Imágenes de páginas
PDF

most recesses of things, and that he is equally active and present every where. The simplicity of the laws that prevail in the world, the excellent disposition of things in order to obtain the best ends, and the beauty which adorns the works of nature, far superior to any thing in art, suggest his Consummate wisdom. The usefulness of the whole scheme, so well contrived for the intelligent beings that enjoy it, with the internal disposition and moral structure of those beings themselves, show his unbounded goodness. These are the arguments which are sufficiently open to the views and capacities of the unlearned; while, at the same time, they acquire new strength and lustre from the discoveries of the learned.

The Deity's acting and interposing in the universe show that he governs as well as formed it; and the depth of his counsels, even in conducting the material universe, of which a great part surpasses our knowledge, keep up an inward veneration and awe of this great being, and dispose us to receive what may be otherwise revealed to us concerning him. It has been justly observed that some of the laws of nature now known to us must have escaped us if we had wanted the sense of seeing. It may be in his power to bestow upon ns other senses, of which we have at present no idea; without which it may be impossible for us to know all his works, or to have more adequate ideas of himself. In our present state we know enough to be satisfied of our dependency upon him, and of the duty we owe to him, the Lord and Disposer of all things. He is not the object of sense; his essence, and indeed that of all other substances, is beyond the reach of all our discoveries: but his attributes clearly appear in his admirable works. We know that the highest conceptions we are able to form of them are still beneath his real perfections; but his power and dominion over us, and our duty towards him, are manifest.

"Though God has given us no innate ideas of himself," says Mr. Locke, "yet having furnished us with those faculties our minds are endowed with, he hath not left himself without a witness; since we have sense, perception, and reason, and cannot want a clear proof of him, as long as we carry ourselves about us. To show, therefore, that we are capable of knowing, that is, being certain that there is a God, and how we may come by this certainty, I think we

need go no further than ourselves, and that undoubted knowledge we have of our own existence. I think it is beyond question that man has a clear perception of his own being; he knows certainly that he exists, and that he is something. In the next place, man knows, by an intuitive certainty, that bare nothing can no more produce any real being than it can be equal to two right angles. If, therefore, we know there is some real being, it is an evident demonstration, that from eternity there has been something: since what was not from eternity had a beginning, and what had a beginning must be produced by something else. Next it is evident that what has its being from another, must also have all that which is in and belongs to its being from another too: all the powers it has must be owing to, and received from, the same source. This eternal source then of all beings, must be also the source and original of all power; and so this eternal being must be also the most powerful.

"Again, man finds in himself perception and knowledge: we are certain then that there is not onlysome being, but some knowing intelligent being, in the world. There was a time then when there was no knowing being, or else there has been a knowing being from eternity. If it be said, there was a time when that eternal being had no knowledge; I reply, that then it is impossible there should have ever been any knowledge; it being as impossible that things wholly void of knowledge, and operating' blindly, and without any perception, should produce a knowing, being, as it is impossible that a triangle should make itself three angles bigger than two right ones. Thus, from the consideration of ourselves, and what we infallibly find in our own constitutions, our reason leads us to the knowledge of this certain and evident truth, that there is an eternal, most powerful, and knowing Being, which whether any one will call God, it matters not The thing is evident; and from this idea, duly considered, will easily be deduced all those other attributes we ought to ascribe to this eternal Being.

"From what has been said, it is plain to me, that we have a more certain knowledge of the existence of a God than of any thing our senses have not immediately discovered to us. Nay, I presume I may say, that we more certainly know that there is a God, than that there is any thing else without us. When I say we know, I mean there is such a knowledge within our reach

[ocr errors]

*mich we cannot miss, if we will but apply our minds to that as we do to several other inquiries ,

"It being then unavoidable for all rational creatures to conclude that something has existed from eternity, let us next see. what kind of a thing that must be. There are but two sorts of beings in the world that man knows or conceives; such as are purely material, without sense or perception; and sensible perceiving beings, such as we find ourselves to be. These two sorts we shall call cogitative and incogitative beings; which, to our present purpose, are better than material and immaterial.

