« AnteriorContinuar »
present state of our knowledge are best ex- have the strongest attraction for oxygen, are plained.
those which form the positive pole. But when v. The hypotheses, which have been framed to the fluid menstrua afford sulphur to the metals, account for the origin of the electricity, excited the metal, which under the existing circumby galvanic arrangements. And,
stances has the strongest attraction for sulphur, vi. A general view of the phenomena of determines the positive pole. Thus in a series electrico-magnetic motion, which, with the prin- of copper and iron plates, introduced into a porciples deducible from them, promise to throw celain trough, the cells of which are filled with light on some of the most interesting, but ob- water, or acid solutions, the iron is positive and scure operations of nature.
the copper negative; but when the cells are It will be for us to abridge the account of Dr. filled with solutions of sulphuret of potassa, the Henry.
copper is positive and the iron negative. When 286. It has been stated above, that electricity one metal only is concerned, the surface opposite is excited by friction ; but in Voltaic electricity the acid is negative, and that in contact with friction is not necessary. All that is required solution of alkali and sulphur, or of alkali is is the simple contact of different conducting positive. Elements of Chem. Phil
. p. 148. bodies with each other; and it has even been 291. Of Simple Galvanic Circles.—When a found by Dessaignes that two discs of the same piece of zinc is laid upon the tongue, and a metal, heated to different temperatures, give piece of silver under it, no sensation is excited sufficient electricity to excite contractions in the while the metals are kept apart; but immediately legs of a frog prepared for the purpose. Con- that you bring them into contact a metallic taste ductors of electricity have been divided into is perceived. This instance affords an example perfect and imperfect, the former comprehending of the arrangement of two perfect conductors, the metals plumbago and charcoal, the mineral which are the metals, with one imperfect one, acids, and saline solutions; the latter, or imper- the tongue, or rather the fluids which the tongue fect, including water, alcohol and ether, sul- contains. The metallic taste would seem to be phur, oils, resins, metallic oxides and compounds occasioned by the excitement of a small quanof chlorine.
tity of electricity, from the contact of the metals, 287. The least complicated galvanic arrange- and its action on the nerves of the tongue. ment, is termed a siinple galvanic circle. It 292. Compound Galvanic Circles, or Galvanic consists of three conductors, two of which must Batteries. The principle of these is the multibe of the one class, and one of the other class. plication of simple ones. Thus if, between a In the following tables, coustructed by Sir II. plate of zinc and of silver, a piece of moistened Davy, some different simple circles are arranged cloth, of the same size with these plates, be inin the order of their powers, the most energetic terposed, and brought into contact, a simple occupying the highest place.
galvanic circle is formed, as in the instance
above adduced; but if these be piled on each 288. Table of some electrical arrangements, other, in the order of zinc, silver, cloth, for wirich by combination form Voltaic batteries, several repetitions, we obtain a galvanic battery, composed of two conductors, and one imperfect termed from its discoverer the pile of Volta. The
power of such a combination is sufficient to give
a smart shock, as may be felt by grasping in the Zinc,
hands, which should be previously moistened, Each of these Iron,
two metallic rods, and touching with these the pole to all the
upper and lower extremity of the pile. The
Muriatic acid, Lead, metals below
shock may be renewed at pleasure, until after a Copper, it, and negative
Sulphuric acid, few hours the activity of the pile begins to abate,
Sal-ammoniac, Silver, with respect to
and finally ceases altogether. Gold,
Nitre, the metals a
293. The metals composing a galvanic battery
Other neutral salts. Platinum, bove it in the
may be more conveniently arranged in the form Charcoal. column.
of a trough; a happy invention of Mr. Cruikshank : in a long and narrow wooden trough,
made of baked wood, grooves are cut opposite 289. Table of some electrical arrangements, to, and at the distance of between one-third and consisting of one perfect conductor, and two three-quarters of an inch from, each other; and imperfect conductors.
into these are let down, and secured by cement,
square plates of zinc and copper, previnusly SOLUTION OF Copper, Nitric acid,
united together by soldering. The space, thereSilver, Sulphuric acid,
fore, between each pair of plates forms a cell for Sulphuret of Lead, Muriatic acid,
the purpose of containing the liquid, by which potassa, Tin,
the combination is to be made active. When Potassa,
containing acid. constructed in this way the trough affords an Other metals,
example of a galvanic combination of the first Charcoal.
