ELECTRICITY. 



831 



mid restoring them to the metallic state. When a 

 succession of electric discharges from a powerful 

 electric machine are sent through water, a decom- 

 position of that fluid takes place, and it is resolved 

 into its two elements of oxygen and hydrogen, which 

 immediately assume the gaseous form. When this 

 experiment is conducted in a suitable apparatus, and 

 ii shock is transmitted through the mixed gases thus 

 obtained, they are instantly kindled ; a rt-union of 

 the elements takes place ; and precisely the same 

 quantity of water is reproduced as was decomposed 

 to furnish the gases. It may appear somewhat para- 

 doxical that the same agent should, in the course of 

 the same experiment, produce at one time decom- 

 position, and at another combination, of the same 

 elements. The simplest way of reconciling this 

 apparent discordance, is to suppose that the combi- 

 nation of the gases is the effect of the heat evolved 

 during its forcible transit through an aeriform fluid 

 that opposes considerable resistance to its passage j 

 while the decomposition of the liquid is the direct 

 consequence of the agency of electricity when 

 not interfered with by heat. When a solution of 

 sulphate of copper is subjected to the action of elec- 

 tricity by means of slender conducting wires termin- 

 ating in the vessel containing the solution, the copper 

 is revived, or precipitated in a metallic state, around 

 the negative wire ; but upon reversing the direction 

 of the current of electricity, so that the same wire 

 now becomes positively electrified, the copper which 

 has collected around it is redissolved, and a similar 

 deposit takes place on the opposite wire, which now 

 becomes the negative one. Similar experiments, 

 made with other metallic solutions, are attended with 

 similar results ; and solutions of neutral salts with 

 alkaline and earthy bases obey the same law, 

 being separated into their constituent parts, the 

 ingredient containing oxygen always appearing 

 at the positive wire, and the base at the nega- 

 'tive wire ; but as these are a class of effects which 

 have been more particularly investigated by that 

 mode of agency denominated galvanism, we shall 

 reserve a more full account of them for that 

 article. 



IX. Having seen the effects of electricity on inani- 

 mate matter, we now proceed to describe the agency 

 it exerts over living bodies. Its passage through 

 living plants immediately destroys the vitality of the 

 parts through which it passes. A very small shock, 

 sent through the stem of a balsam, causes its leaves 

 to droop in a few minutes, and finally extinguishes 

 its vitality. The approach of an electrified conduc- 

 tor to the sensitive plant (mimosa pudica) produces 

 no effect upon it ; but when sparks are taken from it, 

 the leaves collapse, just as they are accustomed to do 

 from concussions of a mechanical nature. When the 

 energetic effects of the shock from the Leyden vial 

 upon the animal system were first made known, high 

 expectations were raised that electricity would 

 prove a remedial agent of extraordinary power. It 

 was supposed that, as a stimulant, it would have 

 many advantages over other remedies ; for it can be 

 administered in various degrees of intensity, which 

 may be regulated with great exactness ; and its appli- 

 cation can be directed especially to the organ we 

 wish to affect. Accordingly, we find, at one period, 

 it was employed in a great number of cases : but at 

 present it Ls confined to a very few ; such as palsy, 

 contractions of the limbs, rheumatism, St Vitus's 

 dance, some kinds of deafness, and impaired vision. 

 Although the effects of ordinary shocks upon living 

 animals are familiar to most persons, still a short 

 account of these shocks, as they have been adminis- 

 tered out of the common course may not be uninter- 

 esting. If a person who is standing receive a charge 



through the spine, he loses his power over the 

 muscles to such a degree, that he either drops on hist 

 knees, or falls prostrate on the ground. A strong 

 charge passed through the head gives the sensation 

 of a violent but universal blow, and is followed by a 

 transient loss of memory and indistinctness of vision. 

 If the diaphragm be included in the circuit of a 

 coated surface of two feet in extent, fully charged, 

 the sudden contraction of the muscles of respiration 

 will act so violently upon the air in the lungs, as to 

 occasion a loud and involuntary shout ; but if the 

 charge be small, a fit of convulsive laughter is 

 induced, producing a most ludicrous scene to the by- 

 stander. Small animals, such as mice and sparrows, 

 are instantly killed by a shock from thirty square 

 inches of glass. 



X. There are several mineral bodies, which, from 

 being in a neutral state at ordinary temperatures, 

 acquire electricity simply by being heated or cooled. 

 This property is confined to crystallized minerals ; 

 and of these the most remarkable are the tourmaline 

 and boracite (q. v.). In the former of these, it is 

 best observed in the regularly terminated crystals. 

 When one of these is heated from 100 to 212 Fahr., 

 the extremity terminated by the greatest number of 

 planes becomes charged with positive electricity, 

 while the other extremity is negative. When the 

 crystal is of considerable size, flashes of light may be 

 seen along its surface. A large number of substances 

 become electrified on passing from the liquid to the 

 solid form. This happens to sulphur, gum-lac, bees- 

 wax, and, in general, all resinous bodies. The con- 

 version of bodies into the state of vapour, as well as 

 the condensation of vapour, is generally attended 

 by some alteration of their electrical condition. Thus, 

 if an ignited platina crucible be placed upon the gold 

 leaf electrometer, and water be dropped into it, at 

 the moment the vapour rises, the leaves of the elec- 

 trometer diverge with negative electricity. Elec 

 tricity is evolved by the contact of different metals. 

 Thus, if two discs, the one of copper, the other of 

 zinc, rather more than two inches in diameter, and 

 furnished with insulating handles, be brought into 

 contact, and then separated and examined by an 

 electroscope, the copper disc is found to be charged 

 with negative, and the zinc with positive electricity. 

 While the contact of the metals is preserved, neither 

 of them gives any indication of its electrical state, 

 the electricity being disguised until the separation 

 takes place. This observation has an important re- 

 lation to the theory of that mode of electrical excite- 

 ment called galvanism, under which head it will be 

 resumed. There are some bodies which are rendered 

 electrical by pressure. Thus, if a crystal of calca- 

 rious spar or arragonite be pressed for a few mo- 

 ments between the fingers, it exhibits a decided 

 attraction. The same thing happens with regard 

 to cork, paper and wood. Many mineral substances, 

 when reduced to powder, exhibit electricity, if made 

 to fall upon an insulated metallic plate, a mode of 

 excitation which is to be considered as a species of 

 friction. The most important circumstance in this 

 inquiry is the connexion between electricity and the 

 chemical properties of matter, first pointed out by 

 Sir H. Davy. Most of the substances that act dis- 

 tinctly upon each other electrically, are likewise such 

 as act chemically, when their particles have freedom 

 of motion. This is the case with the different me- 

 tals, with sulphur and the metals, with acids and the 

 alkaline substances. Of two metals in contact, the 

 one which has the greatest chemical attraction for 

 oxygen acquires positive electricity, and the other 

 the negative. In the contact of acids with bases, as 

 of crystals of oxalic acid with dry quicklime, the 

 former is negative, the latter is positive. All acid 



