Physical chemistry

“ The new branch of inorganic chemistry called physical chemistry has given us entirely new ideas of the nature of solutions, and the fact that electrolytes in solution are broken up into their constituent ions is one of fundamental importance. ”

“ AMONG the most significant advances in chemical theory are those relating to the action of heat on bodies. If we define chemistry, as I have been tempted to do, as that science which treats of the relations to one another of the different forms of mineral (i. e., unorganized) matter, and their transformations under the physical agencies of heat, light, and electricity, we shall see how difficult it is, in a sketch like this, to draw the line between physics and chemistry. ”

“ This short summary will suffice to show that attempts to discover relations between the physical attributes of substances and their chemical nature were made more or less sporadically from the time that chemistry was pursued in the spirit of science. But it is only in recent times that any great accession to knowledge has resulted from such efforts. The science of physical chemistry is practically a creation of our own period. ”

“ The more exact study of the physical phenomena of gases, and in particular the clearer recognition of the causes which determine the extent of their departure from the ideal gaseous laws, have afforded valuable assistance in ascertaining the atomic weights of certain elements independently of chemical considerations. ”

“ From a consideration of the chemical properties of the elements we shall now turn to an examination of the physical characteristics, although in a certain sense chemistry itself is but one special phase of physics.
If matter is really constructed of independently existing particles—atoms and molecules—the interplay of the individual parts must determine not only the chemical activities, but also the other properties of matter. ”

“ In the progress of physical science during the last twenty-five years, two principles have become more and more conspicuous, until at last they have completely revolutionized the philosophy of chemistry. In the first place, it has appeared that a host of chemical as well as of physical facts are coördinated by the assumption that all substances in the state of gas have the same molecular volume, or, in other words, contain the same number of molecules in a given space; and in the second place, it has become evident that the phenomena of heat are simply the manifestations of molecular motion. ”

“ Numerous phenomena of even a more striking character than those selected, are exhibited in every department of chemistry; but within the limits of this essay it is impracticable to speak of any beyond those which directly explain natural phenomena.
The chemical elements, which actually exist in nature as simple bodies, are probably but few. Most of the gases are in all probability compounds of some ethereal ultimate principles; and with the advance of science we may fairly hope to discover the means of reducing some of them to a yet more simple state. ”

“ As there is no doubt that the simple mechanical contact, or the action of heat alone, on substances sometimes causes an evident and always a latent (incipient) chemical change—that is, a different distribution or motion of the atoms in the molecules—it follows that purely chemical phenomena are inseparable from physical and mechanical phenomena. ”

“ From these experiments, both analytical and synthetic, we may now affirm that we have ascertained, with as much certainty as is possible in physical or chemical subjects, that water is not a simple elementary substance, but is composed of two elements, oxygen and hydrogen; which elements, when existing separately, have so strong affinity for caloric, as only to subsist under the form of gas in the common temperature and pressure of our atmosphere. ”

“ Observing in the physical and mechanical phenomena which accompany chemical reactions the quantity of energy manifested by the atoms and molecules, he is constrained to acknowledge that within the molecules there exist atoms in motion, endowed with an energy which, like matter itself, is neither being created nor capable of being destroyed. Therefore, in chemistry, we must seek dynamic equilibrium not only between the molecules, but also in their midst among their component atoms. ”

“ All the great speculative questions of modern chemistry must be eventually fought out upon the battle-field of physics.
Now, having recognized some facts concerning the intellectual future of chemistry, let us inquire what material steps will best lead up to them. What experimental work is most needed to begin with? Plainly, if we are to discover laws connecting the physical properties of compounds with their composition, we must first determine the physical properties of the elements. ”

“ In chemistry physical agents play important parts. By heat and light we cause atoms and molecules to unite or to fall asunder. Electricity exerts a similar power. Through their ability to separate nutritive compounds into their constituents, the solar beams build up the whole vegetable world, and by it the animal world. The touch of the self-same beams causes hydrogen and chlorine to; unite with sudden explosion, and to form by their combination a powerful acid. Thus physics and chemistry intermingle. Physical agents are, however, employed by the chemist as a means to an end ”

“ The theory of the atom and the molecule forms the second division of the work, this doctrine being tested and exemplified by the phenomena of refraction, polarization, magnetism, color, dissociation of gases, and the behavior of both colloids and crystalloids in solution. The transformation of matter and the transformation of energy are the two remaining division-, the former embracing the laws of chemical statics and chemical kinetics, while the latter is concerned mainly with thermo-chemistry, though touching upon the chemical action of light and electricity. ”

“ In fact, there are indications that the present theory of atoms and molecules of matter, as the foundation of chemistry, will at no distant day give place to a theory of chemistry based on the forms of energy, of which heat is a manifestation. ”

“ However large the masses changed by chemical action, that action is always on the individual molecule, the atoms of which are separated. If the molecule were an indivisible particle, no science of chemistry would be possible. The physicist finds the properties of masses of matter and resolves them into molecules, the chemist breaks up the molecule and from its atoms builds up other compounds. ”

“ When he found that each of the known elements, such as copper or oxygen or carbon, consisted ultimately of atoms, all the atoms of any one element being alike, he laid the foundation on which the huge structure of modern chemistry has been raised. The chemist takes one or more atoms of one element, one or more of another, and may be of a third or fourth, and he puts them together into a compound which we call a molecule. ”

“ Only a few constants have been determined for some of the most familiar elements, the gases especially. Just enough is known about the commoner metals to show us how ignorant we really are. Here, then, is a great field for work, and in it some of the richest materials for both chemistry and physics are to be gathered. ”