kind (see the first table above), formed by two perfect, and one imperfect conductor. But it
admits of being modified, by cementing into the 290. In explanation of these tables, Sir H. grooves plates of one metal only, and filling the Davy, observes, that in all cases, when the Auid cells alternately with 'wo different liquids, as menstrua afford oxygen, those metals which diluted nitric acid, and solution of sulphuret of TOL. V.
is the positive Nitric acid,
potassa. In this case we have a battery of the the copper end be similarly connected, the jar is second order, formed by the repetition of one charged negatively. The shocks do not differ perfect and two imperfect conductors. See the from those of a jar or battery, charged to the second table above.
same intensity by a common electrical ma294. Other modifications of these galvanic chine. apparatuses will, as above intimated, be described v. Galvanism, even when excited by a single in the articles ELECTRICITY and GALVANISM. galvanic circle only, such as a piece of zinc, a Here it may be sufficient to add, using the words similar one of copper, and a piece of cloth, still of the author whom we are following, that moistened with a solution of muriate of ammoevery combination which is capable of forming nia, distinctly affects the gold leaf of the cona simple galvanic circle, may, by sufficient repe- densing electrometer. If the zinc end be tition, be made to compose a battery. The uppermost, and be connected directly with the combinations also which are most active in simple instrument, the electricity indicated is positive; circles are observed to be more efficient in com- if the pin of the electrometer touch the copper, pound ones.
the electricity is negative. A pile, consisting of 295. To construct a battery of the first order, sixty combinations, produces the effect still more it is essential that a fluid be employed which remarkably. exerts a chemical action upon one of the metals. vi. The chemical changes produced by galvanic Pure water, entirely deprived of air, appears to and common electricity, so far as they have hibe inefficient. In general, indeed, the galvanic therto been examined, are precisely similar. On effect is within certain limits proportioned to this last proposition it is necessary to dwell the rapidity with which the more oxidable metal more particularly, and, in so doing, we shall is acted upon by the intervening fluid. The still follow the author from whom, in the fluid generally used is nitric acid, with twenty present section, we have already so largely exor thirty times its weight of water. A battery tracted. which has ceased to be efficient has its activity 297. The most simple chemical effects, prorenewed by emptying the cells of their liquor, duced alike by the agency of electricity and and uncovering the plates : when the cells are galvanism, is the ignition and infusion of metals; filled with diluted nitric acid, the apparatus con- when, indeed, the galvanic power is excited to tinues active, even under the exhausted receiver a considerable extent, metallic wires may be igof an air-pump, or in an atmosphere of car- nited and fused, as is the case with a strong bonic acid or nitrogen gases. But if the cells electric battery; but, in the former instance, the be filled with water only, all action is suspended particles of the wire are not scattered to a by placing it under any of these circumstances. distance, as they are in the latter, since electricity Hence it appears that the oxidation of one or to act with greater violence than galboth of the metals composing the trough is vanism. Actual combustion, also, of metallic essential to the excitement of galvanic elec- wires may be effected both by electricity and tricity.
galvanism. 296. Are Galvanism and Electricity identical 298. But a much more remarkable action is powers ?—In adverting to, and discussing this exerted by the elective and galvanic fluids question, Dr. Henry points out the following in disuniting the elements of several combistriking resemblances :
nations. One of the first discoveries of the i. The sensation produced by the galvanic chemical agency of the pile, was its power of deshock is extremely similar to that which is excited composing water. Two piles of any metallic by the discharge of a Leyden jar. Both in- wire are thrust through separate corks, which are fluences also are propagated through a number fitted into the open ends of a glass tube, in such of persons without any perceptible interval of a way that the extremities of the wires, when the time.
