Chemical Society
AMERICAN, a society founded in 1876 for the discussion and consideration of subjects relating to chemistry. It holds annual meetings. It has a membership of about 7,000. It publishes the "Journal of the American Chemical Society," and the forms a substance ter and the changes which it undergoes through the action of various agencies.
In considering this definition, however , it is necessary to distinguish between physical changes and chemical changes.
Thus, when water is frozen, it becomes a solid, and the change from the liquid state is a physical one. No alteration has been brought about in the essential nature of the water, as can be shown by melting the ice, when it again becomes water. When, however, a piece of paper is burned, it is changed into ash and a gaseous mixture, and the change which it undergoes is permanent, its essential nature being altered. In this case, the change is a chemical one, although, like all chemical changes, it is accompanied by physical changes.
It is not always easy to distinguish between physics and chemistry, as the two sciences come very near to one another, but it can be said that chemistry is concerned with those phenomena which involve a change in the molecular structure of a substance. The science is divided into two great branches-Inorganic and Organic. The former includes the study of all substances of a mixed character. The latter formerly concerned itself with substances of animal or vegetable origin, but this classification is no longer recognized, and it may now be said to cover the chemistry of the compounds of carbons, excluding such obviously inorganic substances as mineral carbonates and some similar compounds.
Particular departments of Chemistry, where the science is confined to the examination of special objects, receive distinctive names, as Physical Chemistry, or Chemical Physics, which considers phenomena bordering on Physics and Chemistry; Mineralogical Chemistry, which takes cognizance of the composition of minerals; Physiological Chemistry, which includes the changes which food undergoes in its transit through the animal economy, and the transformations that take place in substances of organized beings generally; Agricultural Chemistry, which relates to the composition of soils and manures, the ingredients in plants, and the best modes of supplying the food that they require, etc. Two classes of chemical work may be accepted as typical of the science. One is analysis, signify-. ing unbinding; and the other is synthesis, or putting together. By the first process the chemist ascertains the composition of a substance; by the second process he forms a substance by bringing together 29-Vol. II-Cyc CHEMISTRY and combining the constituents. Analysis has been applied to almost all substances that exist on the earth, as well as to meteorites, and it has been found that they are all composed of about 80 constituents which are called elements. But of these only 12 enter largely into the composition of the earth. prosecution History. The Egyptians, of all nations of antiquity, appear to have had the greatest amount of chemical knowledge. They skillfully preserved dead bodies from decay, fixed colors in silk by means of mordants, prepared many medicines and pigments, as also soap, beer, vinegar, metals and metallic alloys, common salt, vitriol, soda, sal ammoniac, glass, enamel, tiles, and painted earthenware. The Chinese were very early acquainted with the processes for dyeing and the preparation of metallic alloys, the fabrication of niter, sulphur, gunpowder, borax, alum, porcelain, verdigris, paper, etc. From the Egyptians the Greeks and Romans derived what chemical knowledge they possessed, but they added little or nothing; and at the migration of the northern tribes, and the overthrow of the Roman Empire, a stop was put for a time to the advancement of all science in Europe. The prosecution of chemical knowledge was taken taken up by the Arabs before the 8th century, and was carried on by them and by their European scholars, calling themselves alchemists. The first germs of the real science of chemistry appear about the end of the 17th and beginning of the 18th century, in the speculations of Becher and Stahl. After this chemistry rapidly advanced. In 1718 Geoffrey brought out the first table of affinities; in 1732 Boerhaave published many original experiments on the chemical relations of heat and light; in 1724 Hales, and in 1756 Black, published researches on the air and aeriform bodies, showing that the carbonic acid evolved during fer mentation, respiration, and by the action of acids on chalk was different from atmospheric air. In 1754-1759 Margraff added to the then known earths-lime and silica-two others, alumina and magnesia; he also extracted sugar from plants. In 1770 Priestley began to announce his discoveries of oxygen, ammoniacal, hydrochloric and sulphurous acid gases, etc. In 1772 Rutherford discovered nitrogen, and in 1773-1786 Scheele contributed chlorine, hydrofluoric, prussic, tartaric, and gallic acids; also baryta, phosphoric acid from bones, etc., and gave the first hints regarding a new doctrine of combustion. About the same time Bergman and Cavendish_enlarged our knowledge of the gases. Lavoisier, during fer- CHEMISTRY between 1770 and 1794, reorganized much of the then known chemistry, and founded a system which still remains the frame-work of the science. Berthollet, 1787, contributed much to the doctrine of affinity, and made researches in chlorine, etc. Fourcroy and Vauquelin advanced Organic Chemistry. Klaproth gave many contributions to Mineral Chemistry. Richter devoted himself to the doctrine of combining proportion in the molecule afterward perfected by Dalton. The discovery of ga galvanic electricity by Galvani, and its advancement by Volta, led Sir Humphrey Davy and others to important researches in the metals and gases. Gay-Lussac and Thenard advanced the knowledge of organic substances and the chemical relations of heat. Berzelius made laborious researches in mineral chemistry, and gave an exactness to this department which is an astonishment to the chemists of the present day. He was also the author of the electro-chemical theory, which was almost perfected by the labors of Faraday, De la Rive, Becquerel, etc.
