ration is attained; a saturated combination or solution has been formed. 1 part of linseed-oil may be dissolved in 40, 1000 parts or any greater quantity of alcohol; but when 30 parts of alcohol have taken up 1 part of linseed-oil, any greater quantity remains undissolved and forms a milky liquid on agitation. 10 parts of common salt mixed with any quantity of water greater than 27 pts. will form a clear solution; but if common salt be added by small portions at a time to 27 parts of water, the first 10 pts. will dissolve completely, but any further quantity will remain undissolved. Similar relations are exhibited by water, alcohol and ether towards many salts and other solid bodies, and likewise towards gases. Water and ether agitated together in equal quantities separate when left at rest into two layers; the lower consists of water saturated with ether, which may be replaced by any quantity of water whatever; the upper is ether holding a very small quantity of water in solution, and miscible with ether in all proportions. In most of these cases the point of saturation varies with the temperature and external pressure. Most solid bodies dissolve more abundantly in fluids the more the temperature is raised, probably on account of diminished cohesion; but as exceptions to this law we find that lime and some of its salts dissolve more abundantly in cold than in warm water, and 10 pts. of common salt saturate 27 of water at all temperatures. Under increased pressure, liquids will dissolve larger quantities of gaseous bodies; moreover Perkins found (Ann. Ch. Phys. 23, 410, also Schw. 39, 361) that a milky mixture of alcohol with a larger quantity of bergamot. oil than it can dissolve at the ordinary pressure of the air, became perfectly limpid from solution of the oil under a pressure of 1100 atmospheres. c. Two bodies combine in one or a small number only of definite proportions, subject to no variation from temperature or outward pressure. This law, the most important of all, holds good in all cases in which the more powerful affinities are concerned. It implies a mutual saturation of A with B, and B with A. a. The two bodies A and B combine in one proportion only. In this case the same relative quantities ensure the saturation of A with B, an of B with A. Chlorine and hydrogen combine only in the proportion by weight 35 4:1; zinc and sulphur only as 32.2:16. B. The two bodies combine in 2 definite proportions only: A is satu rated with B at one of these proportions, and B with A at the other. Six parts of carbon combine with 8 pts. of oxygen to form carboni oxide, with 16 to form carbonic acid; in carbonic oxide the oxygen saturated with carbon, in carbonic acid, the carbon is saturated wit oxygen; for 8 oxygen will not take up more than 6 carbon, nor 6 carbon more than 16 oxygen; moreover between carbonic oxide and carboni acid there exists no intermediate combination containing more than 8 and less than 16 of oxygen united with 6 of carbon. It is true that carbonic oxide and carbonic acid gases may be mixed in any proportion whatever and thus a gas obtained in which 6 parts of carbon are present in connection with more than 8 and less than 16 of oxygen: but this is no chemica compound, but a mere mixture of gases, from which potash will remov the carbonic acid and leave the carbonic oxide behind. Similarly 35 4 chlorine with 1014 mercury form corrosive sublimate, and with 202.8 mercury they form calomel: a substance, which for every 35.4 pts. of chlorine contained more than 101.4 and less than 202-8 mercury, would be a mixture of corrosive sublimate and calomel, from which alcohol would dissolve the former and leave the latter. 7. The two bodies combine in 3, 4, or 5 distinct proportions.-In this case the combination of A with the largest quantity of B, gives one point. of saturation, and that of B with the largest quantity of A, the other; between these two points of saturation are situated 1, 2, or 3 intermediate combinations. But here, as in the former case, there is no gradual transition from the minimum to the maximum, but a sudden passage from one characteristic combination to another. 