"If then there must be something eternal, it is very obvious to reason that it must necessarily be a cogitative being; because it is as impossible to conceive that bare incogitative matter should ever produce a thinking intelligent being, as that nothing of itself should produce matter. Let us suppose any parcel of matter eternal, we shall find it in itself unable to produce any thing. Let us suppose its parts firmly at rest together; if there were no other being in the world, must it not eternally remain so, a dead (inactive lump? is it possible to conceive that it can add motion to itself, or produce any tiling r Matter then, by its own strength, cannot produce in-i(self so much as motion. The motion it has must also be from eternity, or else added to matter by some other being more powerful than matter. But let us suppose motion eternal too; but yet matter, incogitative matter, and motion could never produce thought. Knowledge will still be as far beyond the power of nothing to produce. Divide matter into as minute parts as you will, vary its figure and motion as much as you please, it will operate no otherwise upon other bodies, of proportionable bulk, than it did before this division. The minutest particles of matter repel and resist one another just as the greater do, and that is all they can do; so that if we suppose nothing eternal, matter can never begin to be; if we suppose bare matter without motion eternal, motion can never begin to be; if we suppose only matter and motion eternal, thought can never begin to be; for it is impossible to conceive that matter, cither with or without motion, could have, originally in and from itself, sense, perception, and knowledge, as is evident from hence, that then sense, perception, and knowledge, must be a property eternally inseparable from matter, quid every particle of it. Since, therefore,

whatsoever is the first eternal being, must necessarily be cogitative; and whatsoever is first of all things must necessarily contain in it, and actually have, at least, all the perfections that can ever after exist; it necessarily follows that the first eternal being cannot be matter! If, therefore, it be evident that something must necessarily exist from eternity, it is also as evident that that something must be a cogitative being. For it is as impossible that incogitative matter should produce a cogitative being, as that nothing, or the negation of all being, should produce a positive being or matter.

"This discovery of the necessary existence of an eternal mind sufficiently leads us to the knowledge of God; for it will hence follow that all other knowing beings that have a beginning must depend on him, and have no other ways of knowledge, or extent of power, than what he gives them; and, therefore, if he made those, he made also the less excellent pieces of this universe, all , inanimate bodies, whereby his omniscience, power, and providence, will be established; and from thence all his other attributes necessarily follow."

With respect to Christians, it need only be just mentioned, that they were very early divided in opinion as to the nature and essence of the Supreme Being; a great part worshipping three persons in the unity of the godhead, whilst others absolutely rejected a trinity of persons, and asserted the unity of the divine nature, both as to person and substance.

With respect to the theology of the Pagans, it is thought by most learned men that they acknowledged but one God ;*and that the many different divinities worshiped by them were but attributes and actions of one and the same God. This may probably be true of the wiser Heathens; and, indeed, there are many strong and beautiful passages in Pagan authors, to prove that these acknowledged but ope God. Thus Pythagoras taught the unity of God, and defined him to be a mind penetrating and diffusing itself through all the parts of the universe, from which all animals receive life; and Plato called God the being which is ; and whenever he mentions the Deity it is always in the singular number.

GOGGLES, in surgery, instruments used for the cure of squinting, or that distortion of the eyes which occasions this disorder. They an short conical tubes, composed of ivory stained black, with a thin plate of the same ivory fixed in the tables; through the centre of the plates is it small circular hole, about the size of the pupil of the eye, for the transmission of the rays of light. 'These goggles must be worn regularly and constantly, till the muscles of the eye are brought to act properly and uniformly, so as to direct the pupil straight forward.

