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the proposition by the analytical process. This chain of investi. gation is evidently so long, and of such flow formation, that we cannot, with any degree of correctness, appreciate the compara- . tive merits of those who severally extended it; nor point out the particular link upon which the grand discovery hangs. And the same distribution of praise is strictly proper in almost all the other instances of successful physical research. Even the composition of light was only unfolded by degrees, and appears to have been wonderfully nearly discovered by Grimaldi and others, with whose works Newton must have been acquainted. There are numerous proofs of such anticipations contained in the writings of Hookeand Mayow, as our chemical readers well know. Mr Robison has, in his notes to these lectures, pointed out several new and remarkable instances, more particularly from the works of the former. * The same obfervations may be extended to the most important discoveries in abstract science. The method of fluxions itself may be traced through a long fuccession of less elegant and less general inventions for finding quadratures and fubtangents.

But two great physical discoveries seem to have followed this law of continuity, in so flight a degree, that they may almoft be allowed to form a case of exceptions to its operation. These are, the universality of gravitation, and the combination of heat. As, before the time of Sir Isaac Newton, the influence of weight was only known by the falling of heavy bodies, all ideas of the attraction of gravitation were connected with this particular line of its operation: the only language in which men had ever learnt to express themselves upon the subject, was borrowed immediately from the particular case of vertical descent, and confined to the very limited sphere of its occurrence. In like manner, before the time of Dr Black, all the knowledge we had of the matter, or the motion of heat, was intimately connected with the idea of a fubftance, or a state, by which the sense of touch is affected in a specific manner, and the dimensions of bodies sensibly increased. The phlogiston of Stahl was evidently no inference from induction, even as modified and altered by his followers; neither was it the hypothesis of any peculiar qualities in the matter of heat : It was the assumption of a substance, different from every other with which we are acquainted, endued with qualities repugnant

to

* Note 13. Vol. I, contains a very interesting account of Hooke's theory of combustion. Its fimilarity to the antiphlogistic doctrine is iruly lingular ; and Mr Robisou is, so far as we know, the first writer who has remarked it. In p. 537, he says that he only observed it in 1798; but there must be some miltake in this ; for be published a no. tice of it is his valuable article Pneumatics, \ 37', Encyclopædia Bri. lannica, which appeared in the year 1795.

to the universal properties of matter, and capable of producing every effect which the inventors might with to explain. Phlogiston was indeed denominated the matter of heat and light ; buc it might as well have been called the reguline principle; and then, instead of saying that the escape of the matter of heat and light causes the calcinarion of metals, the followers of Stahl would have said, that the escape of the reguline principle causes the combustion of inflammable bodies. It is evident, that no specific effect, no subordination to the laws of chemical affinity, was ever ascribed to the substance which affects our sense with the feeling of heat, until Dr Black, from the most faithful and cautious examination of obvious facts, found, that this substance is capable of uniting with bodies, so as not to affect our senses with the pecu. liar feeling of heat, and yet to produce upon those bodies the most important changes--in the same manner that an acid, when combined with an alkali, ceafes to taste four, while it destroys the acridity of the alkali, and forms a third body, poffefsing the noxious qualities of neither. This physical law, discovered by the ftricteft induction, is applicable to the explanation of an infinite number of phænomena : its operations actually occur in almost every chemical experiment, and its influence is perceived in all the great processes of nature. For a most interefting detail of the Iteps by which Dr Black was led to the knowledge of it, we refer our readers to the first volume of these lectures. This narrative appears to us a model of philosophical writing, as well as of induction ; making allowance for the style of conversation, which is obviously adopted as most suitable for a public elementary lecture.

The other great discovery of Dr Black (the nature of the alka: line earths, and of fixed air) was scarcely less important in its con sequences to chemical science, than the one which we have been contemplaring. The account of it contained in these volumes, differs considerably from that which the author himself publithed. It dwells more minutely upon the steps of the investigation, and (with the exception of a few remarks upon borax, apparently copied from the treatise on magnesia alba and quicklime), it is compored in a style much less careful and finished than that which the Doctor seems to have employed when he wrote for publication.

