Chemistry

"The old mechanical and atomic hypotheses have, during recent years, become so plausible that they have ceased to seem like hypotheses; atoms are no longer just a convenient fiction. It seems almost as if we could see them, now that we know how to count them. ...The kinetic theory of gases has thus received unexpected corroboration. ...The remarkable counting of the number of atoms by Perrin completed the triumph of the atomic theory. ...In the processes used with the Brownian phenomenon, or in those used for the law of radiation, we do not deal directly with the number of atoms, but with their degrees of freedom of movement. In that process where we consider the blue of the sky, the mechanical properties of the atoms come into play; the atoms are looked upon as producing an optical discontinuity. ...The atom of the chemist is now a reality. But that does not mean that we have reached the ultimate limit of the divisibility of matter. When Democritus invented the atom he considered it as the absolutely indivisible element within which there would be nothing further to distinguish. That is what the word meant in Greek. ... the atom of the chemist would not have satisfied him since that is not indivisible; it is not a true element; it is not free from mystery, from secrets. The chemist's atom is a universe. Democritus would have considered, even after so much trouble in finding it, that we were still only at the beginning of our search—these philosophers are never satisfied. ...This atom disintegrates into yet smaller atoms. What we call is the perpetual breaking up of atoms. ...Each atom is like a sort of solar system where the small negative electrons play the role of planets revolving around the great... sun. ...the atom of a radioactive body is a universe within itself and a world subject to chance."

"The last thirty years have seen the beginning and development of a new period in physics and chemistry, namely the atomic period. In contrast to the period preceding it where nature's processes were described in terms of continua, recent developments have emphasized the discrete structure of the submicroscopic universe. Thus, today one hears of the atoms of matter, the atoms of electricity, and even the atoms of energy, the quanta. ...[T]he atomic theory of matter is the oldest and perhaps the most complete. ...[B]ecause of its relative simplicity the problem of the atomic theory of gases, in the form of the kinetic theory of gases, has attained the highest degree of perfection in this field. Its admirable methods of analysis are therefore indispensable... This book... endeavors to develop the various concepts... independently...Besides a simple introduction of each concept it gives derivations... elementary ones, using little or no calculus; more advanced classical derivations; and in some cases the most recent developments available. It also contains the comparison of the theoretical deductions with modern experiment and a critique of the theories."

"The science of Thermodynamics, founded by the labors of these three illustrious men [Nicolas Léonard Sadi Carnot, William Thomson & Rudolf Clausius], has led to the most important developments in all departments of physical science. It has pointed out relations among the properties of bodies which could scarcely have been anticipated in any other way; it has laid the foundation for the Science of Chemical Physics; and, taken in connection with the , as developed by Maxwell and Boltzmann, it has furnished a general view of the operations of the universe which is far in advance of any that could have been reached by purely dynamical reasoning."

"The first edition of this book appeared in 1877, at the time of the most rapid and beautiful development of the kinetic theory of gases. About twenty years before, the founders... Kronig and Clausius, had explained the expansive tendency of gases, and had calculated their pressure on the assumption that the smallest particles of gases do not repel each other, but are in rapid motion. From the theory based on this supposition not only were the laws of gases... deduced... but also new laws, hitherto undreamt of, were discovered... [and] afterwards confirmed... by experiment. These results, which we owe to Maxwell and Clausius, quickly won to the theory many friends and adherents. ...I undertook ...to exhibit the ...theory ...such ...as to be more easily intelligible ...especially to chemists and other natural philosophers to whom mathematics are not congenial. ...I endeavoured ...not only to develop the theory by calculation, but ...to support it by observation and found it on experiment. I... collected... and summarised, the observations by which the admissibility of the theory might be tested and its correctness proved. ...The mathematical discussions form ...an Appendix which ...need not be studied by every reader ..."

"The researches of Galileo, followed up by Huygens and others, led to those modern conceptions of Force and Law, which have revolutionized the intellectual world. The great attention given to mechanics in the seventeenth century soon so emphasized these conceptions as to give rise to the Mechanical Philosophy, a doctrine that all the phenomena of the physical universe are to be explained upon mechanical principles. Newton's great discovery imparted a new impetus to this tendency. The old notion that heat consists in an agitation of corpuscles was now applied as an explanation to the chief properties of gases. The first suggestion in this direction was that the pressure of gases is explained by the battering of the particles against the walls of the containing vessel, which explained Boyle's law of the compressibility of air. Later, the expansion of gases, Avogadro's chemical law, the diffusion and viscosity of gases, and the action of Crooke's radiometer were shown to be consequences of the same kinetical theory; but other phenomena, such as the ratio of the specific heat at constant volume to that at constant pressure, require additional hypotheses, which we have little reason to suppose are simple, so that we find ourselves quite afloat. In like manner with regard to light..."

