페이지 이미지

to them, and describing these ment. There are only a few cases, terms as the tools with which he however, in which the Chemists' worked. He then proceeded to art can reproduce the substances explain that all the changes which he has destroyed. Of these few, take place in the objects about us, water furnishes one of the most that are unaocompanied by sensi- striking examples. By analysis it ble motion, were the results of the is separated into oxygen and hyunion or separation of two or more drogen, and by synthesis this oxsubstances, which he characterized ygen and hydrogen are again formas unalterable elements. The ob. ed into water, The Chemist can, jects of Chemistry he explained to in many cases, reproduce bodies be an inquiry into the constituent with the same chemical, which elements of bodies, and to ascertain have not, however, the same me. the laws of chemical changes. Of chanical properties, All the bodies some substances the different na- of nature, of whatever description, tural properties (meaning the com- are composed of two or more of monly observed properties, we pre- the elementary substances; those sume) are found to be a correct in- only being called eleinentary suhdex to their different chemical pro- stances which the Chemists' art perties; of others the reverse is the has not decomposed; and this case. Thus charcoal or carbon art frequently proves that the differs as much in appearance as substances which are called elein its chemical properties from ments by one generation of Chepotash; butit differs stillmore in ap- mists, are by the next shown to pearance from the diamond, though · be compounds. Thus only a few its chemical properties are found years ago lime was regarded as a to be very nearly or precisely the simple substance ; but the experisame. To ascertain chemical pro- ments of Sir Humphrey Davy perties, two modes are had re- showed that it was a compound of course to. Or chemical researches metal, which he called calcium and are carried on both by analysis oxygen. Having thus shown to his and synthesis. Thus by applying audience the two modes of chemieither heat or a strong acid to mar- cal investigation, and explained ble, which, in the language of che- what was meant by a simple or mistry, is carbonate of lime, it is elementary substance, and enume. separated into the two substances, rated those at present known, the lime, and carbonic acid, each hav- Professor proceeded to sketch the ing very different properties from outline of the course he was to de. the marble. This is the analytical liver. We were not so fortunate mode of investigation. If the car as to comprehend exactly either bonic acid gas, disengaged from a the principles or the details of his piece of marble, is conveyed into a arrangements; but we understood solution of lime, the carbonic acid him to say, he should first explain gas unites with the lime, and again the laws of chemical action, and forms a substance, having the che- then treat of the simple substances mical, but not exactly the mecha. or agents, which are impondernical properties of lime. This is able, such as light, heat, and electhe synthetical mode of examina- tricity, and afterwards of those tion; and when the two modes which are ponderable. He then exactly correspond, chemical re- proceeded to explain and illustrate search is complete and correct. chemical action, The professor disengaged the car- Chemical action is produced by bonic acid gas from a piece of mar chemical affinity, and is known by ble, by the action of muriatic acid, the alterations which take place and he conveyed this same gas when two or more bodies are into a solution of lime-water, and brought into contact. The chemithere re-formed a carbonate, illus- cal action of two bodies is suppos. trating his doctrine by a very apa ed to be mutual and equal. Thus propriate and beautiful experi- when lime unites with muriatic acid, giving out its carbonic acid, glass tube to the mouth of each the affinity of the lime for the mu- flask, and he passed the other riatic acid is equal to that of the end of both into the opposite ends acid for the lime. The difference of a glass cylinder'; the heat of a between chemical affinity and cohe spirit lamp was then applied to sive affinity is, that the former ex the bottom of each flask, and the ists between the particles of dis- invisible vapour arising from the similar bodies, and the latter be- ammonia and from tho muriatic tween the particles of the same acid meeting in the glass cylinder, body. Thus the particles of iron became immediately white and are united into masses by cohesive flaky, so that the cylinder, from beaffinity, and the muriatic acid or ing transparent, was soon rendered carbonic acid combines with lime opaque, and there was found a by chemical affinity. Chemical white flaky substance deposited action is accompanied by several at the bottom. This substance remarkable circumstances; one of was sal ammonia. The Professor the most conspicuous of wbich is then illustrated chemical action, an alteration of temperature. Thus by the effect of air on iron; and hy mixing sulphuric acid and stated that when iron rústed, only water, such a quantity of heat is the oxygen of the atmosphere was given out, that ether boils by being absorbed, while the rust had hardly immersed in the mixture. The any of the properties of the metal; Professor mixed sulphuric acid that it was specifically lighter, bad and water, and plunged in it a no longer any lustre, and was not small glass tube containing ether, attracted by the magnet; he then which almost immediately boiled beautifully remarked that this rustup so as to be perceptible in every ing of iron must have been perceived part of the chapel. He then mixed from the earliest ages, and, if atsulphate of soda, we believe, with tended to, would have led to the nitrat of ammonia; the two com- discovery of the compound nature bined, and so great a degree of of the atmosphere, and not have cold was the consequence, that a' allowed this gem of science to have small portion of water contained remained undiscovered till the in a glass tube was frozen, to the cighteenth century. . Another ciradmiration of all the spectators. cumstance which frequently atHere, then, was the proof of change tends chemical action, is change of temperature accompanying che- of colour. Two pieces of copper mical action. But this is not the were plunged in nitric acid, which only accompanying circumstance, after a short time, became of a The sulphuric acid, diluted with deep blue, owing to the decompowater' that gave out heat, at the sition of the copper. Prussian blue same time diminishes in volume; so was precipitated by a mixture of that if measured after being mixed, two fluids that were almost colourthe combined substance would be less, which was an instance of a found to occupy less space than the coloured solid produced by mixtwo did when separate. This may ing two colourless fluids. A piece be considered as an approximation of indigo was plunged in a soto the solid form; and on the other lution of chlorine, and became hand, when the change is from perfectly colourless. This was a solidity to fluidity, cold is pro- good illustration of of the bleachduced. A change of form also ing power of this substance; and very generally accompanies che- Mr. Phillips remarked, that by inmical action. Fluids become solids, troducing it into bleaching, this and solids become fluids. Nay, operation was now performed in a even two imperceptible gases when few square yards, and but for this united form a solid. The Profes- discovery it would have required sor placed some volatile akali in as many acres. Chemical action or one flask, and muriatic acid in an. union is further accompanied by a other; he adapted one end of a total change of character, and

