Chemical Nomenclature, the vocabulary of terms used in chemistry. Being the instrument of thought upon chemical subjects, it lias necessarily at every period in the history of the science reflected the general intellectual character of the time, as well as the stage of development which chemistry had attained. The crude notion of ancient writers that the heavenly bodies exercised an influence upon terrestrial affairs is expressed in the language of the period by such names as Sol for gold, Luna for silver, -Jupiter for tin, Mars for iron, Venus for copper, Saturn for lead; and the progress of the study was greatly retarded by the confused terms then employed. In truth, few events are recorded in the history of chemical science which have exerted a more beneficial influence upon its progress than the adoption of the admirable method of nomenclature brought forward by Guyton de Morveau in 1782, modified by a committee of the French academy, of which Lavoisier was chairman, in 1787, and published under their auspices in a volume entitled Methode de nomenclature chimique (Paris, 1787). Several chemists had previously perceived the importance of designating compound bodies by the names of their components, and had endeavored to improve upon the indefinite and irrational names adopted by the alchemists; but no satisfactory general system had till then been devised.
It should be mentioned at starting that the system of nomenclature here to be described is so intimately connected with certain theoretical views of the constitution of compound bodies, that any treatise upon it must become also in a measure a description of the methods of classification upon which it depends. The main feature of the system consists in forming in a simple and uniform manner the name of any and every compound from the names of the substances of which it is composed. The elements alone are subject to no rule, their names depending entirely upon the choice of the discoverer. It is true that the framers of the nomenclature sought in several instances to express some one prominent property of the element by means of its name, as in the case of oxygen (Gr. ofuc, acid, and yewaeiv, to generate), which was thought to be "a principle necessary to acidity," and hydrogen (Gr. vdup, water, and yewaeiv). But these attempts were confined to the elements which at that time had been recently discovered; the common names of all the well known metals, alkalies, etc, having been retained. Of the elements which have since been discovered, some have been named in allusion to striking peculiarities, as chlorine (x?Mp6c, green), iodine (, violet), etc.
For the most part, however, names devoid of any chemical significance have been chosen, the propriety of which course is now very generally admitted by chemists. In choosing the name of an element, it is important only that it shall be well adapted to the formation of compound names. In accordance with Davy's suggestion, the names of the more recently discovered metals have received a common termination um, as potassium, platinum, etc. The idea of applying some one uniform termination to each of the members of a natural group had previously been suggested by Bergman, from whom it was adopted also by the French nomenclaturists, who proposed that the names of metals should all terminate in e, as platine, cuivre, etc. The names of another class of elements terminate in ine, as chlorine, iodine, etc. - The elements are divided into two classes, metals and non-metallic bodies (metalloids). The metals all possess certain analogous characteristic properties. The class of metalloids, however, includes several quite distinct groups of elements. - When two elements of unlike properties combine with each other, the product is termed a binary compound. Binary compounds are divided into three great classes, acids, bases, and indifferent bodies. The last have but little chemical activity.
Acids and bases, however, possess unlike properties, and, although they do not combine with the elements, still manifest a great disposition to unite one with the other. Ternary compounds, or salts, are thus formed. The resulting salt possesses new properties unlike those of its components, having usually but little affinity for other substances; but some salts can unite with others to form quaternary bodies (double salts). The distinctive properties of these several classes are by no means absolute. Indeed, there are many bodies which, according to circumstances, act either as acids or as bases: as acids when brought in contact with strong bases, and as bases toward strong acids. Those acids which are soluble in water are distinguished by their power of changing the blue color of a solution of litmus to red. Bases, on the contrary, reproduce the blue color of litmus which has been reddened by an acid. The most characteristic salts have but little or no action on red or blue litmus, the acid and basic qualities of their components having been entirely neutralized by combination. There are, however, many exceptions to this, as will be seen further on.