Our readers will derive some entertainment from the compari. son; and we shall here.give, as a specimen of the manner which diftinguishes the whole of these lectures, the following paffage from the history of the discovery of fixed air. It unites, with great fimplicity of diction, an exemplification of. Dr Black's inimitable fimplicity and ingenuity in the contrivance of experiments.

. ...ri.... .: 'In • In the same year in which my first account of these experiments was published, namely 1757, I had discovered, that this particular kind of air, attracted by alkaline substances, is deadly to all animals that breathe it by the mouth and noftrils together ; but that if the noftrile were kept Ahut, I was led to think that it might be breathed with safety. I found, for example, that when sparrows died in it in ten or eleven feconds, they would live in it for three or four minutes when the noftrils were shut by melted fuet. And I convinced myself, that the change produced on wholesome air by breathing it, confifted chiefly, if not solely, in the conversion of part of it into fixed air. For I found, that by blowing through a pipe into lime water, or a solution of caustic al. kali, the lime was precipitated, and the alkali was rendered mild. I was partly led to these experiments by some observations of Dr Hales, in which he says, that breathing through diaphragms of cloth dipped in alkaline solution, made the air last longer for the purposes of life. *

o lo the same year, I found that fixed air is the chief part of the elastic matter which is formed in liquids in the vinous fermentation. Van Hela mont had indeed said this, and it was to this that he first gave the name gas silvestre. It could not long be unknown to those occupied in brew. ing or making wines. But it was at random that he said it was the fame with that of the Grotto del Cane in Italy (but be supposed the identity, because both are deadly); for he had examined neither of them chemically, nor did he know that it was the air disengaged in the effervescence of alkaline subítances with acids. I convinced myself of the fact, by going to a brew-house with two phials, one filled with distilled water, and the other with lime-water. 1 emptied the first into a vat of wort fermenting briskly, holding the mouth of the phial close to the surface of the wort. I then poured some of the lime-water into it, shut it with my finger, and shook it. The lime-water became turbid immediately. • 1 Van Helmont says, that the dunfte, or deadly vapour of burning charcoal, is the fame gas filvestre ; but this was also a random conjecture. He does not even say that it extinguishes flame ; yet this was known to the chemists of his day. I had now the certain means of deciding the question, fince, if the same, it must be fixed air. I made several indistinct experiments, as soon as the conjecture occurred to my thoughts; but they were with little contrivance or accuracy. In the evening of the same day that I discovered that it was fixed air that escaped from fermenting liquors, I made an experiment which satisfied me. Unfixing the nozzle of a pair of chamber bellows, I put a bit of charcoal, just red hot, into the wide end of it, and then quickly put. ting it into its place again, I plunged the pipe to the bottom of a

phial, . * In the winter 1764-5, Dr Black rendered a confiderable quantity of caustic fossil alkali mild and crystalline, by causing it to filtre dowly by ragę, in an apparatus which was placed above one of the fpiracles in the ceiling of a church, in which a congregation of more than 1500 persons had continued near ten hours.--Editor.

phial, and forced the air very flowly through the charcoal, fo as to maintain its combustion, but not produce a heat too suddenly for the phial to bear. When I judged that the air of the phial was completely vitiated, I poured lime-water into it, and had the pleasure of seeing it become milky in a moment.' Vol. II. p. 87. 88.

We cannot easily imagine a more interesting narrative; it reminds us of Montucla's admirable and animating account of the Torricellian experiment, with this essential differences that here the narrator was himself the performer of the action.

The following passage, from the concluding discourse on heat, may ferve as an example of Dr Black's powers of description ; and we cannot help regretting, that thefe volumes do not contain also the lecture in which he was wont (unnecessarily, indeed, but with great force of invective) to expose the manifold absura dities of Meyer's acidum pingue.