sometimes by a change which, on the contrary, the flash of the gun
prior to experience, it was impos- is seen even far beyond the range of
sible to imagine. Thus sulphuric the shot it hurls on a foe. We see
acid and potash, both dreadfully a vivid streak pass rapidly through
acrid substances, destroying our the clouds, but know not, till the
clothes and flesh, when applied to bolt falls on our houses, that it has
them, become, when united, sul- been accompanied by heat enough
phate of potash, a harmless, almost to melt iron. Light affects only
tasteless salt, and so little acrid the eye ; is imperceptible by any
that it is employed as a medicine. other organ; and, perhaps, the eye
Another circumstance which some is the only part of the body that
times accompanies chemical ac- does not convey to us the sensation
tion, was detonation; this effect of heat or cold. Heat and light,
the Professor showed by making therefore, are perfectly distinct;.
use of a small quantity of detonat- and fire, which in common lan-
ing silver; but this phenomenon guage signifies a union of both,
was one, which, from the danger should never, even for a moment,
of the experiment and of examin- be spoken of by scientific men as a
ing it, was not yet fully explained. simple or undecompounded sub-
The following, therefore, were the stance.
circumstances which he described We beg leare also to suggest to
as accompanying chemical action: Mr. Phillips, that chemical pro-

Change of temperature; perties are as much natural as any
Change of volume;

other properties. They are all naChange of form;

tural, and one part of the whole Change of colour.

ought not to be placed in contrast The subject, we understood, is to or opposition with the other. The be continued.