When a solution of a salt is subjected to a weak galvanic current, the acid and base of which it consists are separated from each other; the acid collects at the positive pole of the battery, the base at the negative pole. On the theory that like electricities repel, while unlike attract each other, it is evident that the particles of matter which are attracted to the positive pole ought to possess negative electricity, while those attracted to the negative pole should be positively electrified. The base is therefore often called the electro-positive and the acid the electro-negative constituent of the salt. The character of the respective constituents of a salt may hence be exhibited by submitting the latter to the action of galvanism. The same rule applies also to all binary compounds which can be electrolyzed. - In view of the great prominence which oxygen had attained in consequence of the experiments of Lavoisier, and of the fact that most of the acids and bases known to the founders of the chemical nomenclature contained it, or were thought to contain it, as one of their constituents, it is not surprising that especial importance was attached to this element. Indeed, its compounds form the basis of the system.
The binary compounds of oxygen are, with the exception of a few indifferent substances, either bases or acids. They are called oxides, the termination ide, which is indicative of combination, being added to the first syllable of oxygen. Although the term oxide is generic, and would, strictly speaking, apply with equal force to any compound of oxygen with an element, it is nevertheless usually restricted to those compounds which are destitute of acid properties, viz., to the bases and indifferent bodies. Its acids are often called oxy-acids. The name of any particular oxide is formed by adding the name of its other element to this generic term; thus, the base formed by the union of oxygen and lead is called oxide of lead, that containing oxygen and potassium, oxide of potassium, etc. Lead and potassium are in these instances electro-positive elements, oxygen being electronegative in regard to them. As a general rule, the name of the electro-negative constituent of a compound determines its genus, while that of the electro-positive constituent defines the species. The names of the basic compounds which oxygen forms with metals whose names end in um are often made to terminate in a; thus, instead of oxide of sodium and oxide of barium, the terms soda and baryta are used.
Oxide of calcium furnishes the most striking exception to this rule, the common name lime being used instead of calcia. Oxygen usually combines with an element in more than one proportion, forming several bases. To distinguish these, the prefix proto (Gr., first) is applied to the oxide in which one equivalent of oxygen is united with one equivalent of the element. An oxide containing less than one equivalent of oxygen to one of the other element is called a sub-oxide (Lat., under). The prefix sesqui (one and a half) denotes a compound in which the oxygen is to the other element in the ratio of 3 to 2; dcuto (Gr., second) or tin (Lat. bini, two), an oxide containing two equivalents of oxygen; and trito (, third) or ter (terni, three), an oxide containing three equivalents of oxygen to one of the other element. The base containing the largest amount of oxygen is often called the peroxide (per, thorough). Thus, three compounds of the metal manganese and oxygen are distinguished as follows:
Protoxide of manganese contains
1 eq. of manganese,
1 eq. of oxygen.
Sesquioxide of " "
2 eqs. of manganese,
3 eqs. of oxygen.
oxide of "
1 eq. of manganese,
2 eqs. of oxygen.
At the time when the nomenclature was framed, it was believed that only two acid compounds could be formed by the combination of oxygen with another element. These were distinguished from each other by causing the name of the other element to terminate in ic for the combination containing the larger proportion of oxygen, and in ous for the compound containing less oxygen, the word acid being added in each case to the words thus formed. For example, two compounds of sulphur and oxygen are respectively:
Sulphurous acid, composed of
1 eq. of sulphur,
2 eqs. of oxygen.
Sulphuric acid, " "
1 eq. of sulphur.
3 eqs. of oxygen.
Of the compounds which an element may form with oxygen, those containing the larger number of equivalents of the latter are usually acids: those containing but few equivalents of oxygen are bases; while not unfrequently the intermediate degrees of oxidation are indifferent bodies, thus, of the oxides of manganese just referred to, the proto- and sesqui-oxides are bases, and the bin- (or per-) oxide is an indifferent body; there are also two compounds containing more oxygen which are acids, viz.:
Manganic acid, containing
1 eq. of manganese,
3 eqs. of oxygen.
Permanganic acid. "
2 eqs. of manganese,
7 eqs. of oxygen.
