265 



GALVANISM. 



GALVANISM. 



200 



at the negative, in the same proportions in which they constitute that 

 liquid ; but if oxidable, then the positive wire will be covered with an 

 oxide, while the negative wire still produces hydrogen gas. In general | 

 oxygen and chlorine are found at the positive pole, and the other gases 

 at the negative ; but we are not to suppose that oxygen only is 

 disengaged by one wire, and hydrogen only by the other ; for the 

 particles of water in contact with the ends of either wire are strictly 

 decomposed into their constituent gases, but the oxygen formed at the 

 negative wire is transferred to the positive, and the hydrogen at the 

 positive is transferred to the negative. 



The chemical analysts were at first somewhat puzzled at finding 

 foreign products, when producing decomposition by galvanism ; soda, 

 which was sometimes found, was due to the decomposition of small 

 portions of the glass in which the experiments were made, and 

 muriatic gas to vegetable substances employed occasionally, as wet 

 cotton-thread, when the liquid was contained in separate vessels having 

 only this mutual communication. 



When neutral salts were held in solution and exposed in the same 

 manner to the galvanic action, their alkaline bases were found at the 

 negative wire, and the acid at the positive : thus zeolite was decomposed 

 into soda and lime ; glauber salt into solution of soda and sulphuric 

 acid ; while the metallic solutions gave their crystals and oxides to the 

 positive pole, and transferred the acids to the negative. Davy made 

 the remarkable discovery that this transfer took place without any 

 combination being effected with the parts of the medium traversed, 

 even when the latter had a great affinity for the elements which passed 

 through it. He arranged three cups, in the first of which was a 

 solution of litmus, in the second a similar solution, and in the third 

 sulphate of soda. The positive wire was immersed in the first cup, the 

 negative in the third ; and the intermediate one was connected with 

 the two extreme cups by means of a moistened thread, so as to com- 

 plete the circuit : the result was, that the solution of litmus in the 

 positive cup became red, indicating the transfer of the acid from the 

 third cup, while the similar solution in the intermediate cup underwent 

 no change, clearly showing that the acid in its transfer did not combine 

 with the solution through which it passed. Similarly, upon reversing 

 the poles, a green was produced in the first cup, while the middle still 

 remained unaffected. But he soon recognised that there was an 

 exception to this, namely, when the transmitted substance and the 

 medium combine so as to form an insoluble compound ; for when it 

 has thus acquired a greater specific gravity than the medium, it is 

 necessarily drawn out of the line of transference ; and if by mechanical 

 means it should be preserved in it, the transfer will go on as before. 



It may be observed generally, with respect to chemical decompo- 

 sitions effected by galvanism, that it is quantity rather than intensity 

 which is requisite, and that the metals, alkalies, and earthy bases are 

 transferred to the negative pole ; the acids, oxides, and chlorides to the 

 positive. By the successive labours of Davy and other chemists, 

 different substances which had before been supposed simple, as soda, 

 potash, lime, baryta, strontia, magnesia, zircon, &c., were analysed 

 by this powerful instrument ; and though silex, alumina, tc., offered 

 great resistance to its application, and the metallic bases were with 

 difficulty restrained from again combining with oxygen, still in the 

 majority of cases the analysis has been successful. The same method 

 was applied by Brande to fluids containing albumen, when albumen 

 and alkali were found at the negative pole, albumen and acid at the 

 positive ; he also found that though it remained fluid with a weak 

 battery, when a stronger one was employed it was separated in a 

 coagulated form. Experiments of the same nature were made by 

 Golding Bird, whose results do not agree with those obtained by 

 Brande. He used for his battery the Voltaic form, a Couronne de 

 TOMU of thirty small plates, excited only by a weak solution of salt, 

 and first operated on liquid albumen in a state of non-combination. 

 Tutting serum of blood into a glass vessel, and having introduced the 

 wires of the battery, a cloudy deposition took place near the positive 

 wire without adhering to it. The experiment being next made with 

 two vessels connected by moistened cotton, coagulation took place in 

 the positive vessel, while none occurred in the negative ; after a time 

 the contents of the former had an acid taste, and of the latter a caustic 

 alkaline flavour : when all in the positive vessel was coagulated by the 

 galvanic action, he found there hydrochloric acid mixed with chlorine, 

 and the alkali in the negative vessel. He has given also an explanation 

 of the causes of the difference in Brande's results. 



An interesting class of experiments is due to Mr. Crosse on the 

 employment of electricity, in a state of high tension, to form mineral 

 and other substances. There is a cavern near Broomfield, of which the 

 vault is covered with arragonite and carbonate of lime and fine crystals. 