chemical properties of bodies are In conclusion we must observe, distinguished from their mechathat we are extremely well pleased nical properties, or from those that the Mechanics have obtained which are commonly and generally so able a Lecturer. Mr. Phillips is observed, as their weight, colour, distinct in his enunciation; he is and texture ; but both the mechaa neat and skilful experimenter, nical and chemical properties of and he was careful to repeat every bodies are equally natural. sentence which had the character Again, we are not quite clear as of an axiom. The zeal and at- to Mr. Phillips's distinction betention which his audience display- tween chemical aflinity and cohe-ed; the well-merited applause sive affinity. The former being.. they bestowed on various parts of according to him, the affinity behis discourse; and the repeated tween the particles of different sub clapping of hands which were heard stances; the latter, that power: at its close, must have convinced which combines the particles of him that his pupils were highly the same substance into massesdelighted, and that they merit his But copper and zinc are different care. For their sakes, we could substances; and, according to Mr. have wished that a more rigid logic Phillips's definition, should only had been observed by Mr. Phillips be sensible to chemical affinity : in bis division of the subject, and but they, as well as all the metals, in some of his expressions. In one when alloyed together, and many part of his Lecture, he spoke of other different substances, can exfire as a simple substance; and in ist combined together into masses. another, described light and heat, The very substance Mr. P. was which constitute fire, as distinct operating on should have dictated substances. That thcy are distinct a different, or at least a more cau. and separate, whether called agen- tious language. Carbonic acid cies or substances, is abundantly and lime are surely very different evident. The warm breeze from substances, but they exist comthe south brings no light with it; bined into masses. Nay, lime, when pure, assumes the character panied chemical action; he would of a powder; and it would seem now advert to some circumstances necessary, that the acid, or some which modify and control it. other different substance, should Heat, he showed, modifies it. be combined with it to give it so. Thus there are some substances lidity. Cohesive affinity is not, which have no effect on others, therefore, confined to the particles unless a considérable degree of of the same substance, but belongs heat is applied; when this is the also to the particles of different case, they decompose them. He . substances; and there is no ground illustrated this general fact by for the distinction which Mr. P., in several experiments, only one of imitation of other Chemists, laid wbich we can mention. Oxygen down.

and hydrogen gases were mixed • We make these few remarks in in the requisite proportion to form no spirit of hostility to this excel- water, but they had no effect on lent Lecturer, but merely to put each other till flame was applied him on his guard, that he may not to them, when they instantly combe led away by the slang of scien- bined, with a loud explosion, Antific men. It is incumbent on those other circumstance which modifies who téach, to do it honestly and chemical action, is the cohesion of conscientiously. They are liable, bodies. Nitric acid, for example, of course, like their scholars, and has no effect on adamantine spar, other men, to numerous errors; or common-pipe clay, both of which but they are bound, at least, to are nearly the same substance, think what they teach, to have an chemically speaking ; but if the honest conviction of its truth, and cohesion of these substances is denot to repeat, like parrots, the stroyed, as it is by their being words they may have heard. We combined with some other subshould make a much more rapid stance, then they will combine progress in knowledge, were those with nitric acid : thus showing who make it their business to in- that the attraction of cohesion struct us, only to give themselves modifies chemical action. Marble the trouble to examine the meaning is more quickly dissolved, if first of the words they repeat to us. reduced to powder, because a lar

ger surface comes in contact with SECOND LECTURE. the solvent. The same principle We attended the second Lec- explains why agitation promotes ture of Mr. Phillips, on Wednes- chemical action. A piece of blue day last, and are pleased that we vitriol, in water, coloured only the can say as much in praise of it, as water immediately above it, but by we have already said of the former. stirring it the whole water came in The Lecturer enters at once with turn in contact with it; the blue spirit into his subject, having vitriol was more rapidly dissolved, about him none of the dandyism and the whole of the water was of science, and desirous only freely coloured. It is sometimes the case and frankly to impart instruction. that the chemical action of two Referring to his former Lecture, he substances on one another does not said, he had partly explained che- take place without the addition of mical action, and had shown that a third. "Thus, for example, howno matter was lost. Combustion, ever water and oil may be agi. which appeared the consumption tated together, they do not comof a body, in fact, converted it into bine ; but add to them a solution a gaseous product; and it was pos- of an alkali, and they combine sible that the coal which we now immediately. Advantage has been consumed might hereafter return taken of this principle in many of to the same state, and by its re- the arts; and by means of it oil newed combustion warm future actually is united with water, and generations. He before explained forms the well-known and very the circumstances which accom: useful substance-soap, Another