The compounds which oxygen forms with the metals are, however, for the most part bases, those with the metalloids acids. - Many of the binary compounds of sulphur are analogous to those of oxygen. They are termed sulphides, and as a rule correspond with the oxides. Like the latter, they may be classed as acids, bases, and indifferent bodies. Members of the first two classes, like the oxyacids and bases, unite with each other to form sulpho-salts. They have, however, comparatively little affinity for the other elements, or for compounds not containing sulphur. The sulphur bases and the indifferent sulphides are distinguished by the same prefixes as the oxides. Thus, the three sulphides of iron are termed respectively: protosulphide of iron, symbol FeS; sesqui-sulphide of iron, Fe2S3; and persulphide of iron, FeS2. The sulphur acids are named by prefixing the term sulpho to the name of the corresponding oxygen acid; thus, the compound of carbon and sulphur analogous to carbonic acid is called sulpho-carbonic acid. The binary compounds of chlorine and of several other elements are named in a similar manner.
Thus, with the other elements, oxygen forms oxides; sulphur, sulphides (sulphurets); chlorine, chlorides; bromine, bromides; iodine, iodides; fluorine, fluorides; phosphorus, phosphides (phosphurets); carbon, carbides (carburets); nitrogen, nitrides, etc. When several chlorides, bromides, iodides, or fluorides of any one metal occur, they are distinguished by the same prefixes as the oxides. The binary compounds of these elements are, however, usually regarded, not as acids and bases, but, like the ternary oxygen compounds, as salts. This exception is one of the fruits of the too hasty assumption by the founders of the nomenclature, that oxygen was the universal acidifying principle; an error which lies at the basis of their system, and constitutes one of its greatest faults. It has since been ascertained that the metalloids in question, as well as some others, by uniting with hydrogen, form acids as energetic and as well characterized in every respect as the oxy-acids; for example, chloride of hv-drogen, fluoride of hydrogen, etc. These are called hydracids. Instead of being written out in full, as they have just been given, the names of these compounds are formed by fusing together those of their constituents, as chlorhy-dric acid, fluorhydric acid, etc.
The synonymous names, as hydrochloric and hdyrofiuoric acids, are still often used, but are not in accordance with the general principle that the name of a compound must commence with that of its electro-negative component; their inaccuracy was pointed out simultaneously by Thenard and Dr. Hare of Philadelphia. The hydracids are capable of uniting directly with basic oxides or with metals, with separation of hydrogen in either case; in the first instance the hydrogen unites with the oxygen of the metallic oxide to form water, in the latter it is evolved as gas. The compounds thus formed were at first thought to contain oxygen, the hydracids being supposed to be oxvirenated, and were admitted as salts without question; indeed, one of them, common sea salt, is that from which the very idea of a salt was originally derived. An attempt has since been made to refer them to the oxygen class by supposing that they constitute when in solution, not simple binaries, but compounds of the original undivided hydracid with an oxide.
Thus the compound of chlorine and sodium (common salt) was at one time often called chlorhydrate (or hydrochlorate) of soda; it being claimed that the elements of an equivalent of water had united with its constituents to form chlorhydric acid and oxide of sodium (soda). From this (conventionally admitted) property of chlorine, and the metalloids allied to it, to form salts by direct combination with metals, they have been termed halogens (salt producers; Gr. alg, [sea] salt, and yewaeiv), and their salts have been called haloid (from dig and, in the likeness of) to distinguish them from the oxygen salts. - The names of ternary compounds or salts, in the original acceptation of the term, are formed by combining the names of the acid and base of which they are composed, the name of the acid or electronegative component supplying the generic, the base or electro-positive compound the specific name. If the name of the acid terminates in ic, this termination is changed into ate; if in ous, into ite; and to the words thus formed the name of the base is added. For example, sulphuric acid and oxide of lead form sulphate of the oxide of lead; sulphurous acid forms a sulphite of the same oxide; while hyposulpnu-rous acid produces a hyposulphite, and hypo-sulphuric acid a hyposulphate.