 The water which drips from this vault holds in solution ten grains of 

 carbonate of lime and a little sulphate of the same to each pint. A glass 

 IHed with this water was submitted to the action of a battery con- 

 sisting of 200 pairs of plates, and at the expiration of ten days the 

 negative pole was found to have formed rhomboidal crystals of car- 

 bonate of lime, accompanied by some gas-bubbles, and in less than a 

 month after the wire was covered with regular and irregular crystals, 

 whence it follows that the bi-carbonate was decomposed into carbonate 

 and carbonic acid gas. He also let the water drop on a piece of brick 

 ubjected to a current from 100 five-inch plates, the brick being gup. 

 ported V'y a funnel which conducted the water into a vessel below ; 



after four or five months the brick near the negative pole of the battery 

 was covered with carbonate of lime, while near the positive pole were 

 disposed prismatic crystals of arragonite; and the same experiment 

 being repeated with fluosilicic acid, regular hexahedral pyramids similar 

 in all respects to quartz were obtained ; those which were left in a dry 

 place acquired sufficient hardness to scratch glass ; the others had not 

 that power, and gradually lost their transparency. In his varied ex- 

 periments of this nature he succeeded in forming, by means of the 

 galvanic battery, the following minerals : carbonate of lime ; arra- 

 gonite ; quartz ; protoxide of copper ; arseniate of copper, and its blue 

 and green carbonates ; phosphate of copper ; carbonate of lead ; chalce- 

 dony, &c., xipon which Becquerel remarks, in hia ' Experimental Elec- 

 tricity,' " nearly all these substances we have obtained these dozen 

 years with the simple electro-chemical apparatus." 



We now pass on to a brief notice of the physiological effects pro- 

 duced by galvanism, from which we must exclude any account of the 

 animalculse observed by Mr. Crosse in the solutions employed in his 

 experiments. 



In the life of QALVANI, in Bioo. Div. [see also VOLTA] there is an 

 account of the convulsive motions to which denuded frogs are subject 

 when the nerve and muscle form part of the galvanic circuit. In order 

 that an individual may receive a shock from a battery, it is advisable 

 to moisten the hand, because the dry cuticle is a bad conductor of 

 electricity : then, on holding one of the wires of the battery and 

 touching the other, the shock will be received and felt in the wrists, 

 arms, or shoulders, according to the intensity of the current ; or a 

 continued sensation, resembling the piercing of a very fine needle, will 

 be perceived by dipping the finger in a dish containing a little water in 

 which the wires of the battery are inserted at the same time with the 

 finger. In both cases, if the nerves are denuded by a cut, the sensa- 

 tion is painful, and the pain will remain some time before it subsides. 

 In some experiments of this kind Humboldt brought on an inflamma- 

 tion by applying the current to a cut. Volta has asserted that the 

 negative wire communicates the greater pain. 



A flash of light is perceived by covering the bulb of the eye with 

 tinfoil and forming a metallic communication thence with the mouth, 

 as for instance with a silver spoon ; also Berzelius found an acid taste 

 on dipping the tongue into a zinc vessel containing water, which was 

 placed on a silver stand, by touching the silver with his hand so as to 

 complete the circuit. When the negative current is communicated to 

 the taste, it is caustic and alk.iline. 



When the battery is applied to a nerve of a person recently dead, 

 and the circuit is completed, several violent motions ensue, dependent 

 on the relative position of the nerve and muscle ; thus, when the wire 

 communicates with the phrenic nerve, the muscles of respiration are 

 set in motion ; when from the ulnar nerve to the spiual marrow is 

 included in the circuit, the fingers are set in quick motion, and so on. 

 Fishes are still more susceptible of this electric action than animals, 

 and strong convulsive motions will be exhibited by a live flounder 

 placed on a zinc dish and having a piece of copper or silver on its back, 

 as goon as the two metals come in contact : similar effects take place 

 with leeches, worms, and amphibious animals. 



It was thought by Volta that the involuntary muscles, such as the 

 heart, could not be thus excited, but experiment has decided against 

 him. 



When the secretion was suspended by cutting the eighth pair of 

 nerves, Dr. Philip and several French anatomists have restored it by 

 establishing a galvanic current through the divided part of the nerves 

 next the stomach. 



Intermittent currents have been employed in the experiments of 

 Masson, Peltier, and Delarive. To effect this M. Masson used a toothed 

 wheel rotating by a cord round it ; its axis, supporter, and itself being 

 all metallic : a communication is formed between this wheel and a 

 battery in the form of a helix : the object of the teeth of the wheel is 

 occasionally to suspend the action of the current by making the con- 

 necting rod of too great a length ; hence, when the wheel is made to 

 revolve, the galvanic current acts and is suspended alternately. By a 

 series of intermitted discharges produced in this manner, M. Masson 

 had the cruel pleasure of killing a cat. 



It has been ascertained by Matteucci and others, that portions of 

 muscle and nerve present different electrical states with reference to 

 other portions of the same muscle or nerve. For example, the external 

 portion of a muscle may bear the same relation to the internal, as 

 platinum does to zinc in the voltaic circuit. In fact, a voltaic pile 

 may be formed by slices of muscle arranged so that the external part 

 of one slice may touch the internal part of the next, and so on. 



P. Santi Linari drew the electric spark from the gymnotua in the 

 following manner : he took a glass tube of the shape of a capital U, 

 which he partly filled with mercury ; at each end was fixed an iron 

 wire through a wooden button, and which reached very near the mer- 

 cury. The apparatus being fixed with mastic on varnished wood, the 

 ends of the wires were made to touch short platina wires terminated by 

 lamime of the same metal, intended to make a good communication 

 with the different parts of the electrical fish. When the circuit was 

 formed, a spark visible even in the daylight appeared at the placo 

 where the conductors were interrupted. This experiment he repeated 

 in different forms. (' Biblioth. Univ. de Geneve.') 



M. Delarive has noticed a remarkable difference of effects in tho 



