body to form a chemical combination with the oxygen, that is furnished by the supporters of the combustion; and so intimate is this union in many instances, that it is only with extreme difficulty we can again separate the oxygen from the oxide a Is it possible to separate entirely the oxygen from burnt bodies? Yes these compounds may be deoxidized in various ways; and in some cases the oxygen may be transferred from the burnt body to a fresh a When oil is burnt in an Argand's lamp, its carbon unites with the oxygen of the atmosphere, and forms carbonic acid gas; while its hydrogen unites with another portion of oxygen, and forms water. Every 100 ounces of oil thus burnt produce 130 ounces of water. In these products of combustion the oxygen is more intimately combined than it was with caloric in the gaseous state. Hence we see what a beautiful series of changes and modifications the elements of matter are destined to undergo, and how admirably Nature has provided for the preservation of all her productions. "To me be Nature's volume broad display'd; And to peruse its all-instructing page, My sole delight." That the combustion of alcohol produced water was known in the time of Boerhaave. By presenting a cold vessel to the flame of alcohol he collected water that was without taste or smell, and in every respect like distilled water. b. Water, as we have shown, is a product of combustion, and its base is hydrogen, the most combustible substance we are acquainted with. To restore the combustibility of the hydrogen, we have only to abstract its oxygen, which may readily be done by mixing iron or zinc filings, and sulphuric acid, with the water; by which means the metal becomes oxidized, and the hydrogen gas is evolved as combustible as ever. This may be adduced to show that the simple substances cannot be divested of their own peculiar properties by any of our mixtures, or even chemical combinations. combustible body, and be made the means of producing a fresh combustion; or it may sometimes be completely separated, and shown in its primitive or gaseous state a. What part of bodies is it which is destroyed by combustion? Νο part that we know of. We have reason to think that every particle of matter is indestructible, and that the process of combustion merely decomposes the body, and sets its several component parts at liberty to separate from each other, to form other new and varied combinations c. 2 This is frequently done for the purpose of procuring oxygen gas. The oxide of manganese, or of mercury, is exposed to a proper degree of heat, and the gas received in a suitable apparatus, as it is extricated. The following concise account of the theory of combustion I copy from Berthollet: "When bodies are burnt, none of their principles are destroyed; they had previously formed together one kind of compound, and they now separate from each other, at the high temperature to which they are exposed, in order to form others with the vital air in contact with them: such of the principles as cannot unite with the vital air, that is the earth, some saline and some metallic particles, compose the cinder. The new compounds formed, are carbonic acid, or fixed air and water: the proportion of these varies according to the proportion of the carbonic particles, and of the hydrogen that had been contained in the inflammable body.” Vol. i. p. 163. "It was said of old, that the Creator weighed the dust, and measured the water, when he made the world. The first quantity is here still; and though man 'can gather and scatter, move, mix, and unmix, yet he can destroy nothing: the putrefaction of one thing is a preparation for the being, and the bloom, and the beauty of another. Something gathers up all fragments, and nothing is lost."-Robinson. See Additional Notes, No. 37. What is the natural inference from this interesting fact? The natural conclusion is, that nothing less than consummate wisdom could have devised so beautiful a system, and that nothing short of infinite power could have so modified matter as to subject it to the operation of such laws; laws which · effect so many desirable purposes, and at the same time, so effectually prevent the destruction of those elementary principles, which are actually essential to the preservation of the world. a Perhaps it was in some such light as this that Pythagoras meant the metempsychosis to be understood. It might be a curious inquiry, whether or not he received this doctrine from the Egyptian priests, as they from the philosophers of India. An ancient Shastre, called the Geeta, has a beautiful stanza upon this subject, in which the varied form that nature assumes is compared to a change of dress. See Halhed's account of the Hindoo laws. Ovid, in the speech he forms for Pythagoras, compares it to wax, where the substance is always the same, though the outward form is varying. Dr. Darwin pursues the same idea in the following lines: "Hence when a monarch or a mushroom dies, CHAPTER XIII. OF ATTRACTION, REPULSION, AND CHEMICAL AFFINITY. WHAT is attraction? Attraction is that unknown force which causes bodies to approach each other 2. Which are the most obvious instances of attraction? The gravitation of bodies to the earth; that of the planets towards each other; and the attractions of electricity and magnetism ©. a Attraction has, by some philosophers, been attributed to an inherent property of matter, and by others to the influence of some foreign agent. The former is perhaps the most probable supposition. b Sir Isaac Newton demonstrated that the planetary attraction is the same principle as gravitation. To this principle we are indebted for the periodical flux and reflux of the tides, and for other important operations of nature. "For this the moon thro' heaven's blue concave glides, And into motion charms the expanding tides; While earth impetuous round her axle rolls, Exalts her wat'ry zone, and sinks the poles." FALCONER. For some account of magnetism see Note 2, page 317. In addition to that, it may be remarked that, if a steel needle be rubbed from its eye, to its point, a few times over the north pole of a magnet, and then stuck in a small cork, to swim on water; the eye will veer towards the north, and the point to the south. In this way the Chinese form their mariner's 393 Chap. 13.] ATTRACTION, REPULSION, &c. attraction? Yes: attraction subsists likewise between the particles of bodies; and it is this kind of attraction which comes under the more immediate cognisance of chemists b. How is this kind of attraction defined in chemical language? Whenever the force of attraction operates between particles of the same species, it is called the attraction of cohesion, or the attraction of compass; a guide on which they can rely at all times with perfect safety: "So turns the faithful needle to the pole, Tho mountains rise between, and oceans roll." DARWIN. * If common flowers of sulphur and potass be mixed and thrown into water, the sulphur will separate and the potass be dissolved; but if they be previously melted together, the union will then be so perfect, that the compound will be completely soluble. The design of this experiment is to show that chemical affinity has no sensible action but on the mere elementary particles of bodies. b All the operations of chemistry are founded on the force of attraction which nature has established between the particles of bodies, and by which force all bodies cohere. The art of chemistry employs different means to destroy this attraction of cohesion, and to form fresh substances by the means of new attractions. Take silex as an instance :-in this earth the attraction of cohesion is so strong, that the most powerful acids (one excepted) have no action upon it. But if the strength of this cohesion be broken by fusing it with an alkali, it then becomes obedient to some of the other acids, and may be held in solution by them. Klaproth found that the ruby and the adamantine spar are scarcely affected by any chemical agent; but that, if their cohesion be destroyed, they are then acted upon, and their ana Jysis can be accomplished. It is from the attraction of cohesion that a drop of water is |