In like manner the compounds of nitric acid are nitrates, and those of nitrous acid nitrites of the bases with which they may be combined. When a salt contains as its base the oxide of a metal which forms but one well defined base with oxygen, its name is usually shortened by leaving out the words "of the oxide," which are always understood. Thus, it is customary to say sulphate of lead, instead of sulphate of the oxide of lead; nitrate of potassa, instead of nitrate of the oxide of potassium. In case more than one basic oxide of the same element is capable of combining with acids, the distinguishing prefix of each is retained in the name of its salts; as sulphate of protoxide of iron, and sulphate of sesquioxide of iron. These salts are also often called respectively protosulphate and persulphate of iron, the prefixes being understood to refer to the degrees of oxidation of the metal. As the number of salifiable oxides of any element is rarely if ever greater than two, it was proposed by Berzelius to distinguish them in some cases, like the acids, by the terminations ous and ic. The two oxides of iron he called ferrous oxide and ferric oxide respectively, and the salts just mentioned ferrous and ferric sulphate; and so with the oxides of various other metals.
These changes are very convenient in certain cases, and for these they have been extensively adopted. - It often happens that an acid can combine with the same base in several different proportions. Of the salts thus formed, one is called neutral, or more properly normal, since the definition now depends upon some one constant relation in which the oxygen of the acid stands to that of the base for the salts of each individual acid; those containing more base than this are termed basic, and those containing less, acid salts. The term neutral or normal is not usually expressed, being understood to belong to any salt which is characterized neither as basic nor as acid. When several acid salts of any one base occur, they are distinguished from each other by the Latin prefixes hi, ter, etc, which are attached to the name of the acid; thus, monochromate (or simply chromate), bichromate, and terchromate of potassa. When several basic or sub-salts occur, they are usually distinguished by prefixing the terms bibasic, sesquibasic, terbasic, etc, to the name of the salt.
Thus, five acetates of lead are known: monobasic (or normal) acetate of lead, symbol PbO a; bibasic do., (PbO)2A~; sesquibasic do., (PbO)3 a.; terbasic do., (PbO)3 a; sexbasic do., (PbO)6 A. It has also been proposed to denote the amount of base in a sub-salt by prefixing to its name the Greek numerals dis (twice), tris (thrice), tetrakis (four times), etc, in contradistinction to the Latin ones used for acid salts. Thus, instead of bibasic acetate of lead, the term diacetate of lead would be used; instead of terbasic acetate of lead, trisacetate of lead, and so on. Many oxides act as bases under certain circumstances, and as acids under others; they may have therefore two different names. Thus, the oxide of aluminum when acting as a base is called sesquioxide of aluminum (or alumina); but when playing the part of an acid, it is termed aluminic acid. Water (protoxide of hydrogen) is another oxide which is either acid or basic according to circumstances; when it plays the part of an acid its salts are termed hydrates, as hydrate of potassa, etc. The principles of the nomenclature have not been carried out, however, in regard to the compounds in which it acts as a base.
Several of our most common acids are such compounds; but instead of saying sulphate of water, nitrate of water, etc., they are termed hydrated sulphuric acid, hy-drated nitric acid, etc.; or, oftener, simply sulphuric or nitric acid, terms which ought, strictly speaking, to be applied only to the anhydrous compounds. In like manner certain salts, which contain two equivalents of acid united with one equivalent of a metallic base and one equivalent of water, which ought to be regarded as double salts, are named as if they were bisalts, containing two equivalents of acid to only one of base, the water being left out of account. Thus the compound of one equivalent of water, one equivalent of potassa, and two equivalents of sulphuric acid, is commonly called bisulphate of potassa. - The names of some of the ternary sulphur compounds (sulphur salts) are formed in a similar manner to those of the corresponding compounds of oxygen; thus the compound of sulphide of sodium and sulphantimonic acid is called sulphantimoniate of the sulphide of sodium. Like the names of the oxygen salts, these are usually abbreviated. In the instance cited, the salt is commonly termed sulphantimoniate of sodium, it being understood that the latter element is united with sulphur.
