Mixture

“ Care should be exercised to distinguish chemical compounds from simple mixtures. Air is not a compound, but a mixture of oxygen, hydrogen and nitrogen gases. Water, however, is a compound of oxygen and hydrogen. Both salt and [30] sugar are compounds, but if we grind them together, we do not have a new compound, but a mixture of two compounds. Most of the common things around us are mixtures of different compounds or substances. Rocks are mixtures of many different compounds. Wood is, likewise, formed of many different substances. ”

“ The mixture is to be thrown into the first mass of ingredients—the living stuff into the gross—at the moment of boiling—that is the secret, which I do not mind communicating to a friend of the science. ”

“ It is evident that no new substance has been formed by rubbing the salt and iron together. The product is called a mechanical mixture. Such mixtures are very common in nature, almost all minerals, sands, and soils being examples of this class of substances. It is at once apparent that there is no law regulating the composition of a mechanical mixture, and no two mixtures are likely to have exactly the same composition. ”

“ Before we quit the consideration of medicinal compounds as the results of chemical action, it is expedient to remind the practitioner of the essential difference between Mixture and Combination, a difference which affects the medicinal virtues no less than the chemical characters of bodies ”

“ It is generally effected by means of heat, which has a tendency to separate the particles of bodies from each other; or by the mixture or combination of some other matter with the matter intended to be examined. The mixture of two or more compounds often produces a decomposition by means of chemical affinity, a property which different species of matter have to unite with each other ”

“ Certain solids also consist of two or more components which are united so as to show' similar effects. All these cases of solution are to be distinguished from chemical compounds on the one hand, and from simple mixtures on the other. When a substance contains its components in definite proportions which can only change, if at all, by sudden steps, it may be classed as a chemical compound. When the relative quantities of the components can vary continuously within certain limits, the substance is either a solution or a mixture. ”

“ Thus we have traced out the distinction between mechanical aggregation and chemical affinity, taking for an example the difference between gunpowder as a whole (in which the ingredients are so nicely balanced that it is almost a chemical combination) , and its constituents, sulphur, charcoal, and nitre, when they are chemically combined; or, in briefer language, we have noticed the difference between the mechanical mixture, and some of the chemical combinations, of three important elements. ”

“ It is very important, too, if the pupil has not already studied chemistry, that he should be led to some comprehension of the nature of chemical union and of the difference between a chemical compound and a mechanical mixture. ”

“ It will still help to make iron rust; and salt will be salty, whether or not it is dissolved in water. That is why [pg 310] solutions are only mixtures and are not chemical compounds.
Everything in the world is made of atoms. Everything in the world is either an element or a compound or a mixture. Most plant and animal matter is made of very complicated compounds, or mixtures of compounds. ”

“ The volume of the mixture equals the sum of the volumes of the things mixed, and there is no change in the properties of these things. So when water evaporates, the gaseous water or vapour mixes with the air in the same way, the molecules of the one body dispersing themselves between 74the molecules of the other until there is the same proportion of each everywhere. ”

“ Everything which aggregates or grows to a definite shape, appears to select its material; if a crystal of a particular salt is placed in a mixture of saturated solutions of different salts, it will only select and assimilate to itself suitable material, either particles of the same composition as itself, or those which are isomorphous with it, i.e. ”

“ To state the matter precisely, however finely two fluids have been 256 subdivided by agitation, the molecular constitution of the different portions remains unchanged. The ultimate process by which the individual molecules of two different substances become mixed, producing finally a homogeneous mixture, is in every case diffusion. ”

“ Matter can neither be created nor destroyed, though it can be changed from one form into another.
Classification of matter. At first sight there appears to be no limit to the varieties of matter of which the world is made. For convenience in study we may classify all these varieties under three heads, namely, mechanical mixtures, chemical compounds, and elements.
Fig. 1
Mechanical mixtures. If equal bulks of common salt and iron filings are thoroughly mixed together, a product is obtained which, judging by its appearance, is a new substance. ”

“ If the relation of aliments to each other follows the analogy of the objects of chemistry, then their union will be influenced by many external circumstances, such as heat and cold, dilution, concentration, rest, motion, and the addition of substances which promote unnatural, or destroy natural mixtures. ”

“ A compound is a substance which is made up of elements united in exact proportions by a force called chemism, or chemical affinity.
A mixture is composed of two or more elements or compounds blended together, but not held by any chemical attraction.
To which of these three classes does sugar belong? Carbon? The solution of sugar in water?
Carbon is an element; we call its smallest particle an atom.
An atom is the smallest particle of an element that can enter into combination. Atoms are indivisible and usually do not exist alone. Both elements and compounds have molecules. ”

“ Those that admit only contact need not detain us. They are dealing with mixture, not with the coalescence which makes the total a thing of like parts, each minutest particle being composed of all the combined elements. ”

“ This constancy both in freezing point and composition formerly was considered as a characteristic of a pure chemical compound', and hence these mixtures were described as components and given the name of “cryohydrates.”
In representing on a diagram the phenomena of equilibrium in a two-component system we require a third axis along which to plot the composition of a variable phase. It is usual to take three axes at right angles to each other to represent pressure, temperature and the composition of the variable phase. ”