GOLD is a yellow metal, of much greater specific gravity than any other body, in nature, except platina. It ir soft, very tough, ductile, and malleable; unalterable and fixed, whether exposed to the atmosphere, or to the strongest heat of furnaces. The most powerful burning mirrors are said to have volatilized it; and it has beeudriven

only one-twelfth part of the thickness of gold-leaf, though it still is so perfect as to exhibit no cracks when viewed by a microscope.

No acid acts readily upon gold but the nitro-muriatic acid, called aqna-rcgia, and the oxygenized-muriatic acid. The sulphuric acid, distilled from manganese, has some action upon it; as have likewise the pale nitric acid, and the phosphoric acid when boiling. Chromic acid added to the muriatic enables it to dissolve gold.

The small degree of concentration of which the oxygenized-muriatic acid is susceptible, and the imperfect action of the latter acids, render aqua-regia the most con

up in fumes, in the metallic state, by flame' venient solvent for this metal.

urged upon it by a stream of oxygen gas. The electric shock converts it into a purple oxide, as may be seen by transmitting that commotion through gold leaf between two plates of glass; or by causing the explosive spark of three or more square feet of coated glass to fall upon a gilded surface. A strong heat is required to melt it, which does "not happen till after ignition. Its colour, when melted, is of a blueish green; and the same colour is exhibited by light transmitted through gold-leaf.

The limits of the ductility and malleability of gold are not known, and its tenacity exceeds that of any other metal. A gold wire of one tenth of an inch diameter, requires 500/6. weight to break it.

The method of extending gold used by the gold-beaters, consists in hammering a number of thin-rolled plates between skins or animal membranes. By the weight and measure of the best wrought gold-leaf, it is found, that one grain is made to cover 56^ square inches ; and from the specific gravity of the metal, together with this measurement, it follows, that the leaf itself is' Tt^ parts of an inch thick. This, however, is not the limit of the malleability of gold; for the gold-beaters find it necessary to add three grains of copper in the ounce to harden the gold, which otherwise would pass round the irregularities of the newest skins, and not over them; and in using the old skins, which are not so perfect and smooth, they proceed so far as to add twelve grains. The wire which is used by the lace-makers is drawn from an ingot of silver, previously gilded. In this way,>from the known diameter of the wire, or breadth when flattened, and its length, together with the quantity of gold used, it is found, by computation, that the covering of gold is

VOL. Ill,

When gold is immersed in aqua-regia, an effervescence takes place with the escape of gas; the solution tinges animal matters ofa deep purple, and corrodes them. By careful evaporation, fine crystals of a topaz colour are obtained. The gold is precipitated from its solvent by a great number of substances. Lime and magnesia precipitate it in the form of a yellowish powder. Alkalies exhibit the same appearance j but an excess of alkali redissolves the precipitate. The precipitate of gold obtained from aqua-regia by the addition of a fixed alkali appears to be a true oxide, and is soluble in the sulphuric, nitric, and muriatic acids; from which, however, it separates by standing, or by evaporation of the acids. Gallic acid precipitates gold of a reddish colour, very soluble in the nitric acid, to which it communicates a fine blue colour.

Ammonia precipitates the solution of gold much more readily than fixed alkalies. This precipitate, which is ofa brown, yellow, or orange colour, possesses the property of detonating with a very considerable noise, when gently heated. It is known by the name of fulminating gold. The presence of ammonia is necessary to give the fulminating property to the precipitate of gold; and it will be produced by precipitating it with fixed alkali from an aqua-regia previously made by adding sal ammoniac to nitric acid ; or by precipitating the gold from pure aqua-regia, by means of sal ammonia, instead of the ammonia alone. The fulminating gold weighs one-fourth more than the gold made use of. A considerable degree of precaution is necessary in preparing this substance. It ought not to be dried but in the open air, at a distance from a fire, because a very gentle heat may cause it to explode. Several fatal accidents have Aa

arisen from its explosion, in consequence of the friction of ground stoppers in bottles containing this substance,'of which a small portion remained in the neck.

