Chemical stability

“ Thus sulphur easily combines with the metals, oxygen, chlorine, or carbon, whilst gold and silver enter into combinations with difficulty, and form unstable compounds, which are easily decomposed by heat. The cause or force which induces the elements to enter into chemical change must be considered, as also the cause which holds different substances in combination—that is, which endues the substances formed with their particular degree of stability. ”

“ It is remarkable that among the most stable chemical compounds, we find combinations of atoms of one and the same element. Thus, the stability of the di-atomic molecule N2 is so great, that no trace of dissociation has yet been proved even at the highest temperatures, and as the constituent atoms of the molecule N2 must be regarded as absolutely identical, it is clear that “polar” forces cannot be the cause of all chemical action. ”

“ It is clear if organic bodies were built up of chemical compounds of small complexity and great stability that this continuous range of chemical reactions, this unceasing metabolism, could not take place. It is therefore a necessary condition for organic substances that they should be built up of chemical compounds that are most complex and unstable. “Exactly those substances which are most important for life possess a very high molecular weight, and consequently very large molecules, in comparison with inorganic matter. ”

“ Thus in all its aspects solution presents gradations from the most feeble affinities to examples of intimate chemical combination. The amount of heat evolved in the solution of equal volumes of different gases is in distinct relation with these variations of stability and solubility of different gases. 22·3 litres of the following gases (at 760 mm. pressure) evolve the following number of (gram) units of heat in dissolving in a large mass of water; carbonic anhydride 5,600, sulphurous anhydride 7,700, ammonia 8,800, hydrochloric acid 17,400, and hydriodic acid 19,400. ”

“ Oxygen and nitrogen, nitrogen and hydrogen, hydrogen and carbon, which show no affinity for each other under ordinary circumstances, readily unite when one or both are in a nascent condition. The reason seems to be that, when the elements of a compound are torn asunder, the chemical affinity which previously bound them together is set free, ready and eager to unite the nascent elements with whatever they come in contact with. ”

“ To destroy organic matter the most powerful oxidizing agents are required. We must boil it with nitric acid and chloric acid and the most perfect chemical agents. To think to get rid of organic matter by exposure to the air for a short time is absurd. ”

“ We know that, floating around us, these volatilized bodies exist in some material form, and numerous experiments in chemistry are calculated to convince us, that the most attenuated air is capable, with a slight change of circumstances, of being converted into the condition of solid masses. Hydrogen gas, the lightest, the most ethereal of the chemical elements, dissolves iron and zinc, arsenic, sulphur, and carbon; and from the transparent combinations thus formed, we can with facility separate those ponderous bodies. Such substances must exist in our own atmosphere ”

“ Thus, the rocks, earths, metallic oxides, water, carbonic dioxide, and nitrogen are extremely stable, and resist decomposition, or chemical union with other substances, with great energy. With regard to all substances this law holds good, that the tendency is to fall back from a less stable to a more stable condition, and that such a falling back is always attended with an evolution of heat; while, on the other hand, heat is always absorbed and disappears whenever the elements of a more stable substance are made to enter into a less stable condition. ”

“ The peculiar manner in which hydrogen gas appears to dissolve solid substances,—as iron, potassium, sodium, sulphur, phosphorus, selenium, and arsenic, may be explained by regarding the results as a manifestation of the powers of chemical affinity over the forms of bodies. In like manner, the solution of salt in water, or the mixture of alcohol in that fluid, may be viewed as chemical phenomena, although usually considered as simple cases of solution or mixture: alterations of temperature and other physical changes taking place in either. ”

“ Such an arrangement, if erected upon a scale sufficiently extensive, with the medium of a neutro-saline solution, would, in his opinion, produce large quantities of acids and alkalies with very little trouble or expense.
249 Alterations in chemical equilibrium are constantly taking place in Nature, and he thinks it probable that the electric influence, in its faculties of decomposition and transference, may considerably interfere with the chemical changes occurring in different parts of our system. ”

“ But however it may be with these acids, the peroxide of nitrogen and the perchloride of phosphorus evidently furnish us with the means of studying the laws of chemical equilibrium in gas-mixtures in which chemical change is possible and does in fact take place reversibly, with varying conditions of temperature and pressure. Or, if from any considerations we can deduce a general law determining the proportions of the component gases necessary for the equilibrium of such a mixture under any given conditions, these substances afford an appropriate test for such a law. ”

“ When oxygen combines with a single element, what is the compound called? We have found that O makes up a certain portion of the air; later, we shall see how large the proportion is. Its tendency to combine with almost everything is a reason for the decay, rust, and oxidation of so many substances, and for conflagrations, great and small. New compounds are thusformed, of which O constitutes one factor. Water, H2O, is only a chemical union of O and H. Iron rust, Fe2O3 and H2O, is composed of O, Fe, and water. The burning of wood or of coal gives rise to carbon dioxide, CO2, and water. ”

“ The view long maintained—until late in the nineteenth century, in fact—that organic and inorganic chemistry are separated from each other by a wide gap, is no longer held. Hundreds of organic substances, some of them of great complexity, have been made in the chemist’s laboratory, and can now be classed as properly with inorganic as with organic substances. The gap has been closed, and there is now but one chemistry. Only the most intricate chemical compounds still lie beyond the chemist’s grasp, and the isolation of these may be at any time overthrown. ”

“ It must not be understood that this force, which I finally came to control, annihilated matter; it merely annihilated form. Nor, as I soon discovered, had it any effect on inorganic structure; but to all organic form it was absolutely fatal. This partiality puzzled me at first, though had I stopped to think deeper I would have seen through it. Since the number of atoms in organic molecules is far greater than in the most complex mineral molecules, organic compounds are characterized by their instability and the ease with which they are split up by physical forces and chemical reagents. ”