"One of the most important and interesting aims of is to explain the properties of matter in terms of the motions and spatial arrangements of atoms and molecules. This aim has been more nearly achieved in the physical chemical study of gases at low pressures [below a few atmospheres at ordinary temperatures] than the study of matter in any other conditions. ... The structure of gases at these pressures is particularly simple: such gases are collections of molecules which move randomly in space and which collide with each other relatively infrequently—that is, the molecules are so far apart that much of the time they exert little influence on each other. ...[T]he properties of the gaseous state play a role in many important practical processes, such as [in]... the internal combustion engine, the function of the lungs, the motions of the winds across the earth and the flight of airplanes. Gases... provide a useful and pedagogically attractive starting point for the introduction of students to physical chemistry."

"It will be shown in this paper that, according to the molecular-kinetic theory of heat, bodies of microscopically visible size suspended in liquids must, as a result of thermal molecular motions, perform motions of such magnitude that these motions can easily be detected by a microscope. It is possible that the motions to be discussed here are identical with the so-called "Brownian molecular motion"; however, the data available to me on the latter are so imprecise that I could not form a definite opinion on this matter. If it is really possible to observe the motion to be discussed here, along with the laws it is expected to obey, then classical thermodynamics can no longer be viewed as strictly valid even for microscopically distinguishable spaces, and an exact determination of the real size of atoms becomes possible. Conversely, if the prediction of this motion were to be proved wrong, this fact would provide a weighty argument against the molecular-kinetic conception of heat."

"In 1909 Perrin suspended particles of in a liquid of slightly lower density, and found that the heavy particles did not sink to the bottom of the lighter liquid; they were prevented from doing so by their own Brownian movements. If the liquid had been infinitely fine-grained, with molecules of infinitesimal size and weight, every solid particle would have had as many impacts from above as below; these impacts, coming in a continuous stream, would have just cancelled one another out, so that each particle would have been free to fall to the bottom under its own weight. But when they were bombarded by molecules of finite size and weight, the solid particles were hit, now in one direction and now in another, and so could not lie inertly on the bottom of the vessel. From the extent to which they failed to do this, Perrin was able to form an estimate of the weights of the molecules of the liquid... and this agreed so well with other estimates that there could be but little doubt felt as to the truth either of the kinetic theory of liquids, or of the associated explanation of the Brownian movements."

"Now, although the plans of the edifice of the electromagnetic theory of light were laid in 1880 by H. A. Lorentz, and even indicated much earlier by W. Weber, a full 10 years were required before the discoveries of Heinrich Hertz gave the impetus to collect the building stones and work them into shape. In the years 1890-93 a number of works appeared by F. Richarz, H. Ebert and G. Johnstone Stoney, mostly dealing with the mechanism of the emission of luminous vapours, and in which attempts are made, on the basis of the kinetic theory of gases, to determine the magnitude of the elementary electrical quantity, called by Stoney by the now universally accepted name of electron. ...H. Ebert proved that the amplitude of an electron in luminous sodium vapour need only be a small fraction of a molecular diameter in order to excite a radiation of the absolute intensity determined by E. Wiedemann. The way of determining the amount of electricity contained in the electron is very simple. The quantity of electricity required for the electrolytic evolution of 1 cubic cm. of any monatomic gas is divided by Loschmidt's number—i.e., the number of gas molecules contained in 1 cubic cm."