corks are in their piaces, may not be in contact, ii. Those bodies which are conductors of elec- but may be at the distance from each other of tricity are also conductors of the galvanic fluid about a quarter of an inch. (galvanism ?) as the metals, charcoal, and a variety 299. If the parts of the wire which project of liquids. Again, it is not transmitted by glass, from without the tube, be made to communicate sulphur, and the whole class of electrics, which the one with the zinc or positive end, and the do not convey ordinary electricity. Among other with the copper, or negative end of a galliquids, those only are conductors of electricity vanic battery, a remarkable appearance takes and galvanism which contain oxygen as one of place. The wire connected with the zinc, or
positive end of the pile or trough, where it is iii. The galvanic fluid passes through air, and in contact with the water, if an oxidable metal certain other non-conductors, in the form of is rapidly oxidised, while from the negative wire sparks, accompanied with a snap or report; and, a stream of small bubbles of gas arises. But if like the electric fluid, it may be made to inflame the wires employed be of a metal which is not gunpowder, phosphorus, and mixtures of oxygen susceptible of oxidation, such as gold or.platina, ard'hydrogen gases.
gas is then extricated from both wires, and may iv. The Voltaic apparatus is capable of com- be separately collected. municating a charge to a Leyden jar, or even to 300. When a stream of galvanic electricity is a battery. If the zinc end of a pile, whether it made to act upon confined water, oxygen gas be uppermost or the contrary, be made to com- is given out at the positive end and hydrogen at municate with the inside of a jar, it is charged the negative end, and in the proportions which positively. If circumstances be reversed, and by their union compose water. At an early
S FE3 1971
period of the enquiry it was found, however, negative wire, and attracted by the positive one. by Mr. Cruikshank, that the water surrounding The flame of a candle, which consists chiefly of the positive wire became impregnated with a lit- ignited charcoal, when placed between a positive tle acid, and that round the negative wire with a and negative surface, bends towards the latter, little alkali,
but the flame of phosphorus, consisting chiefly 301. It was afterwards discovered, by Sir H. of acid matter, when similarly placed, takes à Davy, that the gases constituting water may be direction towards the positive surface. In the separately produced from two quantities of water case of neutral salts, the negative acid is atnot immediately in contact with each other ; this tracted by the positive wire, and the positively very important discovery evinced the trans- electrified alkali by the negative wire. ference of the elements of a combination to a 306. Thus then, continues our author, a considerable distance, through intervening sub- power has been discovered, superior in its energy stances, and in a forni that escapes the cognisance to chemical affinity, and capable either of counof our senses. But not only the elements of teracting it, or of modifying it according to cirwater but saline compositions and even metallic cumstances. The chemical attraction between salts were decomposed in the same way by Sir two bodies may be destroyed by giving one of H. Davy, the acid element of the salt being al- them an electric state, opposite to its natural ways collected at the positive, and the earthy one; or the tendency to union may be increased or alkaline one at the negative side of the ar- by exalting the natural electrical energies. rangement. Sir H. Davy even found that acids Further remarks on the theory of the galby galvanic excitation may be made to traverse vanic arrangement, and on the points on which opposite principles without combination, or be there is a seeming difference between Voltaic transferred through solutions of alkali, from the and common electricity, will best be discussed negative to the positive side, while on the other under the articles ELECTRICITY and GALVANISM, hand alkalis and metallic oxides were found to which we refer the reader. transmissable from the positive to the negative side, through intervening solutions of acids.
PART III, 302. These very singular and very momentous 307. Having thus investigated, to the extent discoveries rendered clear what before seemed of our limits, the general laws and principles of difficult of explanation, viz. why, by the agency chemical action, we are now to proceed in our of galvanism on water, alkali appears at the enquiries respecting the individual substances, negative and acid at the positive wire. Sir H. and their diversified compounds, the consideration Davy ascertained that all water, however carefully of which comes under the cognisance of chemical distilled, contains neutral salts in a state of solu- philosophy; indeed, the whole world of matter, tion. From these impurities the alkaline and acid as far as composition is concerned, lies before elements are separated, agreeably to a law which us; there is nothing with which, in a certain has already been explained. In the same way, way, the chemist has not to do; and, as far as also, the muriatic acid and alkali are accounted arrangement is concerned, we should now, had for, which some chemists have obtained by gal- we been writing but some few years since, have vanising what was before considered as pure adopted an arrangement of this vast mass of mawater; a fact which has been urged in proof of terials, something similar, if not quite the same, the synthetic production of both these bodies. as that pursued by Dr. Murray, in bis excellent Absolutely pure water, it has been demonstrated work. We should have proceeded to treat of by Sir H. Davy, yields nothing but hydrogen and atmospheric air, or at least have here referred oxygen gases. See HYDROGEN in the present the reader to that portion of the work in which
it is treated of; we should then have gone on to 303. Now it has been shown that ordinary the consideration of water, and its base ; to electricity, properly managed, is equal to the acids, their bases and composition; to alkalis, production of these curious decompositions; and with their bases; to earths, and their bases; it is fair to conclude, that galvanism and elec- metals, and their combinations; and thence into tricity are modifications of the same power.