48 molybdenum with 8 oxygen form molybdous oxide, with 16 oxygen, molybdic oxide, and with 24 ox. molybdic acid. 16 sulphur with 8 oxygen form hyposulphurous acid; with 16 ox. sulphurous acid with 20 ox. hyposulphuric acid; and with 24 ox. sulphuric acid. 14 nitrogen with 8 oxygen form nitrous oxide; with 16, nitric oxide; with 24, nitrous acid; with 32, peroxide of nitrogen or hyponitric acid; and with 40 of oxygen, nitric acid. Many intermediate compounds may be regarded as combinations of two saturated compounds in definite proportions. Thus, 103-8 lead form with 8 oxygen (the smallest possible quantity) the yellow, with 16 oxygen (the greatest) the brown oxide of lead: between these is found the red oxide, which contains 103.8 lead with 103 oxygen, or (multiplying by 3) 311-4 lead with 32 oxygen, and may be regarded as a compound of yellow oxide, 2 (103-8 lead + 8 oxygen) and brown oxide (1038 lead + 16 oxygen). Moreover, the red oxide is decomposed by acetic acid, which dissolves out the yellow oxide, leaving the brown. Similarly, magnetic iron ore may be regarded as a compound of protoxide and peroxide of iron. These more intimate and definitely proportioned compounds considered under c, are subject to the two following important laws. FIRST LAW RELATING TO THE SAME TWO BODIES. Suppose two bodies A and B to be capable of uniting in several proportions; then if the smallest quantity of B which can combine with a given quantity of A, be multiplied either by 14, or by 14, or by 2, or by 2, or by 3, 4, 5, or any her whole number, the products will give the other quantities of B, ich may combine with the before mentioned given quantity of A. erzelius.) Thus 6 carbon combine with 8 and 2.8 oxygen; 16 sulphur th 8, 2.8, 2.8 and 3. 8 oxygen; 14 nitrogen with 8, 2.8, 3.8, 4.8 and 8 oxygen; 103.8 lead with 8, 13.8 and 2.8 oxygen. This law affords a eck on the results of experiment: thus if experiment had indicated that carbon unite with 8 oxygen to form carbonic oxide, and with 15:5 ygen to form carbonic acid, it might have been suspected, since 15.5 is t one of the multiples of 8 by 14, 14, 2, 2, 3 ...., that the comsition either of carbonic oxide, or of carbonic acid, or of both, had not en correctly determined by experiment. SECOND LAW, RELATING TO DIFFERENT BODIES. From the proportion which A combines with B on the one hand and with C on the other, may kewise be calculated the proportion in which combination may take place tween B and C. If, for example, experiment shows that 1 part of A mbines with 3 parts of B and with 8 parts of C, then B and C must mbine either in the proportion of 3 B to 8 C, or in some other proporon in which the 3 B are multiplied by one of the following numbers, 1, , 2, 24, 1, 3, 4, 5, &c., or the 8 C by one of the same numbers, or the 3 B one and the 8 C by another number of the same series. The same law lds good in the case of any number of bodies, so that if 1 A will combine ith 3 B, 8 C, 10 D, 12 E, &c., then B will combine with C, D and E either in the proportion of 3 : 8, 3: 10, 3: 12, or else in proportions obtained by multiplying one or each of these numbers by some factor taken from the above-mentioned series. Taking sulphur for the body denoted by A, we find that 16 sulphur with 103.8 lead form sulphuret of lead; with 24 oxygen, sulphuric acid; with 1 hydrogen, hydrosulphuric acid; with 3 carbon, bisulphuret of carbon; and with 13.6 iron, ironpyrites. Now 103.8 lead combine, not with 24 oxygen, but with 8 oxygen to form yellow oxide of lead; the 103-8 lead must therefore be multiplied by 3 to give the proportion in which lead and oxygen are combined in the yellow oxide. Oxygen and hydrogen combine, not in the ratio of 24:1, but of 8: 1 or 24: 3; the 1 hydrogen must therefore be multiplied by 3.-24 oxygen combine not with 3 carbon, but with 18 carbon in carbonic oxide: the 3 carbon has therefore to be multiplied by 6.