Organic che chemistry advanced most rapidly under the researches of Liebig, Wohler, Mitscherlich, Mulder, Laurent, and, in more recent years, Bunsen, Mendeleef, Ostwald, Van't Hoff, and many others too numerous to mention.
Chemical Nomenclature. - In early times chemical substances were named according to the fanciful theories of Alchemy. Thus the name "flowers of sulphur" was applied to sulphur (sublimed), which grew or sprang like a flower from sulphur when heated; "spirit of salt," to hydrochloric acid, the corrosive acid or spirit obtained from common salt; and a multitude of other names had a fanciful origin. In 1787 Lavoisier founded the system of nomenclature still followed by chemists. At first it was intended that the name of a simple as well as of a compound substance should be regulated by system, and that it should indicate the nature of its elementary constituents, as well as the relative proportion in which they were present. Hence such terms as oxygen, the acid-producer, given from the notion then held that no acid was without oxygen; and hydrogen, the water-producer, from the supposition that hydrogen had more to do with the formation of water than any other element. The advance of chemistry, however, so completely changed the opinion of chemists regarding the simpler bodies that such names were found to mislead; and thereafter, though such as had been given on this system were retained, their meaning was discarded, and the systematized nomenclature restricted to com- CHEMISTRY CHEMISTRY pound substances. In the non-metallic either with three or five atoms of chlorine on. elements a close analogy exists between chlorine, bromine, iodine, fluorine; and to indicate this the common termination ine has been given; and for a similar reason carbon , silicon, and boron end in As a general rule, however, the chemical name of an elementary subname of an elementary substance does not convey any scientific meaning, and must be regarded as a simple mark or designation, analogous to the names of persons , which give no notion regarding their moral character or physical development . The ancient and more common metals retain their popular titles, such as gold, silver, and copper; but the more recently discovered metals have names given which end in um. The symbol of an element is obtained from or first letter of its Latin name , as O for "oxygen"; Pb for "lead" (Lat. plumbum). When the names of two or more elements commence with the same letter a smaller letter or satelor more of these; such as S for "sulphur," Se for "silicon." The most common of these are O., oxygen; H., hydrogen, and N. nitrogen. The name of a compound substance generally indicates the elements of which it is composed.
Thus the name "ferric oxide" indicates that the red powder is made up of oxygen and iron; the name "lead gen and iron; the name "lead sulphide" composed of sulphur and lead. In the first case the adjective is derived from the Latin name of the metal. When two elements combine with each other in more than one proportion or equivalent, the names of the compound bodies are contrived to express this. Thus, oxygen combines with a number of elements to produce with each a series of acid compounds, the more highly oxidized of which receive the terwhile those containing less oxygen end in ous. contains three equivalents of oxygen to Thus sulphuric acid one equivalent of sulphur , and sulphurous acid two equivalents of oxygen with one equivalent of sulphur. "Ferrous chloride" indicates the lower chloride, and "ferric chloride" the higher chloride, of the metal iron. When acids combine with bases or metallic oxides to form salts they produce compounds the names of which are influenced by the terminations of the acids. Thus, sulphuric acid and sodium form sodium sulphate; sulphursodium, sodium sulphite. In the same manner nitric acid combined with potassium forms potassium nitrate, potassium produce potassium nitrite.