circumstance which we shall state ciples, by numerous and plain exhere, though the Professor men: periments ; so that, we believe, tioned it later in the evening, which not one person could fail in commodifies chemical action, is voltaic prehending his meaning. At the electricity. Copper held in solu- conclusion, he announced his intion by an àcid, is not precipitated tention to touch briefly, in his enby silver; but if the silver be placed suing lecture, on the doctrine of in contact with iron in the solution, definite proportion, and on the thus forming a voltaic circle, cop- atomic theory. To the former we per is precipitated on the sil. have no objection: it can be made ver. The Professor then proceed. palpable without adopting the lata ed to illustrate the two great laws ter; and we would, therefore, enof chemical action, single and treat him to reflect before he indouble elective affinity. Thus volves us too deeply among im. nitric acid dissolves lime, iron, perceptible atoms. However he and copper; and this it does by may adopt the prevailing opinions single affinity; but it has a stronger on this subject, we are quite sure affinity for one of these bodies than he is a person of too good sense to for the others, and this is elective make theories of this nature à proaffinity. If 100 parts of nitric acid be minent feature in lectures for Me added to 100 parts of limé and 100 chanics. On the contrary, he shows parts of copper, it does not take 50 a disposition to teach them those of each, but unites with the whole principles which are applicable to of the lime, and leaves the copper the purposes of life; and one fact untouched. In consequence of sin which they can turn to account, is gle elective affinity, the Chemist is of more value to them than all enabled to produce single decom- the theories of Mr. Dalton and position. Lime precipitates cop- Berzelius. per from nitric acid by combining At the close of the Lecture, Dr. with the latter. But in double elec. Birkbeck announced, that Sir F. tive affinity, two compounds are de- Burdett had given the Institution composed, and two others formed. 100 guineas; and the Society of If sulphat of iron, a compound of Arts had presented it with a comsulphuric acid and iron, be added plete copy of their Transactions. to nitrat of lime, a compound of We are extremely happy to see nitric acid and lime, the lime se- the Institution thus increasing in parates from the nitric acid and wealth, as it goes on increasing the combines with the sulphuric acid, stock of information. while the nitric acid and iron form mitrat of iron. This principle of PROGRESS OF SOCIETY. double decomposition is not a mat. DURING the Lecture at the Meter of scientific curiosity merely; chanics' Institution, on Friday it is of essential use in the arts. se'nnight, Dr. Birkbeck told the By mixing sulphat of iron and tinc- following anecdote. He was disture of nut-galls, the calico-printer coursing of the elasticity of the forms his black-dye; and by à atmosphere, and showing that by similar operation ink is made. its pressure on the surface of Acetat of alumina is employed by fluids, they would rise only to a calico-printers; but acetic acid, or certain height. The principle by vinegar and alumina, cannot be which this fact was explained was made to combine directly. Alam, unknown to Galileo. The pumphowever, is sulphat of alumina; makers of Florence applied to him and a solution of this, added to know why the water would not to acetat of lead, precipitates rise higher than thirty-three feet, a sulphat of lead, while the ace- when the Grand Duke had comtat of alumina remains in solu- manded them to raise it upwards tion. This is what the calico- of sixty. Galileo believing that printers want, and this process is fluids only rose, at any time, on the what they actually perform. Mr. principle of nature, abhorring a Phillips illustrated all these prin- vacuum, answered that her abhor

« 이전계속 »