-24 oxygen combine not with 136, but with 81.6 iron to form protoxide of iron, the latter number being equal to 6 times 13.6. From these two laws it follows that to every simple substance there belongs a certain relative weight, according to which it combines with given relative weights of other simple substances, only that in many cases this relative weight requires to be multiplied by some number of the series already mentioned. This determinate relative weight of a body is by those who admit the atomic theory, called the Atomic Weight; by those, on the other hand, who either reject this theory altogether, or regard it as not sufficiently established, the Combining Weight, Chemical Weight, Chemical Equivalent, Combining Proportion, Equivalent Proportion, or Equi valent Number, Stoichiometrical Proportion, or Stoichiometrical Number. The origin of these two laws is most satisfactorily explained by the atomic theory (which we shall hereafter develop more completely), according to which every simple substance consists of very small invisible particles called atoms, these atoms being of uniform weight and volume in each individual substance, while the atoms of different substances may be of different weight and volume. It is assumed that in chemical combination the heterogeneous atoms lay themselves close together, and so form compound atoms, which, when collected into a mass, constitute the new compound: further, that the atoms have a tendency to unite in sigh ple numerical proportions: e. g., 1 atom of A with 1, 2, 3, or more ato of B; or 2 atoms of A with 3 or 5 atoms of B, or 3 atoms of A with 4 atoms of B. It is only in organic compounds that more complex propr tions occur. If we now examine the preceding examples according to this vie we may assume that the absolute weight of an atom of carbon is that of an atom of oxygen 68, and that 1 At. carbon combin either with 1 At. oxygen to form carbonic oxide, or with 2 At. oxyg to form carbonic acid. It will then follow that in carbonic oxide eve 6 parts by weight of carbon are combined with 8 parts of oxyge and in carbonic acid, every 6 parts of carbon with 16 of oxygen.-W may also with great probability assume that the atomic weight of sulph is twice as high as that of oxygen, and therefore 16, if that of oxyg be taken = 8. Since now, according to experiment, 16 parts of sulph can combine with 8, 16, 20 or 24 parts of oxygen, it follows that 1 A sulphur combines with 1, 2, 2 and 3 At. oxygen; and since ha atoms are inadmissible, the combination of 16 sulphur with 20 oxyge (= 32:40) may be regarded as consisting of 2 At. sulphur combins with 5 At. oxygen.-If the atomic weight of nitrogen be taken equal to 14, it will be found that 1 At. nitrogen can combine with 1, 2, 3, 4 = J. Dumas, on Isomerism. Ann. Chim. Phys. 47, 324; also Pogg. 26, 315. Spec. Gr. of Vapours. Ann. Chim. Phys. 50, 170. Leçons sur la Philosophie Chimique. Paris. Thomas Graham. Elements of Chemistry. London, 1838. Translated into German by Otto. Braunschweig, 1840. J. Persoz. Introduction à l'Etude de la Chimie Moléculaire. Paris et Strasbourg, 1839. Frankenheim, on Isomerism. J. pr. Chem. 16, 1. Pogg. 49, 341. H. Kopp, on the Relation between the Atomic Weights and Spec. Gr. of Pogg. 50, 552; 52, 269 and 282. Synonymes: Chemical Attraction, Chemical Force, Elective Attraction, Elective Affinity, Chemische Kraft, Verwandtschaft, Wahlverwandtschaft, Wahlanziehurg, Affinitas, Attractio Electiva, Affinité. History. Chemical combination was in early times attributed to the general principle of Hippocrates that like assorts with like: hence the word Affinity (Verwandtschaft) which seems to have been first employed by Barchhusen. Becher assumed, in accordance with this dogma, that when two bodies are capable of combining they must contain a common principle. Others, among whom was Lemery, supposed that solvents are furnished with a number of sharp points by means of which they are more or less adapted to insinuate themselves into the pores of solid bodies and combine with them. According to Stahl's theory, chemical combination proceeds from the intimate approximation of the parts of the combining bodies but not exactly in the manner of a wedge. Newton was the first ho referred chemical combination to the principle of universal attraction, hough he at the same time partly assumed that this attraction between Cltimate particles is not exactly the same as that which acts between the reat bodies of the universe. Geoffroy the elder, in 1718, drew up the irst Table of Affinity, which was subsequently enlarged and corrected by Gellert, Wenzel, Bergman and Guyton-Morveau. The idea that many Lhemical combinations take place in definite proportions only had occurred o some of the older chemists, e.g., Wenzel, Bergman, Kirwan; and they endeavoured to determine these proportions. This view was confirmed