"The kinetic theory of gases is a small branch of physics which has passed from the stage of excitement and novelty into staid maturity. ...Formerly it was hoped that the subject of gases would ultimately merge into a general kinetic theory of matter; but the theory of condensed phases... today, involves an elaborate and technical use of wave mechanics, and for this reason it is best treated as a subject in itself. The scope of the present book is, therefore, the traditional kinetic theory of gases. ...[A]n account has been included of the wave-mechanical theory, and especially of the degenerate Fermi-Dirac case... There is also a concise chapter on , which... may be of use as an introduction... [T]he discussion of electrical phenomena has been abbreviated... the latter voluminous subject is best treated separately. ...[F]undamental parts have been explained... [as] to be within the reach of college juniors and seniors. The... wave mechanics and statistical mechanics... are of graduate grade. ...[A] number of carefully worded theorems have been inserted in the guise of problems, without proof... to give... a chance to apply... lines of attack exemplified in the text. To facilitate use as a reference book, definitions have been repeated freely, I hope not ad nauseam. ...Ideas have been drawn freely from ...books such as ...of Jeans and Loeb..."

"It is difficult to understand the relative lack of progress in gas theory during the 18th century ...[T]here was little interest in the properties of freely moving atoms. The atoms in gas were... conceived as... suspended in the ether, although they could vibrate or rotate enough to keep other atoms from coming too close. This model was... awkward... mathematically, as... seen from an... attempt by Leonhard Euler in 1727. ...[O]ne contribution from this period has been... recognized as the first kinetic theory of gases. This is Daniel Bernoulli's derivation of the gas laws from a "billiard ball" model—in 1738... [H]is kinetic theory is... a small part of a treatise [Hydrodynamica (1738)] on hydrodynamics... Bernoulli's formulation and... applications of the principle of conservation of mechanical energy (...' ..."living force" ...) were ...more important than the fact that he proposed a kinetic theory ...a century ahead of its time ...Heat was still regarded as a substance ...Bernoulli's assumption that heat was nothing but atomic motion was unacceptable, especially to scientists interested in... radiant heat. The assumption that atoms could move freely through space until they collided like billiard balls... neglected the drag of the ether and oversimplified the interaction between atoms. ...When physics reached the stage of development at which the kinetic theory no longer conflicted with established principles, ...[it] had almost been forgotten and had to be rediscovered. ...In a very real sense, the man who persuades the world to adopt a new idea has accomplished as much as the man who conceived that idea."

"The influence of Quetelet's ideas spread throughout the sciences, even to the physical sciences. The two primary founders of the modern kinetic theory of gases, based on considerations of probability, were James Clerk Maxwell and Ludwig Boltzmann. Both acknowledged their debt to Quetelet. ...[H]istorians generally consider the influence of the natural sciences on the social sciences, whereas in the case of Maxwell and Boltzmann, there is an influence of the social sciences on the natural sciences, as Theodore Porter has shown."

"In this book I have tried... to make clearly comprehensible the path-breaking works of Clausius and Maxwell. The reader may not think badly of me for finding also a place for my own contributions. These were cited respectfully in Kirchhoff's lectures [on Maxwell's kinetic theory] and in Poincare’s Thermodynamique at the end, but were not utilized where they would have been relevant. From this I concluded that a brief presentation, as easily understood as possible, of some of the principal results of my efforts might not be superfluous. Of great influence on the content and presentation was what I have learned at the unforgettable meeting of the British Association in Oxford and the subsequent letters of numerous English scientists, some private and some published in Nature. I intend to follow Part I by a second part, where I will treat the van der Waals theory, gases with polyatomic molecules, and dissociation. ...Unfortunately it was often impossible to avoid the use of long formulas to express complicated trains of thought, and... to many who do not read over the whole work, the results will perhaps not seem to justify the effort expended. Aside from many results of pure mathematics which, though likewise apparently fruitless at first, later become useful in practical science as soon as our mental horizon has been broadened, even the complicated formulas of Maxwell’s theory of electromagnetism were often considered useless before Hertz’s experiments. I hope this will not also be the general opinion concerning gas theory!"

"Hari Seldon devised psychohistory by modeling it upon the kinetic theory of gases. Each atom or molecule in a gas moves randomly so that we can't know the position or velocity of any one of them. Nevertheless, using statistics, we can work out the rules governing their overall behavior with great precision. In the same way, Seldon intended to work out the overall behavior of human societies even though the solutions would not apply to the behavior of the individual human beings."

