ELECTRU'ITY, ANIXAL. 



ELECTRO-CHEMISTRY. 



803 



mi ; dress M the growing warmth of the air enable* It to hol.l u 

 till larger amount of vapour uncondensed, and u the vapour iUelf 

 rice* rapidly to form cloud ; increaaei again iuwanU the evening, when 

 dew begin* to form at sunset and vapour to settle into globules, and 

 one* more decreaaes u the number of these electrified globules dinii- 

 ulshes by deposition and diffusion. A Urge portion of the electricity 

 near the surface U returned to the earth by alow conduction, un.l the 

 more ao in proportion a* the air u moist. The great and mddsfl 

 increase of electrical tendon, sufficient to produce a flash of lightning, 

 and a torrent of rain, will be noticed under LKIHTNIXO ; RAIN. 



The aurora borvalia, and some other meteoric appearances, have been 

 ascribed to the electricity of the atmosphere. [I'OLAB LIGHTS.] 



KLKCTltlcn V ANIMAL. [ELECTRICITY OF OBOANIC BEINGS, 

 NAT. Hivr. Div.J 



KI.KiTHirlTY, Meiliral application of. A supposed analogy between 

 i-livtricity ami Uie nervous power has led to the employment of this 

 agent, particularly in diseases connected with defective nervous energy, 

 and also in cases of defective secretion, perhaps originating in a similar 

 oause. The influence of electricity on the human system differs much 

 according to the manner in which it is applied, the length of time 

 during which it is continued, and the degree of intensity. It also 

 differs in its action according as it U abstracted from, or communicated 

 to, the individual. When applied in a moderate degree of intensity, it 

 occasions an increase of nervous action, of sensibility and irritability, 

 more vigorous circulation of the blood, augmented warmth, and secre- 

 tion, especially cutaneous transpiration : even the exhalation of plants 

 is much increased by electricity. When the electric principle is more 

 intense, all these actions ore heightened, often to a painful degree ; 

 while such a degree of concentration as occurs during certain atmos- 

 pheric changes can occasion instant death. Death occasioned by this 

 means is always followed by rapid decomposition of the body. The 

 diseased states in which electricity has been found most useful are in 

 asphyxia, from any cause (except organic disease of the heart), but 

 particularly from exposure to irrcapirable gases ; in certain asthmatic 

 diseases ; and dyspepsia, dependent on irregular or defective supply of 

 nervous energy to the lungs and stomach. It is, however, much 

 inferior to galvanism as a remedial agent in these diseases. (Wilson 

 I'hilip ' On the Vital Functions.') In local paralytic affections, when 

 of a chronic character, electricity, duly persevered with, has been found 

 very useful : in a case of dygphagia, from paralysis of the oesophagus, 

 the patient could only swallow when placed on a seat resting on non- 

 conductors and electrified. In deafness and loss of sight, when directed 

 by a competent judge, it has restored the functions of seeing and 

 hearing. Lastly, in defective secretion, especially amenorrhcca, it has 

 proved of service. Recently, M. Becquerel and others have employed 

 electricity, with complete success in six cases, where the milk has been 

 suppressed, as an exciter of the mammary secretion. 



ELECTRO-CHEMISTRY. Electricity, like heat and light, both 

 affects and U affected by chemical change : and just as heat more often 

 appears as a cause or consequence of chemical change than does light, 

 so galvanic, or low-tension (voltaic) electricity is more prominently 

 concerned as cause or effect in chemical change, than is the so-called 

 frictioual or high-tension electricity. Hence, in electro-chemistry, the 

 relation of chemical change to galvanic electricity has almost exclusively 

 to be considered. 



The order will be adopted of considering (1) the chemical changes 

 effected by a galvanic current; (2) the galvanic current produced by 

 chemical Mumgaa, 



If the two poles of a battery be brought into contact with two points 

 of a homogeneous substance, the substance may either conduct the 

 current without suffering chemical change, it may refuse to conduct 

 tlie current at all, or finally it may conduct the current and suffer 

 chemical change. 



No instance is known in which a true chemical compound con- 

 ducts a current without suffering chemical alteration ; but substances 

 which are simple, as far as evidence goes, may refuse to conduct a 

 current. Moreover no chemical compound substance conducts unless 

 in a state of liquefaction, such liquefaction being caused either by solu- 

 tion in media or by igneous fusion. 



As a class, the metals are the best conductors of electricity. With 

 regard to the resistance offered to a galvanic current by various con- 

 ductors, some of which are unaltered, some decomposed by it, we may 

 compare the numbers of the following table (Buff, Zamminer, and Kopp's 

 ' lychrbuch '), in which the resistance to the same galvanic current 

 offered by the same lengths and thicknesses of some conducting sub- 

 stances u given, the resistance offered by silver being taken as unity : 

 SUrer ........ 1-000 



Cupper (chemically pure) ... 

 Copper (commercial) .... 



Bnut (composition not stated) . . 