Fulminating gold, when exposed by Bertbollet to a very gentle heat in a copper tube, with the pncumatical apparatus of mercury, was deprived of its fulminating quality, and converted into an oxide at the same time that ammnniacal gas was disengaged. From this dangerous experiment it is ascertained, that fulminating gold consists of oxide of gold combined with ammonia. The same eminent philosopher caused ful-* initiating gold to explode in copper vessels. Nitrogen gas was disengaged, a few drops of water appeared, and the gold was reduced to the metallic form. In this experiment he infers, that the ammonia was decomposed; that the nitrogen, suddenly assuming the elastic state, caused the explosion, while the oxygen of the oxide united with the hydrogen of the alkali, and formed the water.

This satisfactory theory was still farther continued by the decomposition of fulminating gold, which takes place in consequence of the action of the concentrated sulphuric acid, of melted sulphur, fat oils, and ether; all of which deprived it of its fulminating quality, by combining with its ammonia.

Sulphurets precipitate gold from its solvent, the alkali uniting with the acid, and the gold falling down combined with the sulphur; of which, however, it may be deprived by moderate heat.

Most metallic substances precipitate gold from aqua-i egia: lead, iron, and silver, precipitate it of a deep and dull purple colour; copper and iron throw it down in its metallic state; bismuth, zinc, and mercury, likewise precipitate it. A plate of tin, immersed in a solution of gold, affords a purple powder, called the purple powder of Cassius, which is used to paint in enamel. There are various methods of managing this process. That described by Macquer consists in dissolving tin by very small portions at a time, without heat, in an aqua regia composed of two parts of nitric and one of muriatic acid, previously weakened with water equal in weight to both the acids. The first small portion of tin must be suffered to be entirely dissolved before a second is added. This addition must be continued till the acid has acquired a yellow colour, and scarcely acts at all upon the tin Lot added.

On the other hand, the purest gold must be dissolved in an aqua-regia, composed of three parts of nitric and one of muriatic acid. This solution may be made, as expeditiously as the operator chooses, by the assistance of the heat of a sand bath.

The solution of tin must then be largely diluted, as for example, with one hundred parts of distilled water; and a small quantity of this may then be assayed, by separating it in two parts, and diluting one of the parts still farther. Upon trial of both, by letting fall a drop of the solution of gold into each, it will be seen which affords the most beautiful purple precipitate. The whole of the solution of tin must accordingly be altered, if necessary, by adding more water. Pour into this solution, in a large glass or earthen vessel, nearly half as much of the solution of gold as it contains of solution of tin, stirring the mixture with a glass stick. In a short time the liquor will become of a beautiful red colour, which will gradually disappear on the subsidence of the precipitate. By adding a small quantity of the solution of tin, it will be seen whether the whole of the gold is precipitated. The clear liquor must then be decanted, and the precipitate washed. It consists of metallic gold and oxide of tin, at a maximum in combination, and is the only known substance which has the property of communicating a purple colour to glass. This purple powder is perfectly soluble in ammonia. Nitric acid boiled on it brightens it to a tint approaching that of cinnabar.

The difficulties attending the preparation of this article appear to depend on the state of the tin. If the solution of this metal be made with heat and rapidity, it becomes too much oxyded to adhere to the acid, or to precipitate the gold; and the combination of the two metals, which falls down, varies in colour according, as this term is approached: these are the chief circumstances; but there is no doubt that a complete examination of the process would indicate others worthy of notice.

Ether, naphtha, and the essential oils, take gold from its solvent, and form liquors which have been called potable gold. The gold which is precipitated by evaporation of these fluids, or by the addition of sulphate of iron to the solution of gold, is of the utmost purity.