the three great divisions of matter, mineral, ve304. A most important inference has been getable, and animal. deduced from the discovery of these facts, viz. 308. The very curious and extensively operathat hydrogen, alkalis, metals, and oxides, exist ting circumstances to which we have just rein a positively electrified state, and therefore will ferred at the end of the preceding section, have, be repelled by surfaces which are in the same however, given rise to a modification of these condition with themselves; that they will, on arrangements, founded on the principle that the contrary, be attracted by surfaces that are bodies are divisible into two great classes, viz. negatively electrified; and oxygen, as also the electro-negative, and electro-positive. Upon acids, in consequence of the oxygen they contain, such assumption is founded the division and being in a negative state, will be attracted arrangement which Dr. Henry adopts; and it by positive surfaces, and repelled by negative appears, to say the least, to have this in its fa
vor, that the student finds all along as he goes, 305. To apply this theory to the simplest more clear and decided illustrations of the magpossible case, the decomposition of water, the nificent discoveries of modern times, and has a hydrogen of this compound being itself positively better opportunity furnished him for appreciating electrified, is repelled by the positive wire, and these discoveries, and of applying them to their attracted by the negative one, while, on the con- respective purposes. trary, oxygen being negative, is repelled by the 309. This arrangement, therefore, we shall
likewise, to a certain extent, adopt, although it there is some want of precision in respect of may be open, as what artificial classification is their distinctive designations, but they are genenot? to some objections; it of course leaves rally known by their tendency to combine with untouched the animal and vegetable kingdoms, the acids, and by this union losing their indivior the materials of organic existence, which dual characters. See Alkali and Earth. therefore, as in other treatises, will fall to be 314. Oxide is a term applied to bodiss that considered separately, and after inorganic exis- have a less quantity of oxygen united to them tence shall have been disposed of. The objec- than that which is sufficient to produce acidity; tions which apply to the subdivisions, till recently these bodies may often be brought to the convery generally observed, of combustible and dition of positive acidity by causing them to non-combustible, will be best stated, because combine with more oxygen, and the loss of the most easily understood, as we proceed in our acidifying portion of oxygen may be again so investigations.
managed, and effected only in such quantity, as 310. ELECTRO-NEGATIVE Bodies.—Oxygen. that the acid shall be reduced to a state of This is only known as a separate principle in a oxide. gaseous state of existence, and even in this state 315. Chlorine. This substance was discovered it is combined with caloric; in the article Air by Scheele in 1774. It was named by the disseveral substances are mentioned as those from coverer dephlogisticated muriatic acid. In the which oxygen gas may be cbtained, and it is French nomenclature it was denominated oxythere stated, that the chlorate of potass yields it genated muriatic acid. It may be obtained in in the greatest purity. We have likewise given a gaseous form, by mixing black oxide of manin that paper the general character and habits of ganese with muriatic acid, and heating the mixoxygen, which need not be here repeated. ture over a lamp in a glass retort. The gas is
311. Oxygen was long supposed to be the soon evolved, and may be collected over warm only supporter of combustion, and in the La- water very conveniently; cold water soon abvoisierian theory it was treated of as essential to sorbs it. that process. It is now found, however, that 316. A mixture of eight parts of muriate of other bodies are equally entitled to rank as sup- soda, three of black oxide of manganese, four of porters of combustion, among which are chlorine sulphuric acid, and four of water will, if
proand iodine. The hypothesis of combustion pro- perly heated, evolve chlorine. posed by the French pliilosophers, has indeed 317. This gas has a pungent and disagreeable been found altogether unstable, both as it respects smell of a suffocating kind, and it is of a yelihe supposed necessity of oxygen for the pro- lowish green color, hence its name from xlwpos, cess, and its condensation, and as it endeavoured green. to explain the heat and light at times evolved. 318. It is heavier than common air; when Numerous are the instances in which oxygen, in dry it suffers no change by being subjected to