• It is plain, that not only all animal and vegetable life, but that the whole face and appearance of nature, the very form and powers of the clements themselves, depend on this limited action of heat. There are none of the elementary bodies with which we are better acquainted than water, Let us attend a little to the powers and qualities by which it acts its part in this system of beings. We all admire its pure transparency in a {pring; the level and polished surface with which it refle&ts objects that are on the banks of a lake; the mobility with which it runs along the channel of a brook, and the incessant motion of its waves in a formy (ca. But, when viewed with a philosophical eye, it appears much more an object of admiration. The same water which, under its usual form, is such a principal beauty in the scene of nature, is employed in her most extensive operations, and is necessary to the formation of all her productions. It penetrates the interior parts of the earth, and appears to affilt in the production of various minerals, stoges, and cartha, found there, by bringing their different ingredients toges cher, and applying them to one another properly, that they may concrete. We know it arises in vapours from the surface of the ocean, to form the clouds, and to descend again in rain upon the dry land, and give origin to springs, rivers, and lakes ; or, upon proper occafions, to form deep snow, which protects the ground and vegetables from the intense and mortal cold to which fome parts of the world are exposed ; and, after it bas performed this useful office, it readily yields to the heat of summer, and returns to a state in which it serves the same pur. poses as rain. By its fluidity and tenuity, it penetrates the soil, and the seeds of plants which that foil contains. These it causes to swell and germinate into plants, which depend on water for support. It pafles with freedom and cafe through all their minutcit tubes and ver. Eels, and carries with it materials necessary for nourishment and growth, or changes its appearance so as to become part of the plant... There is bo plant or vegetable substance, that does not contain in its composition a large quantity of water, cafily separable from it. The hardest woods contain a great deal. The softer and more succulent parts of vegetables are almoft totally composed of it. Even the oils and resinous substances can be resolved in part into water. It is plainly as necessary to the animals, and is found to be as copious an ingredient in the composition of their bodies, and of all the different parts of them. .. These are the numerous and extensive uses of this beautiful element. But, in this succession of forms and operations which it undergoes, you will perceive that it is set in motion, and adapted to these ends, by the nice adjustment and gentle vicissitudes of heat and cold, which attend the returns of day and night, and summer and winter; and that even the form, under which it and the other elements play their parts, depends on the limited action of heat. Were our heat to be diminished, and to continue diminished, to a degree not very far below the ordinary temperature, the water would lose its fluidity, and assume the form of a solid hard body, totally unfit for the numerous purposes which it serves at present. And, if the diminution of heat were to go ftill farther, the air itself would lose its elasticity, and would be frozen to a solid useless matter like the water ; and thus all nature would become a lifeless, filent, and dismal ruin. Such being the important part allotted to water, in the magnificent series of natural operations, in consequence of the qualities communicated to it by heat, all its properties become interesting objects of contemplation to a leofible heart." That peculiarity, by which the expansion and contraction of water by heat is distinguished from the same effect on other subftances, I mean its irregularity between 32° and 40° of Fahrenheit, naturally attracts attention. Even this seemingly trifling diftinction has been shewa by Count Rumford to have a mighty effect in rendering our habitation more comfortable. .. On the other hand, were the heat which at present cherishes and en. livens this globe, allowed to increase beyond the bounds at present pre. fcribed to it ; beside the destruction of all animal and vegetable life, which would be the immediate and inevitable consequence, the water would lose its present form, and assume that of an elastic vapour like air: the solid parts of the globe would be melted and confounded to. gether, or mixed with the air and water in smoke and vapour; and na. ture would return to the original chaos.' Vol. I. p. 245--247.

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Of the conversation style, in which these lectures are for the most part written, we may remark, that although it usually pof. fefies the advantages of plainness and fluency, yet, being adapted to the tones of the voice, it is very apt, when read over by a third person, to be deficient in perfpicuity; and being less premeditated, it is scarcely ever equal in precision to a good written Nyle. Its want of elegance is a defect of much less consequence; but all these circumstances must conspire to impair the effect of this work, unless the occasion of its composition be kept in view. ;

As a system of chemical instruction, the lectures of Dr Black poffefs very peculiar merits. Although they are, in many im. portant respects, of neceffity far behind the more recent systema

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