Another method, and one which is growing in favor, is the use , phosphorus unites and the compounds are known as phosphorus trichloride and phosphorus pentachloride, respectively. chloride, respectively. Similarly, carbon one atom of oxygen, carbon dioxide, two atoms, and so on.
Chemical Symbols. -A symbol denotes nifies one atom, or 16 parts by weight, of one atom of the element. Thus, 0 sigatom of the element . Thus, O sigoxygen; C, oxygen; C, one atom, or 12 parts by H, one atom, or one part by weight, of hydrogen. numbers of atoms. For instance, a mole- A molecule is composed of various cule of hydrogen contains two atoms, and its symbol is therefore written H2. The molecule of oxygen also consists of two atoms and is written O2. But the ozone molecule contains three atoms of oxygen and is written Os. represented by placing the symbols for The combination of two elements is those elements side by side; thus, H2O of hydrogen and one atom of oxygen in a state of chemical combination (viz ., water), and NaCl is with one atom of chlorine (viz., common one atom of sodium (Lat. natron) united salt). When two or more atoms of one element unite with one or more atoms of another element the number of such atoms is signified by a small figure placed immediately immediately after the symbol of the ele- MnO, is one atom of manganese with two of oxygen (black oxide of manganese), Fe2O3 is two atoms of iron with three atoms of oxygen, and Pb₃O₄ is three atoms of lead with oxygen (red lead). In expressing the formula of a compound substance the symbol stance the symbol of the metal or its generally placed first in order, and is succeeded by the oxygen, chlorine, or similar element. The same order is carried out in the construction of the formula of more complex sub- Thus, ferrous sulphate stances; the metallic half is placed first. sulphuric oxide and the oxide of iron is generally expressed as FeSO4. In containing other words, the symbols are written in the order in which the substances would be named in Latin. pound radicles, consisting of two or more atoms, combined together to act as a single atom within the molecule. Amexample of this.
The formula for ammonia gas is NH3, and in aqueous solution it combines with water to form ammonium hydroxide, radicle (NH.) in many compounds and whereas it is one atom of nitrogen H.) exists and four of hydrogen, it acts as though it were a single atom . For instance. we Some substances contain so-called com- CHEMISTRY saw above, that the formula for ferrous sulphate was FeSO4 The formula for ammonium sulphate is (NH4)2SO4 and, to express the fact that the atoms of nitrogen and hydrogen forming ammonium act as a single entity, parentheses are used, as shown. These symbols and formulæ are valuable and necessary because they enable us to express briefly the exact composition of a substance , and because, by their use, chemical reactions can be shortly expressed in the form of an equation. Thus:
CaCO3 + H2SO4 = CaSO4 + H2O + CO2 indicates that calcium carbonate reacts with sulphuric acid to give calcium sulphate, water and carbon dioxide.
Metals. Largely from their physical characteristics, a number of the elements are called metals. They all possess the metallic luster, are of opposite affinity to oxygen, can within certain limits for each case replace hydrogen in acids and other metals in salts. They conduct electricity and heat comparatively well, and are generally solid at an ordinary temperature. Non-metals. All the other elements are classed as non-metals. Some are solid, such as sulphur and iodine; bromine is liquid, and many are gaseous at ordinary nary ter temperatures, such as oxygen and chlorine. Some elements are on the border line, such as silicon and arsenic, it being hard to class such definitely as metals or non-metals.