process of combustion, instead of being so- the most intense cold; but in its common state lidified, actually becomes gaseous during the it may be condensed into a liquid form, and, operation; the light, moreover, depends upon when exposed to a freezing temperature, the the combustible, and not upon the measure of aqueous part of the gas is deposited in the form oxygen consumed, and there are several cases of of crystals; this, however, is again taken up by combustion, as just intimated, in which no oxygen the gas upon the re-application of heat. is present. Combustion is much more probably 319. Chlorine is not altered by exposure to dependent upon the electrical conditions of very high temperatures. When it is suddenly bodies, and ought at any rate to be considered and greatly condensed, by mechanical pressure, rather as an intense chemical action generally, heat and light are evolved. Electricity does not than dependent, as Lavoisier conceived, upon a alter it. When a burning taper is introduced particular principle or form of matter. It will into a jar of chlorine, the flame becomes immebe inferred from what has been advanced above, diately red, a dense smoke is emitted from it, that all bodies acting powerfully upon each other and it is soon extinguished. But many bodies, are in the opposite electrical states, and heat such as phosphorus, and even several of the and light may be evolved as a consequence of metals, when finely powdered, are spontaneously the annihilation of these opposite conditions, ignited upon being immersed in chlorine, and occasioned hy their combination.
burn in it very brilliantly. The combustion in312. Substances capable of combining with deed of phosphorus in this gas is vehement. oxygen, afford one or other of the following 320. Chlorine is heavier than common air, products : 1. An acid. 2. An alkali, or earth, 100 cubic inches weigh 75.375 grains. or 3. An oxide.
321. It was once imagined, as may be inferred 313. We have already observed (see Acid) from its former names, to be composed of that ihe theory of Lavoisier, which regarded oxygen and muriatic acid. It is now treated of oxygen as the universal principle of acidity, is as a simple body; and the fact of its not being not consistent with more recent observations changed by electricity is in favor of this supand discoveries; but that acids are often the pro- position. duct of oxygenation will be seen as we proceed. 322. Chlorine and oxygen unite so as to form It is not easy, as we have before remarked, io oxides and acids. give very precise definitions of acids, since some 323. The euchlorine or protoxide of chlorine bodies have all the other characteristics of acids was discovered by Sir H. Davy; it may be obat the same time that they do not impart sour- tained by mixing muriatic acid with chlorate of ness to the taste : of the alkalis and earths too potass, and stirring the mixture with a platinum
knife; a yellow powder will be the result, which perchloric acid, which consists of chlorine and is to be put into a retort, and by means of a oxygen ; but it does not exist independent of water bath, the temperature of 150° applied; water, or a base. See. CHLORINE, in the body the oxide will pass off, and it may be collected of the work. over quicksilver.
329. IODINE.—This newly discovered sub324. Euchlorine when gently heated explodes, stance may be obtained from a solution of kelp expands, and becomes decomposed. Five parts or barilla, or from the ley of ashes of marine in volume become six, consisting of a mixture of plants, which furnish the mineral alkali. The oxygen and chlorine gases, in such proportions following process is given. Lixiviate powdered that euchlorine must be composed of two in kelp with cold water, evaporate the lixivium volume of chlorine, and one of oxygen, the till a pellicle forms and set aside to crystallize; latter being condensed into half its bulk, or by evaporate the mother liquor to dryness, and pour weight of
upon the mass half the weight of sulphuric acid.
Apply a gentle heat to this mixture in the Alask Chlorine
of an alembic, and fumes of a white color will Oxygen
arise and become condensed in the form of opaque crystals. The iodine first passes into the
receiver in the form of beautiful violet vapors, These proportions indicate that euchlorine is The crystals are to be quickly dried upon blot. constituted" of one atom of chlorine = 36, + ting paper. one atom of oxygen = 8, and hence its atom 330. Iodine was first discovered in 1812, by must weigh 44.— Henry.