In the dry way, gold resists the action of neutral salts, more especially nitre, which deflagrates with the imperfect metals.

i

\itre, however, does not afford air expeditious way of purifying gold, because this metal in some measure protects and covers the alloys from its action. It is remarked that borax, used as a flux with gbld, renders it paler; and that this alteration of colour disappears by the addition of nitre or common salt. As the acid of borax forms a compound with gold, which falls to the bottom when this acid is added to the metal in solution, it is probable that the paleness produced by borax may arise from the combination of a small portion of its acid with the gold, which might be driven off by a continuance of the heat, and united by stronger affinity with the alkali of the nitre, or of the common salt, in proportion as their acids are dissipated by heat.

Earths and alkalies do not act on gold in the dry way. Sulphur, which combines with most metals, has no effect on this. A process, called dry-parting, is grounded on this property; and is more especially used in separating silver from gold, when the quantity of the latter metal is too small to answer the expense of dissolving the larger mass of silver in nitric acid. For this purpose the mixed metal is fused, and flowers of sulphur thrown on its surface. These combine with the silver in the form of a black scoria, while the gold remains at the bottom in its metallic state.. The operation of dry-parting does not leave the gold in a state of purity; because the last' portions of silver are defended from the action of the sulphur. But when the quantity of silver is thus diminished the operation of parting with aqua-lbrtis, or nitric acid, may be advantageously used.

Sulphuret of potash dissolves gold in the . dry way. Equal parts of sulphur and potash are hastily fused with one-fourth of a part of gold leaf. This combination is soluble in water, with which it forms a yellowish green solution. By the addition of an acid the gold is thrown down in combination with the sulphur, of which it may be deprived by heat.

Most metals unite with gold by fusion. With silver it forms a compound, which is paler in proporti. n to the quantity of silver added. It is remarkable that a certain proportion, for example, a fifth part renders it greenish. From this circumstance, as well as from that of a considerable proportion of these metals separating from each other by fusion; in consequence of their different specific gravities, when their

proportions do not greatly differ it should seem that their union is little more than a mere mixture without combination ; for, as gold-leaf transmits the green rays of light, it will easily follow that particles of silver, enveloped in particles of gold, will reflect a green instead of a white light.

A strong heat is necessary to combine platina with gold: it greatly alters the colour of the gold if its weight exceed the forty-seventh part of the mass. Mr. Frangallon, however, informs us, that six parts of gold and one of malleable platina produce a metal of a beautiful colour, great malleability, susceptible of a fine polish, and more unalterable than gold itself. It does not much affect the ductility. The Spanish ministry has prohibited the exportation of platina from America, lest it should be used in adulterating gold; but this does not appear to be a danger which need be feared, as chemistry has long been in possession of several simple and expeditious methods of detecting this fraud, which besides is evident to the sight when the quantity of debasement is considerable. It may be questioned likewise whether the value of platina would not soon equal that of gold, if its properties and uses were better known in society. Gold made standard by platina, and hammered, is tolerably elastic.

Mercury is strongly disposed to unite with gold, in all proportions with which it forms an amalgam: this, like other amalgams, is softer, the larger the proportion of mercury. It softens and liquefied by heat, and crystallizes by cooling.

Lead unites with gold, and considerably impairs its ductility, one-fourth of a grain to an ounce rendering it completely brittle. Copper renders gold less ductile, harder, more fusible, and of a deeper colour. This is the usual addition in coin, and other articles used in society. Tin renders it brittle in proportion to its quantity; but it is a common error, of chemical writers, to say that the slightest addition is sufficient for this purpose. When alloyed with tin, however, it will not bear a red heat. With iron it forms a grey mixture, which obeys the magnet. This metal is very hard, and is said to be much superior to steel for the fabrication of cutting instruments. Bismuth renders gold white and brittle; as do likewise nickel, manganese, arsenic, and antimony. Zinc produces the same effect; and, when equal in weight to the gold, a metal of a fine grain is produced, which is said to be well adapted to form the mirrors ■A a 2

« AnteriorContinuar »