But this system is limited to only a few of the sulphur acids; the terms sulpharseniate, sulphantiinoniate, and sulphomolybdate are well understood; but the sulphophosphates, for example, of Berzelius (MS, PS5) have never been generally so called. - So long as the attention of chemists was principally directed to the consideration of inorganic compounds, the system of nomenclature just described, in spite of its numerous faults and inconsistencies, was found to be sufficiently expansive to meet all requirements. It has, however, failed to furnish suitable names for many new classes of compounds which have recently been discovered. This is especially true of the great variety of organic substances, with the study of which chemists of the present day are chiefly occupied. But the radical fault of the system is its intimate connection with the so-called du-alistic theory as just developed, which supposes all compounds to be capable of division into two prime factors, as salts into acids and bases, and these into still simpler antagonistic components; a view which is at present generally discarded. The system of nomenclature in question has moreover been found to be incapable of expressing innumerable decompositions and changes which occur among complex substances.
But this difficulty has been in a measure obviated by the introduction of certain written abbreviations (see Symbols, Chemical) and formulas, which exhibit at once to the eye the composition of bodies and the alterations to which they are subject. Indeed, since the adoption of these symbols the name of a substance is of comparatively little scientific importance. The introduction of many names synonymous with those now used has thus been unquestionably prevented, and numerous other alterations obviated. There is a numerous class of compounds termed compound radicles which, though they contain several elements, nevertheless comport themselves like simple substances toward the elements. For example, cyanogen, a compound of two equivalents of carbon and one equivalent of nitrogen, exhibits properties closely analogous to those of the element chlorine. In general the term radicle is applied to any substance which by uniting with an element can give rise to an acid or a base. Many of the more simple compounds formed by the union of compound radicles with elements or with other compound radicles are classed with the chlorine salts; as cyanide of potassium, chloride of ethyl, etc, the radicle ethyl being composed of four equivalents of carbon and five of hydrogen.
Some of the compound radicles acting as metals can unite with oxygen to form bases or acids, which, when combined with each other, produce salts which are completely analogous to the oxygen salts of inorganic chemistry. Thus the radicles ethyl and benzoyl, after combination with oxygen, are respectively a base and an acid, which by uniting form benzoate of the oxide of ethyl (benzoate of ethyl). In general terms it may be said that the nomenclature of organic acids, bases, and salts is similar to that of analogous inorganic substances. It is among the radicles themselves, and the numerous neutral or indifferent complex bodies of organic chemistry, that the system is at fault. Organic compounds are usually divided into natural families or groups, the generic names of which are furnished in each case by the name of some one substance which happens to be familiarly known, and to which each member of the group is in some way allied. Thus the term alcohol is applied to a large class of bodies analogous to common alcohol, each separate member of the class being designated by prefixing its specific name; as methyl alcohol (wood spirit), ethyl alcohol (common alcohol), etc. In like manner ether is the generic name of a large class of bodies of which common ether is the type.
In compounds produced by substitution (see Chemistry), that is, in those cases where one or more of the equivalents of an element are replaced in a compound by equivalents of other elements or of compound radicles, names are formed by prefixing to the name of the original compound that of the element or elements which have been newly introduced. The prefixes bi, ter, etc or di, tris, tetra, etc, if the replacing substances possess basic properties, are used to denote those cases where two or more equivalents of any one element are substituted. Thus, acetic acid in which one equivalent of hydrogen has been replaced by an equivalent of chlorine is called chlor-acetic acid (or monochloracetic acid); when three equivalents of hydrogen are thus replaced, it is called terchloracetic acid. When one equivalent of hydrogen in ammonia is replaced by ethyl, the resulting compound is called ethyl-ammonia, or shortly, ethylamine; when two equivalents of hydrogen are thus replaced, it becomes diethyl-ammonia (diethyl-amine), and so on.