“ But as soon as the solution is rendered stronger, or the solvent and the dissolved body are endowed with a mutual chemical affinity, chemical reactions set in. Part of the molecules of the dissolved body dissociate, and the atoms of which they were composed, on being set free, combine with the atoms of the solvent. Chemical forces, much more energetic than the physical forces, enter into play, and most complicated chemical reactions—the intensity of which may be judged of from the changes of temperature—begin. ”

“ To rapidly carry on the chemical action, the chemical agents should be well diffused and commingled throughout each other, and the blue lead should be so exposed as to be open to their attack on all parts of its surface equally, and all should be at, and kept at, a proper temperature and a proper degree of humidity. Too dry a heat prevents the process of conversion. Too moist an atmosphere wastes the materials and arrests their action. ”

“ May we not, therefore, conclude that the chemical action exhibited in a burning body is a development of some latent force, with which we are unacquainted, produced by the absorption of light;—that a repulsive action at first takes place, by which the hydrogen and carbon are separated from each other;—and that in the nascent state they are seized by the oxygen, and again compelled, though in the new forms of water and carbonic acid, to resume their chains of combining affinity? ”

“ It brings home to me what an unstable chemical compound man is. Here are the stage accessories as good as ever, while the players have all split up into hydrogen and oxygen and nitrogen and carbon, with traces of iron and silica and phosphorus. ”

“ Through solution, all soluble elements, which would otherwise remain locked in the inactivity of the solid state, are enabled to enter upon a new phase of mobility, of chemical life, as we may say. Only in water could colloid carbon compounds first be built up, and only from such substances could life originate. ”

“ This explains why salts are usually inactive and neutral in character, while acids and bases are active agents. Thus we see why the most positive or the most negative elements in general have the strongest affinities, while those intermediate in the list are inactive, and have weak affinities; why alloys of the metals are weak compounds; why a neutral substance, like water, has such a weak affinity for the salts which it holds in solution; and why an aqueous solution is regarded as a mechanical mixture rather than a chemical compound. ”

“ Although it may appear that some cases of chemical combination are due to these powers,—as, for instance, when the union of oxalic acid or sulphuric acid with lime produces an insoluble salt,—we cannot thus explain the constant proportions in which the metals, sulphur, oxygen, and similar bodies, unite. It is quite certain there is a power or principle, which we [Pg 286] have not yet reached, upon which are dependent all the phenomena which we now embrace under the term chemical affinity. ”

“ It was formerly supposed that the substances found in plants and animals, mostly complex compounds of carbon, hydrogen and oxygen, could only be produced by "vital forces." If this were true it meant that chemistry was limited to the mineral kingdom and to the extraction of such carbon compounds as happened to exist ready formed in the vegetable and animal kingdoms. But fortunately this barrier to human achievement proved purely illusory. The organic field, once man had broken into it, proved easier to work in than the inorganic. ”

“ To take a simple example:—oxygen and hydrogen are two gases which may be mixed in all proportions at ordinary temperatures, and it is easy to show that the properties of the products are simply those of mixtures of the two free gases. If, however, an electric spark be passed through the mixtures, powerful chemical union ensues, with its concomitants, great evolution of heat and consequent rise of temperature, and a compound, water, is formed which presents physical and chemical properties entirely different from those of its constituents. ”

“ When the body of a man, or of an animal, is exposed to the combined influences of air, of water, and of a moderately high temperature, it undergoes a series of chemical decompositions, whose final term is its transformation into carbonic acid gas, and some compounds, gaseous or solid, which represent the less advanced products of destruction. Gases of various kinds, carbonic acid, hydrosulphuric, and ammoniac, and the vapour of water, spread themselves through the atmosphere, or dissolve into the humidity of the soil. ”

“ Water, from its extensive powers as a solvent, never occurs in a state of absolute purity, although the nature and degree of its contamination must necessarily vary according to circumstances and situation. It is generally found holding earthy matter in a state of mechanical suspension, or saline and other bodies in chemical solution. ”

“ At higher temperatures the reaction always proceeds, at least in homogeneous systems, to a certain equilibrium, and as the chemical resistance now has finite values this equilibrium will always finally be reached after a longer or shorter time. ”

“ But this isn't all; for we must cool off the gas without causing the nitric oxide which has been formed to break up again into nitrogen and oxygen. To do this, we must call to our aid another chemical principle, which is this: although the quantity of a product finally formed in a chemical process sometimes increases and sometimes (as in this case) decreases with falling temperature, yet the rate at which that product forms or decomposes always decreases very rapidly as the temperature is lowered. ”

“ The heat given off accompanying the formation of a new compound is due to the increased activity of the component atoms produced by the action of the forces of the different substances, and the consequent increased influx of activity from the interior ether and aura into the new and more sensitive conditions. Where heat, electricity, or other agencies are necessary to produce the conditions for the operation of chemical affinity, it is due to the necessity of freeing the atoms from consolidated conditions that they may respond to the forces of attraction. ”

“ We have, in fact, the familiar act of combustion, and, as its consequence, the chemical union of the carbon or coal with the oxygen of the air, carbonic acid being the result. Here, then, we have a very powerful force acting only at a very small distance, which we name chemical affinity, inasmuch as it represents the attraction exerted between atoms of different bodies in contradistinction to cohesion, which denotes the attraction between molecules of the same body. ”