"Boltzmann decided to publish his lectures, in which the most important parts of the theory, including his ...contributions, were carefully explained. ...[H]e included his mature reflections and speculations on such questions as the nature of irreversibility and the justification for using statistical methods in physics. His Vorlesungen über Gastheorie was... the standard reference... for advanced researchers, ...[and] a popular textbook ...for the first quarter of the [20th] century ...The reason why the classical theory works is that, while the internal structure of molecules must be described by quantum mechanics, the interaction between two molecules can be fairly well described by a classical model which ignores this structure and simply uses a postulated force law whose parameters can be chosen to fit experimental data. ...Aside from phenomena at very high densities or very low temperatures, the only property that the classical theory fails to account for is the ratio of specific heats. ...Boltzmann ...simply concludes that for some unknown reason all the possible internal motions of a molecule do not have an equal share in the total energy, and takes this into account as an empirical fact."

"Boyle... proposed a theoretical explanation for the elasticity of air... "a heap of little bodies, lying upon one another"... The atoms are said to behave like springs... Boyle also tried the "crucial experiment" which was to help overthrow his own theory in favor of the kinetic theory two centuries later, though he did not realize its significance... Experiment No. 26... places a pendulum in the evacuated chamber... [A]bsence of air makes hardly any difference to the period of the swings or the time... to come to rest. In 1859, James Clerk Maxwell deduced from the kinetic theory that the viscosity of a gas should be independent of its density... which would be very hard to explain on the basis of Boyle's theory. ...Neither Boyle nor Newton claimed that the hypothesis of repulsive forces between atoms is the only correct explanation for gas pressure; both were willing to leave the question open. Boyle mentions the Descartes theory of vortices (1644)... somewhat closer in spirit to the kinetic theory since it relies more heavily on the rapid motion of the parts of the atom as a cause of repulsion. (Though Descartes did not believe in "atoms" in the classical sense.) Nevertheless, the Boyle-Newton theory of gases was apparently accepted by most scientists until about the middle of the 19th century, when the kinetic theory finally managed to overcome Newton's authority."

"These mystic alchemists interpreted the three principles in their own fashion. Mercury, the passive and female principle, was matter; sulphur, the active and male principle, was force; and salt, the middle term in the proposition, was movement, which applied force to matter. Or, expressed in another shape, mercury was the subject: sulphur, the cause; and salt, the effect. Symbolically, the theory was represented by an equilateral triangle, in one angle of which was the sign of sulphur or force; in the second, the sign of mercury or matter; and in the third, the sign of salt or movement."

"Aristotle had considered metals to be formed by the combination of moist and dry exhalations, and in the Jabirian works these... are... vapours of mercury and sulphur. The cause of the different metals was the... quality of the sulphur... The term sulphur ...as a component of metals probably referred to a volatile combustible material to which no... substance corresponded exactly. Likewise mercury... may... have been... an approximation to the other volatile liquid component of metals. ...The notion that metals contained a combustible principle persisted, and... provided the inspiration for the phlogiston theory."

"The Jabirian alchemists... believed that metals were ultimately composed of the four Aristotelian elements earth, water, air and fire... A base metal had to be treated with a medicine or elixir to adjust... qualities... with the proportions of gold. ...[Q]ualities of heat, cold, moisture and dryness could each be separated in pure form. ...First they subjected various organic materials to dry distillation... which often resulted in... a volatile combustible... (air), a liquid (water), a combustible tarry material (fire) and a dry residue (ash). [Each of] [t]hese elements were supposed... composed of two qualities, and... could be isolated by... purification. Thus water... could be converted into pure cold by repeated distillation... and further [distillations] in the presence of a drying agent. The resulting pure cold... a brilliant white solid."

"Paracelsus made an important contribution to chemical theory. He extended the sulphur-mercury theory of the Islamic chemists by adding a third principle... salt. Thus, when wood burned, the combustible component was identified with sulphur, the volatile component with mercury and the ashes... with salt. The composition of all substances could be expressed in terms of these three principles, or tria prima. As in previous theories... [these] were not... common materials... but rather... essential qualities."

"These general considerations are sufficient to convince us, that in nature a substance exists whose properties are different from those of fire, air, water; and which is, like these other substances, one of the elements of compound bodies. But a vague assertion like this does not satisfy chemists. Besides the ascertaining of the exigence of the different substances submitted to their examination, they require to know the properties of these substances in their greatest degree of purity and simplicity; but they have found much difficulty and uncertainty in investigating the essential properties of the purest and simplest terrestrial element."

"What made silica so interesting was that... it did not seem to follow the established rules of chemical combination. In Smithson's time, chemical combination was... an acid combining with an alkali to produce a stable, neutral... "." Acids did not combine chemically with each other, nor did alkalis... [A] substance... found to contain an alkali... must also contain an acid—and vice versa. Bergman's description of the compounds containing earths as... "natural compositions of acids" meant... the other component must be alkaline—which the earths all seemed to be, except for silica."