Chemical Laws. By many years of patient research the chemists of the late 18th and early 19th century established the fact that all chemical reactions take place in accordance with definite quantitative laws. The first and simplest chemical law is known as the Law of Constant Proportions. This states that: "The same compound always contains the same elements combined together in the same proportion by weight." This law establishes the difference between a chemical compound and a mix ture. A mixture may obviously be compounded of its ingredients in varied proportions. Putty, for instance, may contain more or less whiting, more or less oil, and still it will be putty. But calcium carbonate, which is the chief con- CHEMISTRY Multiple Proportion, which states that: "When one substance unites with another in more than one proportion, these different proportions bear a simple ratio to one another." This law was first established by Dalton. We have already seen that it sometimes happens that the same elements combine to form different compounds. Oxygen will unite with sulphur to give sulphur dioxide, or sulphur trioxide. In the first, 32 parts of sulphur combine with 32 parts of oxygen; in the second 32 parts of sulphur combine with 48 parts of oxygen. The ratio of the different weights of oxygen which will combine with 32 parts of sulphur is, therefore, 32: 48 or 1: 1.5. Similarly, nitrogen will combine with oxygen to give nitrous oxide, nitric oxide and nitrogen trioxide. In the first compound, 14 parts of nitrogen combine with 8 parts of oxygen; in the second, 14 parts of nitrogen with 16 parts of oxygen; in the third, 14 parts of nitrogen with 24 parts of oxygen. Here, the ratio of the different weights of oxygen which combine with a definite weight of nitrogen is 8: 16 : 24 or
1 : 2 : 3. A simple ratio , as illustrated in these two examples, is found in every similar case, thus establishing the second law of chemistry. The third law is called the Law of Reciprocal Proportions, and states "The weights of different elements which combine separately with one and the same weight of another element are either the same as, or simple multiples of, the weights of these different elements which combine with each other." To make this clear, let us take a concrete example.
Hydrogen, oxygen, and chlorine will all combine with sulphur. In the case of hydrogen, two parts combine with 32 of sulphur, in the case of oxygen, 32 parts with 32 parts of sulphur, and in the case of chlorine, 35.5 parts with 32 parts of sulphur. Now let us see what the law of reciprocal proportions would lead us to infer from these figures. The weights of the three elements given above, which combine with the same weight of sulphur, are 2, 32 and 35.5, respectively. If any two of these elements combine with each other, therefore, we should expect the weights which combine to be either the them. Let us take the first two, hydrogen same as the above or simple multiples of stituent of whiting, will always contain calcium, carbon, and oxygen combined in the same proportions. It may be dug from the earth as calcite, or prepared and oxygen. Two parts of hydrogen combine with 16 parts of oxygen, and 16 artificially by treating lime with carcombine with 16 parts of oxygen, and 16 bonic acid, or obtained as a precipitate is exactly one-half of 32. Take hydrogen by treating sodium carbonate solution and chlorine. Two parts of hydrogen with calcium chloride, but, however ob- combine with 71 parts of chlorine, and tained, it will always always contain 40 parts of 71 is exactly twice 35.5. We see, therecalcium to 12 parts of carbon and 48 fore, that the law holds good, and the parts of oxygen. same will be found true no matter what elements are considered.
Another fundamental law is the Law of CHEMISTRY An examination of these three laws led Dalton to formulate the Atomic Theory of Matter, although other chemists before him had put forward from time to time a similar hypothesis. Expressed briefly, the theory is that matter is made up of minute particles called atoms, and that chemical combination takes place between these atoms. Atoms of the same clement are similar to one another and equal in weight, and compounds are formed by the union of atoms of differ ent clements in simple numerical proportion-1:1, 1:2, 2:3, 5: 1, and so on. This theory forms the basis of quantitative chemical work, and modern chemistry offers an overwhelming mass of evidence that the theory is true. The Status of Chemistry. The importance of chemistry in daily life can scarcely be over-estimated. Most of our industries are largely dependent upon it, including the manufacture of iron and steel, paper, glass, photographic materials, oils, drugs, dyes, explosives, soaps , concrete, paint, perfumes, mes, and many others. The manufacture and application of fertilizers forms the connecting link between this science and the farm, and the preparation of foodstuffs, flavorings, and essences brings chemistry into the kitchen. Some knowledge of chemistry, moreover, is a necessity to the physician, the engineer, or the electrician. It is, therefore, clear, that modern existence is more dependent upon chemistry than upon any other science.