“ These conditions being established, and carried to an extent of which, as yet, science has afforded us no evidence, chemical intermixture may have taken place, and a new series of compounds have been formed, which, by again combining, gave rise to another and more complex class of bodies. ”

“ When a solid such as salt or sugar dissolves in contact with water to form a uniform substance from which the components may be regained by evaporation the substance is called a solution. Gases too dissolve in liquids, while mixtures of various liquids show similar properties. ”

“ When two fluids are diffused together without undergoing any change of their chemical properties, they are said simply to be mixed, and not combined; as milk and water when poured together, or as oxygen and azote in the common atmosphere. So when salt or sugar is diffused in water, it is termed solution, and not combination; as no change of their chemical properties succeeds. ”

“ If we are talking about a piece of bread, the answer is, of course, "flour, water, milk, shortening, sugar, salt, and yeast." But what is each of these made of? Flour is made of wheat, and the wheat is made of materials that the plant gets from the earth, water, and air. Then what are the earth, water, and air made of? A chemist is a person who can answer these questions and who can tell what almost everything is made of. And a strange thing that chemists have found out is this: Everything in the world is made out of one or more of about eighty-five simple substances called elements. ”

“ Let us suppose it pounded to a pulp or powder more impalpable than any mince-meat; let us suppose this powder to become fluid, and then to be so stirred and mingled that all its particles, even down to a degree of tenuity far beyond what can be conceived, shall be mixed through and through each other; if we suppose this, it is obvious that we should obtain a mass of matter, each portion of which, however minute, would contain samples of all the ingredients which entered into the composition of the whole. ”

“ Of which is the sugar experiment an example? Metathesis is an exchange of atoms in two different compounds; it gives rise to still other compounds.
A chemical change may add something to a substance, or subtract something from it, or it may both subtract and add, making a new substance with entirely different properties. Sulphur and carbon are two stable solids. The chemical union of the two forms a volatile liquid. A substance may be at one time a solid, at another a liquid, at another a gas, and yet not undergo any chemical change, because in each case the chemical composition is identical. ”

“ The chemical combination of two substances produces, as is well known, a third substance, with properties different from those of either of the two substances separately, or of both of them taken together. Not a trace of the properties of hydrogen or of oxygen is observable in those of their compound, water. The taste of sugar of lead is not the sum of the tastes of its component elements, acetic acid and lead or its oxide ”

“ Nature’s Chemistry—Changes produced by Chemical Combination—Atomic Constitution of Bodies—Laws of Combination—Combining Equivalents—Elective Affinity—Chemical Decomposition—Compound Character of Chemical Phenomena—Catalysis or action of Presence—Transformation of Organic Bodies—Organic Chemistry—Constancy of Combining Proportions—The Law of Volumes, the Law of Substitutions, Isomeric States, &c.
All things on the earth are the result of chemical combination. The operations by which the commingling of molecules and the interchange of atoms take place, we can imitate in our laboratories ”

“ The student will thus be brought to the chemical conception of the molecule as the smallest mass of any substance in which the qualities inhere, and he will come to regard a chemical process as always taking place between molecules.
Thus far nothing has been said about the composition of matter. A chemical process has been defined simply as certain factors yielding certain products, but nothing has been determined about the relations of these several substances except in so far as they are defined by the three laws illustrated above. ”

“ If the change is a combination, or coalescence, of two things into one, then the mass, and hence the weight, of the product is equal to the sum of those masses, and hence those weights, of the things which have united to form it; if the change is a separation of one distinct substance into several substances, then the sum of the masses, and hence the weights, of the products is equal to that mass, and hence that weight, of the substance which has been separated. ”

“ A solution is said to be saturated when it remains unchanged in concentration in contact with some of the solid. The weight of the solid which will completely saturate a definite volume of a liquid at a given temperature is called the solubility of the substance at that temperature. ”

“ That compounding and re-compounding through which we pass from the simplest inorganic substances to the most complex organic substances, has several concomitants. Each successive stage of composition presents us with molecules that are severally larger or more integrated, that are severally more heterogeneous, that are severally more unstable, and that are more numerous in their kinds (First Principles, § 151) . ”

“ If the compound he desires to produce is found to be composed of elements different from those which form the compound wherewith his operations begin, he is directed to bring about a reaction, or a series of reactions, between the compound which is to be changed, and some other collocation of elements the composition of which is known to be such that it can supply the new elements which are needed for the production of the new compound. ”

“ Compare CO and CO2. (3) In the arrangement of atoms, i.e. the molecular structure. Ethyl alcohol and methyl ether have the same number of the same elements, C2H6O, but their molecular structure is not the same, and hence their properties differ.
Qualitative analysis shows what elements enter into a compound; quantitative analysis shows the proportion of these elements; structural analysis exhibits molecular structure, and is the branch to which organic chemists are now giving particular attention. `
A specialist often works for years to synthesize a series of compounds in the laboratory. ”

“ The deposit of a crystal from a solution is a differentiation of the previously mixed molecules; and an integration of one class of molecules into a solid body, and the other class into a liquid solvent. Is not the growth of an organism an essentially similar process? Around a plant there exist certain elements like the elements which form its substance; and its increase of size is effected by continually integrating these surrounding like elements with itself. ”