by Richter, Proust, Gay-Lussac, Dalton and Berzelius, and expanded Into the Theory of Definite Proportions or Stoichiometry. I. FUNDAMENTAL NOTION OF AFFINITY. Affinity is that kind of attraction by virtue of which bodies of dissimilar nature combine together into a whole which appears perfectly niform to the senses, even when assisted by the most powerful instruments. The act of union is called Chemical Combination*, the resulting product a Chemical Comopund, and if it be fluid, a Solution. The dis *The term Combination is sometimes also applied to the resulting product: the orresponding German word Verbindung is applied indiscriminately to the act of combination and to the product. [W.] VOL. I. D similar substances contained in the compound are its Components or Elements; and of these if one be fluid and the other solid, the former is called the Solvent or Menstruum, the latter the Dissolved body or Solutum. The sphere of action of chemical affinity has by some chemists been too much enlarged, by others too much contracted. An instance of the former of these errors has already been given in speaking of the mixture of gases (page 21). The following views on the contrary appear to restrict the idea of a chemical compound between too narrow limits. 1. Many combinations of liquids with gases in which the latter lose their gaseous condition are by Dalton and others regarded as mechanical (vid. Water). 2. All mixtures of liquids one with another, and all solutions of solids in liquids, are by Berzelius, Mitscherlich, Dumas, and others of the most distinguished modern chemists, regarded as not chemical, unless they take place in definite proportions: e g., mixtures of water and alcohol, alcohol and volatile oil; solutions of acids, alkalies and salts in water, alcohol, &c. Mitscherlich attributes such combinations to adhesion, Berzelius to a modification of affinity,-while, according to his view, chemical combinanations properly so called result not from affinity but from electrical attraction. Dumas ascribes them to a solvent power which he supposes to hold a middle place between cohesion and affinity: inasmuch as the former causes the union of bodies of the same nature, the latter that of bodies of very opposite natures, producing compounds possessed of new and peculiar properties; while the solvent power causes the combination of bodies of very similar nature, as of metals with metals, acids, alkalies and salts with water, resin and fat with alcohol, &c. These views lead to no satisfactory definition of Affinity (for objections to them, vid. Gehler's Phys. Wörterbuch. Ausg. 2, 9, 1862). They are nevertheless true in this respect that a distinction must be made between strong and weak affinities, the former producing compounds of definite constitution and characterised by distinct and remarkable properties, while the latter gives rise to products of less definite composition and differing less in thei properties from the bodies of which they are formed: on this ground Berthollet, in an earlier state of the science, distinguished the mor intimate combinations as Compounds (Combinaisons) and the less intimates as Solutions (Dissolutions), though the two classes merge into one another by imperceptible gradations and admit of no determinate separation. II. RANGE OF AFFINITY. may Every simple, i.e., hitherto undecomposed body, is capable of entering into chemical combination with others, but generally speaking not with all. It is possible that every simple substance may have affinity for every other; but many compounds of these substances may not have been obtained hitherto, because the components have not been placed under the particular conditions in which their affinity can exert itself; others it be impossible to form because the affinity between their components is overcome by the force of gravitation, cohesion, or elasticity. For example, the fact of carbon not combining with mercury may perhaps be explained partly by the great cohesion of carbon, the tendency of its particles to remain combined amongst themselves being possibly greater than their inclination to unite with those of mercury; partly from the greater specific gravity of mercury, by which that substance is prevented from diffusing itself through so comparatively light a body as carbon. |