M. Courtois, a manufacturer of saltpetre at Pa325. Combustion was in the Lavoisierian ris. Vauquelin, Gay Lussac, and Davy, have school, supposed to be necessarily attended with ably and fully investigated its properties. See a condensation of the bodies, which unite du- Annales de Chemie, 90th, 91st, and 93rd vols. ring the process; but the circumstances attending and the Philosophical Transactions for 1814. the decomposition of euchlorine by heat, viz. an 331. Iodine, like chlorine, is electro-negative, expansion of the elements, prove the hypothesis and therefore introduced here. It is solid at the not to be well founded.
ordinary temperature of the atmosphere, but ex326. What has been called deutoxide, or tri- tremely volatile, and at a temperature somewhat toxide, or with more propriety the Peroxide of under 80° emits a violet vapor. It produces Chlorine, is procured by triturating fifty or sixty a yellow stain upon the skin. It is sparingly sograins of the powdered chlorate of potass with a luble in water, much more so in alcohol and little sulphuric acid, so as to form a thick paste, æther. The color of the solution is yellow. The which is to be put into a retort and heated, but color of iodine is of a bluish black, its lustre is not to the boiling point. The gas may be received metallic, and its taste acrid. Its name is from over mercury. It has a lively yellow color, more wens, violaceous, on account of its vapor being brilliant than the euchlorine, and it is more ab- of a beautiful violet color. Its specific gravity sorbable by water. Its saturated solution in is = 4:946. water is of a deep yellow color, imparts an astrin- 332. Iodine combines with oxygen and with gent taste, and it may be kept unchanged in the chlorine, and by this combination produces two dark; the rays of light, however, decompose it acids which have been named lodic and Chloriand form from it chlorine and chloric acid.
odic. 327. Chloric acid.-Gay-Lussac, was the dis- 333. Iodic or Oriodic acid.- This compound cuierer of this compound of chlorine and oxygen; of oxygen and iodine cannot be obtained immeit is obtained by adding dilute sulphuric acid to diately, for iodine does not undergo change the chlorate of barytes; but this is a compound by being merely heated with oxygen, or even that exists only in the liquid state; and Sir 11. with chlorate of potass. It is, therefore procured Davy has even disputed the simple combination by the intervention of protoxide of chlorine. of chlorine and oxygen; he considers the liquid We may introduce iodine into a small fiask, and acid of Gay Lussac to be constituted of two disengage the chlorine oxide from it by a due adproportions, in the atomic composition of hydro- mixture of chlorate of potass; ‘or 100 grains of gen, one of chlorine, and six of oxygen. Underchlorate of potass may be introduced into a the word Acid the reader will find it stated, that small retort with 400 grains of liquid muriatic Dr. Murray has argued for the existence of hy- acid of the specific gravity 1:105; annex to the drogen as an acidifying principle generally, and retort a small globular receiver having a bent
mere constituent of the water with tube issuing from it, and passing to the bottom of which substances are combined; and this state- a small flask containing about fifty grains of ioment of Sir H. Davy, in reference to the compo- dine; carefully apply the heat of a lamp to the sition of the chloric acid, in some measure harmo- retort, by which oxide of chlorine will be disennises with that assumption,
gaged, and which will be decomposed and ab328. Perchloric acid.- in the process of ob- sorbed by the iodine. A compound is then formed, taining peroxide of chlorine a peculiar salt is which consists of chloriodic and oxiodic acids. formed, which was first noticed by count Stadion; The former is separable by a gentle heat, the latits taste is somewhat like the common muriate of ter remains as a white, semitransparent, sour, and potass. At the heat of 412° it is resolved into inodorous body, very soluble in water. It consists oxygen and muriate of potass, in the proportion of 117.7 iodine, 37'5 oxygen. (Brande). of 46 of the former to 56 of the latter. From 334. Todous acid.-Sig. Sementini procured a this salt sulphuric acid at 28° disengages the yellow fluid by distilling iodine and chlorate of
not as a