed 

 the flames of various bodies between two insulated brass 

 balls, one of which was electrified positively, and the 

 other negatively. By this apparatus he obtained the 

 following very interesting results : 



Substances attracted to the Positive Ball. 



Sulphurous acid vapour. 



A small flame of phosphurettcd hydrogen slightly .t 



Fumes of white arsenic slightly. 



Large flame of carbonic oxide. 



Vapour of burnt sulphur. J 



Flame of phosphorus. 



Vapour of phosphorus. 



Stream of muriatic acid. 



Stream of nitrous gas. 



Vapour of benzoic acid. 



Substances attracted to the Negative Ball. 



Olefiant gas. 



Sulphuretted hydrogen slightly. 



Arsenicated hydrogen. 



Flame of hydrogen weakly. 



Sulphuret of carbon. 



Potassium in combustion, and its fumes. 



Flame of benzoin. 



Smoke of benzoin. 



Charcoal emitted by camphor in combustion. 



Resinous bodies exhibit the same phenomena as 



camphor. 

 Amber exhibits the same phenomena as benzoin. 



Dr Priestley found the conducting power of charcoal Charwti 

 to vary very much in different pieces of that substance; 

 and it has since been found, that this variation arises 

 from, and is proportional to, the different degrees of 

 heat that have been employed in making it. 



The conducting property of ice was first discovered '** 

 by M. Jallabert, and confirmed by Dr Priestley. M. 

 Achard of Berlin, however, observed, in January 1776, 

 that ice, at the temperature of 13" of Fahrenheit, lost 





See PkUompkical Traniactiont, 1814, Part I. 



t A Urge flame of this sutwtaoce was equally attracted by both balls. 



$ The direction of the flame could not be determined. 