"Earth is not found so pure as the other elements, fire, air, and water, which, though not entirely free from mixture, are however so pure, that we may certainly and easily discover their fundamental properties. These properties of each of these pure elements are so well ascertained, and so evident, that nobody has yet attempted to distinguish different kinds of fire, air, or water, notwithstanding the differences which may arise from the heterogeneous substances with which they are almost always mixed."

"Earth is one of the four simple substances called elements, or primitive principles; because they are indeed the most simple of all those which enter into the combination of compound bodies. We cannot doubt, in particular, that the greatest part of the compounds which we can analyse contain earth as one of their principles; for after art has exhausted all its efforts to decompose them, a fixed and solid matter always remains, upon which no change can be produced; and this is what is generally called earth. It has the solidity, weight, fixity, and other principal properties of the mass of solid matter which forms the globe we inhabit, called also the earth."

"Lithia is much less soluble in water than the other alkalis."

"The solid alkalis are not decomposed by the action of heat alone."

"The most general and most probable opinion is, that as only one kind of fire, of air, and of water, so only one kind of simple elementary earth, exists. Alchemists chiefly have endeavoured to discover this primary earth, not with an intention to ascertain its properties, but because they imagined that as gold is the purest of metals, the earth of which it is partly composed must be also the most pure; they have, therefore, searched every where for this earth, which they call pure earth and virgin earth. They have endeavoured to obtain it from dew, rain, the air, ashes of vegetables, animals, and several minerals: but it was impossible to find it in compound bodies; for we shall see that when once this element makes part of a compound body, it cannot be disengaged from the substances with which it has united."

"By 3000 BCE the Sumerians, perhaps while heating copper to make it more malleable, had discovered that more copper could be retrieved from the fire if the metal were heated with certain types of dirt and stones—that is, certain earths. These earths were the metal s, and the process they discovered, ', reduced metal salts to pure metal by the action of in the fire. The process of changing metal salts into pure metal is known as reduction because the metal without the accompanying oxygen, , or of the salt weighs less than the ore. Eventually metal workers learned to distinguish various metal-bearing ores by color, texture, weight, flame color, or smell when heated (such as garlic odor of ores) and they could produce a desired material on demand."

"When moist, the alkalis, with the exception of , readily combine with to form s."

"Pliny recorded processes involving metals, salts, , glass, mortar, soot, ash, and a large variety of s, earths, and stones. He describes the manufacture of charcoal; the enrichment of the soil with lime, ashes, and manure; the production of wines and ; varieties of s; plants of medicinal or chemical interest; and types of , gems and precious stones. He discusses some simple chemical reactions... and a crude indicator paper... of strips soaked in an extract of oak galls that changed color when dipped in solutions of blue vitriol... contaminated with ."

"Alkalimetry. ...The object of alkalimetrical operations is to determine the quantity of caustic alkali, or of carbonate of alkali, contained in the potash or soda of commerce. These operations are simple, accurate, rapid, and easy; they may be said to consist in pouring on a weighed portion of the sample of potash or of soda under examination, a certain quantity of an acid of a known strength, until the alkali is saturated, that is to say, until the neutralizing point is hit, which is ascertained by means of ..."

"The alkalis are very soluble in water; these solutions neutralise acids forming salts, and also precipitate most of the heavy metals from their solutions in the form of oxides or hydrated oxides; aqueous solutions of the alkalis act corrosively on animal and vegetable substances, and also alter the tint of many colouring matters."

"But we cannot say the same of earth; for a considerable number of substances are called earths, because they possess the principal properties of the terrestrial element: but these substances, when examined more particularly, are always found to differ from each other so much in other respects, and to be so difficultly purifiable from heterogeneous matter, that we have not ascertained whether only one simple and elementary earth, or several ones essentially different, although equally simple, exist."

"The Earths are white, inodorous, tasteless, and uninflammable substances—non-conductors of electricity, insoluble in water, but soluble in one or more of the acids. Sp. gr. compared to that of water, not exceeding five to one. They are six in number; viz. silica, alumine, , gluttine, augustine, ytria; the consideration of which falls under their alphabetical order."