Platinum >.... 



German lilrer (competition cot luted) . 



Mercury 



Sulphuric acid ((>. gr. 1-2 to 1-30) . . 



Sulphate of line (3V53 pr, r,nt. of anbydroui 1 I10100I ,. oor 



ult in solution ....... ) ' ' 



Sulphate of copper (20-K3 fa- rent, of anbjrdrotu ( . 



salt in tolution) ...... j H80SJO'( 



1-043 

 1-270 

 9-372 

 8-427 

 9*590 

 1 2-400 

 29-238 

 761732-000 



i what has been said, it follows that the Utter three of these 

 substances are decomposed during the passage of the current tl. 

 them. The presence of more than one element in brass and German 

 silver is not in contradiction to the general rule laid down ; for the 

 metals present in these alloys are not in chemical union, and the alloy 

 conducts the current in the same manner as would a bundle of 

 consisting in part of one metal, in part of the other. The conducting 

 power of the metallic conductors is diminished by an increase of tem- 

 perature, that of the compound solutions is always increased. 



In examining the nature of the changes wrought in compound con- 

 ductors when submitted to, and therefore decomposed by, the electric 

 current, it will be convenient to suppose, in the first place, tl. 

 poles by which the current is led through the substance are themselves 

 chemically inactive, that is, of such a nature as not to be acted on \<y 

 any of the products of decomposition. In practice, when this passivity 

 is desired, the poles are usually made of platinum, and this will in the 

 sequel be always tacitly assumed to be the case, unless the contrary be 

 KXMM 1 1. 



The decomposition of a compound substance by galvanic electricity 

 is called the electrolytic of that substance. The body so decomposed is 

 called an electrolyte. The two poles between which the current passes 

 through the electrolyte are the electrode!. The positive ( + ) electrode, 

 or anode, is the one in metallic connexion with the inactive element of 

 the battery (Platinum, Carbon). The negative () electrode, or caf/i./. . 

 U in connexion with the active or attacked element of the acting battery 

 (Zinc). The products of electrolysis of the electrolyte are sometimes 

 called ton*. That ton which appears at the negative electrode or cathode 

 is the cation ; that at the positive electrode or anode is called the union . 

 (According to strict analogy, this latter nomenclature should be in- 

 verted.) 



Thus, if the two platinum poles of a battery be inserted into a 

 solution of chloride of hydrogen (hydrochloric acid), chlorine is liberated 

 at the positive electrode or pole, and hydrogen at the negative one : in 

 the manner of the skeleton diagram : 



H 



Cl 



Ztt Pt 



If water be substituted for hydrochloric acid, oxygen appears at the 

 positive pole, hydrogen at the negative one. If solutions of other 

 chlorides be used, such as chloride of copper, of gold, &c., the metal ifl 

 precipitated at the same pole (the negative) at which the hydrogen was 

 evolved, the chlorine at the positive one. In accordance with that 

 terminology built upon the indistinct notion that unlike things seek to 

 approach, and that, conversely, things which seek one another do so by 

 virtue of dissimilarity or oppositeness of their conditions, those ions 

 which appear at the negative pole are called electro-positive, those which 

 are set free at the positive pole are called electro-negative. Thus, in the 

 instances given : 



H 

 H 



Cu 

 Au 



O 



Cl 

 Cl 



Cl 



Water. 



Chloride of hydrogen. 

 Chloride of copper. 

 Chloride of gold. 



the elements in the first column are electro-positive, those in the second 

 electro-negative. 



If now, instead of binary compounds of this kind we submit aqueous 

 solutions of oxygen acids, or salts of such, to electrolysis, we find that 

 in the first instance, that is, in the case of the free acids (or hytl 

 salts) hydrogen is liberated at the negative pole and oxygen at the positive 

 one. If a metallic salt of such an acid be electrolysed, the metal is 

 deposited at the pole where hydrogen is liberated, while oxygen, as 

 before, escapes at the positive pole. It is by laying weight upon the 

 analogy of decomposition, in the cases of binary salts and oxygen ones, 

 that the similarity of then- constitution has been supported. For, it" 

 we imagine the electric current to enter the electrolyte by the positive 

 pole (anode), and to withdraw all the negative atoms (chlorine) of the 

 molecules of hydrochloric acid in contact with it; as the hydrogen 

 so freed does not escape in loco, it is easy to imagine the atoms of 

 hydrogen to decompose the molecules of hydrochloric acid in their 

 neighbourhood, liberating hydrogen again, and that these decompose 

 fresh molecules of hydrochloric acid, liberating hydrogen, and so on. 

 So that, wherever the cathode may be, that is, wherever the negative 

 pole is situated and such successive decomposition has to cease, in con- 

 sequence of the current finding a metallic conductor (the cathode) by 

 which it may leave the electrolyte, it is clear that there hydrogen will 

 be evolved. As the results of the electrolysis of sulphuric acid and the 



