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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



21i* 



ON CHEMICAL AND ELECTRICAL FORCES, 

 By Pbofessob Fabadav. 



Professor Faraday has this season delivered a course of seven lectures at 

 the Royal Institution, " On the Allied Phenomena of the Chemical and Elec- 

 trical Forces." The last lecture of the course was given on Saturday, the 

 17th ult, and we now subjoin a brief sketch of the whole, showing the 

 mode iu which the subject was treated, and describing the principal expe- 

 riments by which it was illustrated. 



The first lecture was devoted entirely (o explanations of the character 

 and illustrations of the nature of chemical force, commencing with its 

 simplest forms. In the first place. Professor Faraday explained the dif- 

 ference between mechanical force, or the force of gravitation, which pro- 

 duces molecular action and aggregation of masses, and the action of 

 chemical force, which takes place among the particles of matter. At the 

 same time iis he entertains the opinion that all forces are closely allied, if 

 not identical, he showed several experiments in which chemical action is 

 eflected by mechanical force, of which the explosion of fulminating powder 

 by percussion afforded an example. The illustrations of chemical action in its 

 feeblest form, he showed to be closely allied to mechanical force, as the ag- 

 gregation of the particles of water, he said, depends on the same force as 

 the most energetic chemical action ; the dift'erence between them being 

 only in degree. As an illnstralion that chemical action takes place during the 

 mixing of fluids, he poured some spirits of wine gently on to the top of 

 ■water in a glass vessel, into which a long tube ivas inserted. The vessel 

 and the tube being quite filled, he inverted the apparatus, to mix the spirits 

 of wine with the water, when contraction in the volume of fluid was 

 manifest by the tube being no longer full. Among other exemplifications 

 of chemical action, were Ihe solidification of two gases (muriatic acid gas 

 and amraoniacal gas) on being mixed, and the conversion of two limpid 

 liquids (carbonate of potass and muriate of lime) into a white solid mass. 

 The results of chemical action, Professor Faraday observed, are the pro- 

 duction of compounds distinct from, and frequently quite dissimilar to, the 

 original substances that enter into combination. To show in a striking 

 manner the difl'erence between a mixture and a compound, he mixed to- 

 gether some copper and iron filings, and then separated the iron from the 

 copper by means of a magnet ; whereas in a chemical compound, no me- 

 chanical force can separate the combined particles, and they can only be 

 resolved into their original elements by the chemical action of some more 

 energetic agent. Though the original substances that enter into chemical 

 combination seem to be entirely lost in the resulting compound, yet there 

 is no destruction nor any alteration in the elements, nor is there any 

 creation or destruction of power produced by the combination. Professor 

 Faraday illustrated the reproduction of the elementary substance of a 

 compound after it had been apparently destroyed, in the following manner. 

 He put some iodine into a glass flask, which, on being heated, emitted the 

 purple or violet-coloured fumes peculiar to that substance. He then added 

 zinc and water to the iodine, when a combination took place, in which the 

 properties of the iodine were apparently lost, and by no application of 

 heat could the violet fumes be produced. On the addition of sulphuric 

 acid, however, the iodine was set free from its combination with the zinc, 

 and its fumes were again perceptible. That there is no destruction or 

 change in the particles of matter produced by chemical action is generally 

 admitted, but the Professor observed, that some philosophers still cling to 

 the notion that there is a creation of power, as exhibited in electricity ; 

 but this opinion, he maintained, is not founded on fact, for there can be no 

 creation of power without the creation of matter. 



In the second lecture the consideration of the difl'erent actions of chemi- 

 cal force was resumed in the commencement, and then its gradual transition 

 into electrical force was developed. In the first place, the Professor 

 pointed out the difference that exists between the force of gravitation and 

 chemical force in the relative constancy of their actions ; fur whilst gravi- 

 tation uever ceases to act at any moment, chemical affinity, on the contrary, 

 often lies dormant for ages, until circumstances arise that bring it into 

 action. Several experiments were performed to illustrate this, and also to 

 show that the results of chemical action may be reversed by varying the 

 temperature and the other conditions under which it takes place. A 

 mixture of nitrous and oxygen gases, for example, produces no change on 

 either litmus or turmeric paper, but when a stream of those mixed gases 

 issues into the atmosphere at the ordinary temperature, a piece of mois- 

 tened litmus paper exposed to the current is reddened, thus proving the 

 presence of an acid. When the same stream of mixed g«ses is heated, 

 the previously reddened litmus paper is restored to its original blue colour, 

 and turmeric paper is turned brown, showing that the directly opposite 

 property has been given to the gases, which then become alkaline instead of 

 acid. AV'hen approaching to those chemical actions which are ac- 

 companied by the development of electricity, Professor Faraday first ex- 

 hibited the solution of copper by an acid, and its reproduction in a metallic 

 form on pieces of iron and zinc, which metals having a greater attraction 

 for the acid that held the copper in solution than the copper itself, entered 

 into combination with the acid and liberated the copper. He afterwards 

 exhibited the action of oxygen and zinc, by first pouring some diluted sul- 

 phuric acid on a piece of that metal, which decomposed the water by at- 

 tracting its oxygen, with which it entered into combination, and liberated 

 the hydrogen as gas. On introducing a few shillings into the glass, the 

 vigour of the action increased, and the decomposing power of the zinc 

 seemed to be transferred to the silver, from which metal copious streams of 



hydrogen gas arose. A more obvious exhibition of the extension and 

 transfer of chemical action from one metal to another was effected by the 

 deposition of copper on silver from a solution of the sulphate of copper. 