"It was taught by some chemists that an alkali is hidden in every earth, and by others that an alkali is an earth refined by the presence of acid and combustible matter. Black's exact quantitative investigations tended to disparage all such explanations as these; but it yet remained to find the precise composition the alkalis and the earths."

"Lavoisier thought that these bodies must be compounds; but, as he had no means of proving this, he classed them with the elements, while suggesting that the earths were probably compounds of oxygen with unknown metals."

"In 1807 Davy decomposed two alkalis, and soda, by passing an electric current through these substances when molten; and a year later he succeeded, by the same agency, in separating the earthy bodies lime, baryta, and strontia, into oxygen and, in each case, a metal."

"Closely allied to, and sometimes regarded as identical with, the alkalis, was the group of earths. These bodies were known to neutralise acids and affect colouring matters like alkalis, but they were much less soluble in water than the alkalis."

"The notion of (end of 15th and beginning of 16th century), that lime when burnt combined with 'matter of fire,' had been accepted by many as an explanation of the difference in the behaviour towards acids of burnt and unburnt lime. If this explanation applied to magnesia it should be possible perhaps to get hold of this 'matter of fire,' which combined with the magnesia alba when that body was heated. But Black found that a given mass of magnesia alba weighed more than the calcined magnesia obtained from it. Hence something was lost instead of gained during the process of heating. This something proved on further quantitative examination to be a gas different from common air; to it Black gave the name of fixed air."

"The effervescence or non-effervescence of alkalis with acids was proved by Black to accompany the presence or absence of fixed air (). From this time a distinction was clearly drawn between alkalis, which dissolved in acids without effervescence, and carbonated alkalis, the solution of which in acids was accompanied by the escape of carbonic acid gas. It was recognised that whether a caustic or a carbonated alkali dissolved in an acid, the body which remained in solution, and which had no close resemblence either to the acid or the alkali, was one and the same."

"The name alkali is now generally applied to the compounds of and oxygen with one or other of the five metals, , , , , cæsium (v. Alkalis, Metals of the); an aqueous solution of is also regarded as containing an alkali, viz. a compound of hydrogen and oxygen with the radicle ' (v. Ammonium Compounds)."

"The properties of the alkalis were supposed by the older chemists to be due to a 'principle of alkalinity,' or sometimes to a 'principle of saltness,' which latter principle was common to acids, alkalis, and the products of their mutual action, i.e. salts."

"Besides being built on the bases of alkalis and earths, salts could be formed by adding s to the calces of metals. When Lavoisier had proved calces to be s, the theory of the composition of acids and salts was almost complete. Analogy indicated that the alkalis and the earths must be oxides of metals. If experimental investigation should confirm this supposition, the edifice was finished."

"Alkali (Arabic = the ash). This term was originally applied to the ashes of sea-plants; but it was soon extended to include substances which, like the ash of sea-weed, easily dissolved in water, forming solutions which had a soap-like action on the skin, affected the colour of plants, and reacted with acids with effervescence and the production of new substances wherein neither the properties of the acids nor those the alkalis were prominent."

"Van Helmont and his successors recognised two kinds of alkali, fixed and volatile; Duhamel, in 1736, divided fixed alkali into two classes, vegetable (), and mineral alkali (soda)."

"[A]t about the time of the discovery of oxygen, salts were thought of as compounds formed by the addition of s to bases which were generally alkalis or earths; if a mild alkali or a mild earth was the basis, fixed air escaped; if a caustic alkali or earth was the basis, fixed air was not produced."

"Little or nothing was known regarding the composition of alkali until the year 1755 when Black (on the occasion graduating as MD at Edinburgh) published dissertation on 'Magnesia Alba, Quicklime, other Alkaline Substances.' Magnesia alba dissolved in s with effervescence; but after being strongly heated no effervescence attended the solution of this alkali."

"In the time of Stahl the name "salt" was applied... to the substance produced by the union of an acid with an alkali; but the same word was used by the alchemists with an altogether different signification."

"The chemical histories of the three classes of compounds s, s, and bases, are closely interwoven. Black's quantitative experiments led to the division of alkalis and earths into two classes; mild alkalis and mild earths, and caustic alkalis and caustic earths or quicklimes."

"The alkalis are classed with the s, i.e. compounds of hydrogen and oxygen with a third element, rather than with the hydrates, i.e. compounds of water with an oxide or a salt. (v. Hydrates)."