But each of the three equivalents of hydrogen in ammonia may be replaced by separate radicles, as in ethyl-methyl-amyl-ammonia. In similar cases exceedingly complicated names are often unavoidable; but such are rarely expressed without their written formulas. - Two or three common prefixes, besides those already mentioned, occur. Thus, pyro (abbreviated by Guyton de Morveau from the term empyreu-matic, much used by the alchemists) is a distinguishing appellation of many acids obtained by means of dry distillation, as pyrogallic acid, etc. Para (Gr., near to) was proposed by Berzelius to indicate a strong resemblance between two compounds, as tartaric and para-tartaric acids, which, though very much alike, must nevertheless be regarded as distinct substances. Meta (Gr., signifying change) is also used in a somewhat similar manner. Thus, when aldehyde is kept for a long time in a close tube, it gradually changes into two compounds, both isomeric with the original substance; one of these is called metaldehyde, and the other paraldehyde. - Many chemists have sought to apply names terminating alike to all the members of a given class.
Although it is not easy to carry out this principle in detail, it has nevertheless been successfully applied to the names of several classes of compound radicles which terminate in yle, or simply yl, as ethyl, methyl, etc. The names of the alkaloids also, and in general of bases which are not radicles like ethyl, terminate in ine, as strychnine, morphine, and the like. - In the above sketch we have given the nomenclature employed during the last 75 years in the best treatises on technology, and analytical, physiological, pharmaceutical, and general chemistry. But as language is the instrument used to express the existing knowledge on any subject, and as the domain of science has been immensely increased and the theoretical views entertained by chemists have been materially modified, a new nomenclature has been found necessary. It would be impossible to notice in this place the various systems of nomenclature devised as substitutes for the language invented by Lavoisier. One of them, proposed by Prof. Samuel D. Tillman of New York, displayed great ingenuity and a rare adaptation to the progress of chemical science; but as it has not been generally adopted, an analysis of it would be out of place. A greater change has taken place in the notation than in the nomenclature of modern chemistry.
Many of the atomic weights have been doubled; graphic formulas for the expression of the molecular constitution and of the doctrine of substitution in organic chemistry have been found necessary; and the student of the present day is compelled to learn two sets of figures, the dualistic of Berzelius and the unitary of modern times. The departures from traditional English usage in the names of compounds are made to correspond with the changes in notation, and are chiefly verbal. A few illustrations will suffice to make this point clear:
Carbonate of potash.
Bicarbonate of potash.
Hydrogen potassium carb'ate.
Sulphate of zinc.
Protosulphate of iron.
Persulphate of iron.
Anhydrous sulphuric acid.
In the case of the complicated bodies belonging to organic chemistry, the assumption of compound radicles and other peculiar views of rational constitution have led chemistry to construct various new names, which are to be learned in the writings where they are propounded. Atomicity is a term much employed by modern chemists to denote the equivalent value or combining capacity of an element. It is measured by the number of atoms of hydrogen or other monatomic or univalent element with which the element in question can combine. When an element does not unite with hydrogen, as in the case of many of the metals, its atomicity may be measured by the number of atoms of chlorine, bromine, or iodine with which it can combine, since the atomicity of the elements is equal to that of hydrogen. The atomicity or combining capacity is in most cases a variable quality; and chemists have found it convenient to divide the elements into two classes, one of odd, the other of even equivalence. Those of odd equivalence are called perissads, those of even equivalence artiach; e. g.: perissads - nitrogen, phosphorus, arsenic, antimony, gold; artiads - oxygen, sulphur, selenium, tellurium, barium, calcium, magnesium, tin, etc.
The fact that the older nomenclature has been so long in use among chemists, pharmacists, phy-. sicians, and manufacturers, and that so vast a mass of literature has been written in accordance with it, has made scientific men very reluctant to abandon it. But the new facts and theories continually brought forward as the science advances require a change in classification and language; and the greater truth of modern chemistry must ultimately compel the adoption of the new notation and nomenclature.