 When a piece of silver is immersed alone in a solution of sulphate of 

 copper, no action whatever takes place, and it might so remain for any 

 length of time without sensibly decomposing the solution ; but as soon as 

 a piece of zinc or iron is brought in contact with the silver in the solution, 

 the copper is deposited on the silver as readily as on the zinc ; and when 

 the latter is amalgamated with quicksilver, the effects of decomposition are 

 transferred entirely to the silver, and none of the copper is deposited on 

 the amalgamated zinc. This effect is equally produced, whether the two 

 melals are brought into contact in the solution, or whether connection be- 

 tv/een them is made by a wire, through which the action is readily trans- 

 mitted. A new class of phenomena is brought into play by this exhibition 

 of chemical force in dissimilar metals. When the wire that connects the 

 two pieces of metal is made to pass over a suspended magnetic needle, the 

 needle in deflected on one side, and by expanding the surfaces of the 

 metals sufficient power is obtained to make a wire red hot. The deflec- 

 tion of the needle at any part of the connecting wire where it may be placed, 

 shows that the action occurs along the whole course of the wire, and exem- 

 plifies one of Ihe positions which the Professor wished to establish, viz., that 

 the distant and local actions are identical. This new class of phenomena. 

 Professor Faraday said, was, iu his opinion, attributable merely to another 

 exhibition of chemical force, but he should, in deference to received usage, 

 denominate it electrical force. 



The greater portion of the third lecture was occupied with the consi- 

 deration of the decomposing power of electricity, in which respect its 

 action seems the reverse of that of chemical force. The latter power acts 

 by the affinities of the particles of one substance for those of another, and 

 the results of its action are the formation of new compounds; electiical 

 force, on the contrary, resolves compound bodies into their elements, and 

 may act at a distance from its exciting cause. Numerous illustrations of 

 the decomposing power of the voltaic battery were afforded, one of the 

 most curious of which was the decomposition of muriatic acid by the 

 following arrangement : — A glass vessel was divided into three compart- 

 ments by diaphragms of blotting-paper, and filled with diluted muriatic 

 acid,— the acid in the two end compartments being coloured with indigo. 

 When the wires from the negative and positive poles of the battery were in- 

 serted in the two coloured divisions of the vessel, the muriatic acid became 

 decomposed, Ihe chlorine passing to one end, and the hydrogen to the 

 other ; which effect was rendered visible by the bleaching of the liquor in 

 the end to which the chlorine was determined, whilst the middle compart- 

 ment, through which the current force must have passed, remained un- 

 changed. The decomposition of iodide of potassium aflTorded a striking 

 example of the rapidity with which decomposition takes place under the 

 influence of electricity. Across a piece of paper, wetted with a saturated 

 solution of iodide of potassium. Professor Faraday drew rapidly one of the 

 wires from the battery, when a strong brown mark was left, showing that 

 the iodide had been decomposed. By pressing a coin on paper similarly 

 prepared, and then touching it instantaneously with the wire of the battery, 

 an impression of the coin was left on Ihe paper, caused by the decomposition 

 of the iodide where the parts most in relief had touched the paper. The 

 amount of decomposition is, in all cases, proportionate to the current force ; 

 and though chemical decomposition does not take place excepting when the 

 current is interrupted, yet the power is always active in its circuit through 

 the connecting wires. The deflection of a magnetic needle, when placed 

 parallel to the conducting wire, was adduced as a proof that the power 

 exerts an influence at every part of the circuit, and the plates of the vol- 

 taic battery were shown to have the same power as the conducting wire, 

 in deflecting the suspended needle from its ordinary position of north and 

 south. This current of force throughout was noticed by Professor Fara- 

 day as one of the many instances in which electrical force difl'ers in its 

 action from chemical force, which is always local, though the two forces 

 are really identical. The constant evolution of electricity, when we least 

 suspect the presence of such an agent, was curiously exemplified by cutting 

 a raw beef-steak with a steel knife and a silver fork, the knife and fork 

 being connected by wire."! with a voltameter. As soon as the knife touched 

 the meat, a current of electricity was evolved sufiicient to deflect the 

 needle of the voltameter. A cooked steak, peppered and salted, produced 

 a still more powerful effect on the needle. 



In the/oMr</i lecture the alliance between the chemical and electrical 

 forces exhibited in the evolution of light and heat, formed the principal 

 point to which the Professor directed attention, and he illustrated the 

 subject by numerous brilliant experiments. The light and heat produced 

 by violent chemical action, of which a burning candle is a good example, 

 form no essential part of the action that lakes place among the combining 

 particles, but are merely transient phenomena resulting from the activity of 

 the combination. In the same manner, the light and heat evolved during 

 combustion of substances by the voltaic battery, are the results of the com- 

 bination of the zinc plate with the oxygen of the exciting liquid. To ex- 

 hibit the voltaic light the lecture-room was darkened, and then pieces of 

 charcoal were exposed lo the action of the battery. The intensity of the 

 light thus evolved was contrasted with the flame of an argand lamp, which 

 was scarcely perceptible in the overpowering splendour of the voltaic 

 spark. The combustion of silver-leaf, of iron-wire, of platinum, and of 

 mercury, formed other dazzling exhibitions of the heat and light evolved by 

 the voltaic battery, when the two poles were brought into contact with the 



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