“ For example, the physicist determines the density, elasticity, hardness, electrical and thermal conductivity, thermal expansion, &c.; the chemist, on the other hand, investigates changes in composition, such as may be effected by an electric current, by heat, or when two or more substances are mixed. A further differentiation of the provinces of chemistry and physics is shown by the classifications of matter. ”

“ We have already pointed out the possibility of going through a course of physics without any special apparatus, we shall now endeavour to show our readers the method of performing some experiments in chemistry without a laboratory, or at any rate with only a few simple and inexpensive appliances. The preparation of gases, such as hydrogen, carbonic acid, and oxygen, is very easily accomplished, but we shall here point out principally a series of experiments that are not so much known. ”

“ Scientists talk of electrons and protons as the two elemental forces and of the mechanics of the atom. In chemistry, investigation follows the problems of applied chemistry, while organic chemistry or biochemistry opens continually new fields of research. ”

“ We now know that matter is not indefinitely divisible, and that the smallest parts of the various simple substances existing in those that are naturally compound have not all the same dimensions, nor equal weights. Chemistry, by a course of analyses and measurements, has succeeded in determining the weights of atoms of the different elements, that is to say, taking as a unit an atom of the lightest element, hydrogen, in determining the weight of the atoms which are equivalent to this conventional unit in the various combinations. ”

“ We also know that the total energy involved in any reaction is largely influenced by the surrounding conditions of temperature, pressure, and volume."
The interesting border-line between chemistry and physics is an increasing subject of research on the part of both the chemist and the physicist. The periodic press chronicles profound studies of the relations between chemical constitution and the phenomena of diffusion, of capillarity, of dialysis, of dissociation, and of the law of isomorphism. ”

“ Yet the doctrine that chemical ‘attraction’ and mechanical attraction are forces of the same kind has never, so far as I am aware, been worked out into a system of chemical theory; nor even applied with any distinctness as an explanation of any particular chemical phenomena. Any such attempt, indeed, could only tend to bring more clearly into view the entire inadequacy of such a mode of explanation. For the leading phenomena of chemistry are all of such a nature that no mechanical combination can serve to express them, without an immense accumulation of additional hypotheses. ”

“ These compounds, resolved into their elements by the processes of chemistry, yield a certain number (fifty-five) of substances which, under the conditions yet applied to them, are found to be incapable of further analysis, and are therefore called simple or elementary substances. They are singularly diversified in weight, mode of existence when separate, and relation to temperature and electricity.
In a free state under ordinary pressure and temperature, some (five) exist as gas; viz., hydrogen, oxygen, chlorine, fluorine, azote. Seven are non-metallic solids and liquids ”

“ The results which have been obtained in the examination of radio-activity, of kathode rays, of spectra at different temperatures, and of phenomena allied to these, bring again into prominence the ancient problem of the structure of what we call matter. Is matter fundamentally homogeneous or heterogeneous? Chemistry studies the relations between the changes of composition and the changes of properties which happen simultaneously in material systems. The burning fire of wood, coal, or gas; the preparation of food to excite and to satisfy the appetite ”

“ The study of the structure of molecules naturally leads to the study of their stability, and of the conditions which determine chemical changes, and thus opens the recently explored field of thermo-chemistry. To be able to predict the order and results of possible conditions of association of materials, or of chemical changes under all circumstances, is now the highest aim of our science, and we have already made very considerable progress toward this end. ”

“ The properties of matter are so distributed among the elements that three of them—Oxygen, Hydrogen, and Carbon—possess an ensemble of unique characteristics. The number of reactions in inorganic chemistry are relatively few, but in organic chemistry—in the chemistry of these three elements the number of different compounds is practically unlimited. ”

“ You know enough chemistry to realize that everything—water, air, food, all things which we use in every-day life—are merely combinations of certain simple elements. As you have seen me, by means of an electric current, decompose a jar of pure water into its two component parts,—two molecules of hydrogen to every molecule of oxygen,—so you can bring these same elements together in the gaseous state ”

“ The earth, and its surrounding envelope, the atmosphere, consist of a number of elements, which in myriad combinations give us everything we possess,—the air we breathe, the water we drink, the fire that warms us, are all made up of certain elements or gases. Water, hydrogen and oxygen; air, oxygen and nitrogen. Fire is combustion evolving light and heat. Chemical union always evolves heat, and when such union proceeds very rapidly fire is the result.
In all these combinations we shall find when we study chemistry that not a particle or atom of matter is ever lost. ”

“ Numerous considerations compel us to renounce the idea of statical equilibrium in molecules, and the recent yet strongly-supported appeals to dynamic principles constitute, in my opinion, the foundation of the modern teaching relating to atomicity, or the valency of the elements, which usually forms the basis of investigations into organic or carbon compounds. ”

“ If we examine carefully all the conditions of matter which we have made the subject of our studies, we cannot but perceive how gradual is the progress of the involved action of the physical forces, as we advance from the molecule—the mere particle of matter—up to the organic combination. At first we detect only the action of cohesion in forming the rude mass; then we have the influence of the crystallogenic powers giving a remarkable regularity to bodies; we next discover the influences of heat and electrical force in determining condition, and of chemical action as controlled by them. ”

“ By a law of chemistry there is the same number of molecules in a given volume of every gas, if the temperature and pressure are the same. Hence, all gaseous molecules are of the same size, including, of course, the surrounding space. They are in rapid motion, and the lighter the gas the more rapid the motion. This gives rise to diffusion. See page 114.
10. We Know Nothing Definite of the Form of Molecules.—In this book they will always be represented as of the same size, that of two squares. A molecule is itself composed of atoms,—from two to several hundred. ”