double affinity, since these results depend, not alone on the sum of the magnitudes of affinity, but also on cohesion, temperature, and the nature of the solvent.

B. Attempts have been made to determine the relative strength of affinity of two bodies from their force of adhesion. Guyton-Morveau regarded adhesion as a commencing affinity; supposing that heterogeneous substances attract each other in masses before the attraction between their individual atoms comes into play and forms chemical compounds. The greater therefore the affinity between two bodies, the greater should also be their adhesion, and the magnitude of the former should also be determinable from that of the latter. Morveau suspended a metal disc one inch in diameter from one of the arms of a balance, and counterpoised it by weights in the opposite scale; he then placed under the disc a glass filled with mercury, so that the surface of the mercury just came in contact with the lower surface of the disc,-and ascertained what additional weight required to be laid in the opposite scale-pan in order to separate the disc from the mercury. In this manner he found that the following weights were necessary: gold 446 grains, silver 429, tin 418, lead 397, bismuth 372, zinc 204, copper 142, antimony 126, iron 115, cobalt 8. This is almost exactly the order of facility in which these metals combine with mercury, and so far experiments appear to accord with the preceding view. But it has not yet been shown that the magnitudes of adhesion and affinity are in direct proportion one to the other. Although the affinity of sulphur for mercury is much greater than that of either of the metals just named, still a disc of sulphur would adhere to it with far less force than either of the metallic discs did. Moreover, the fact of mercury combining with gold more easily than with zinc does not show that gold has the greater affinity for the mercury: for facility of combination is one thing, intimacy another. Besides, Morveau's method does not give even the force of adhesion; for a certain quantity of mercury remains attached to the plates, and on separation the mercury itself is torn asunder, and the force determined is in reality its cohesion. Finally both on this ground, and because many substances on coming in contact immediately enter into chemical combination, and the film of the new compound of the two bodies whose adhesion is to be measured is really that which suffers disruption,-an exact determination of the force of adhesion in the most numerous and important cases is impossible.

C. The strength of affinity is sometimes estimated by the time in which combination takes place. Wenzel (Von der Verwandtschaft, p. 28) exposed metal cylinders of equal height and diameter, and covered all over, with the exception of one of the terminal surfaces, with varnish -to the action of different acids at the same temperature and for equal intervals of time, and estimated the force of affinity by the quantity of inetal dissolved. These experiments however prove nothing, first because in the solution of metals in acids various affinities come into play, viz., the affinity of the metal for oxygen, which has to be taken sometimes from the acid sometimes from the water, that of the oxide of the metal for the acid-and that of the salt for water; secondly, because Wenzel sometimes used concentrated, sometimes dilute acids, according to the condition of the metal-and thirdly, because a given surface of different metals exposes a different number of atoms to the action of a solvent, according to the atomic weights and densities of the metals. But even experiments in which these sources of error were eliminated would lead to nothing, because the important influence which cohesion, specific gravity,

&c. exert on the rapidity of the combination could not well be taken into

account.

D. Strength of affinity has been estimated from the quantities in which bodies combine.

Berthollet laid down the following hypothesis: The smaller the quantity of a body B required to neutralize another body A, that is to say to balance its opposite properties, the more completely opposite must B be to A, and the greater must therefore be their mutual attraction. If for example a certain quantity of an acid is neutralized by 1 part of the base B, but requires 2 parts of the base C and 3 of the base D, the affinities of A to B, C, and D = 3 : 14 : 1; in short, the force of affinity is inversely as the quantity required for neutralization. A similar relation exists with regard to the affinity of a base for several acids; that acid of which the smallest quantity suffices for the neutralization of the base, will have, of all acids, the greatest affinity for the base. This view of the matter is contradictory to the order of affinity found from decompositions by double affinity. For example, 40 parts of sulphuric acid are neutralized by 766 baryta, 52 strontia, 47.2 potash, 31-2 soda, 28.5 lime, 20-7 magnesia and 17 ammonia; and 28.5 lime are neutralized by 40 sulphuric acid, 54 nitric acid, 36-4 hydrochloric ric acid, 127 hydriodic acid, 32 sulphurous acid, and 22 carbonic acid. The bodies here follow in the order in which they separate each other, so that for example baryta takes sulphuric acid from all other bases aud sulphuric acid takes lime from all other acids. The law here manifested -that, for the most part, those substances of which the smallest quantities are required to neutralize a third body-and which should therefore have the greatest affinity for that body-are separated by those which combine with the same body in greater proportion, and should therefore have less affinity for it-is explained by Berthollet from the influence of cohesion and elasticity. According to that philosopher ammonia has, of all the bases here enumerated, the greatest affinity for sulphuric acid, for it is the base of which the smallest quantity is required to neutralize that acid: that it should however be separated from sulphuric acid by all other bases arises from its tendency to assume the gaseous form. From the same cause the highly elastic substance carbonic acid, which of all acids has the greatest affinity for lime, is separated from that base by hydrochloric acid: (the incorrectness of this explanation is manifest from the experiment described p. 130). That baryta should take sulphuric acid from all other bases, although according to Berthollet's view its affinity for that acid must be the smallest, is explained by the great cohesion of sulphate of baryta: and that potash should separate lime and magnesia is supposed to result from the great cohesion of those earths, &c. It is certainly worthy of remark that when an acid is brought in contact with two salifiable bases, the least soluble body is always obtained: if one salt is less soluble than another, it is formed; if one base is less soluble than another, it is precipitated. Thus baryta takes sulphuric acid from strontia and forms with it an insoluble salt; strontia withdraws sulphuric acid from potash, and potash from soda,-sulphate of strontia being less soluble than sulphate of potash, and sulphate of potash than sulphate of soda. Soda takes lime from sulphuric acid, and the lime which separates is the least soluble body; lime takes sulphuric acid from magnesia, and magnesia is less soluble than lime. Ammonia alone forms an exception: it gives up sulphuric acid to lime, and the lime is thereby converted into the more soluble sulphate of lime. When a base comes in contact with

two acids, the same effect often takes place; sulphate of baryta is less soluble than nitrate, and this than hydrochlorate of baryta, &c.

the other hand, the almost insoluble sulphite and carbonate of baryta are decomposed by nitric acid.

Bergman deduced from his analyses of various salts the two following laws which are directly opposed to Berthollet's theory: (1.) An acid has the greatest affinity for that base of which it takes up the greatest quantity. (2.) A base has likewise the greatest affinity for that acid of which the greatest quantity is required to neutralize the base.

Kirwan, from the results of his own analyses of salts, adopted the first of Bergman's laws; but with respect to the affinity of a base for different acids, he on the contrary laid down the law, that a base has the greatest affinity for that acid of which it takes up the smallest quantity.

All these laws could only have acquired an appearance of validity from the fact, that but a small number of acids and bases were examined in relation to them, and moreover in an inaccurate manner. Adopting the more exact quantitative relations at present known, and placing all the salifiable bases,-including those of the heavy metallic oxides-in the sulphuric acid column, and all the acids in the lime column, it will be plainly seen that decomposition by simple affinity has no fixed relation to proportional quantity. Moreover we now know that the latter depends on the atomic weight of bodies. If then the strength of affinity were determined by relative quantity, the former would bear a simple proportion, direct or inverse, to the atomic weight. Accordingly to Berthollet's law, the affinity of hydrogen for other bodies should be the greatest of all, since hydrogen has the smallest atomic weight, and therefore the smallest quantity of it suffices to saturate other bodies; the affinity of iodine on the contrary ought to be less than that of most other bodies, sulphur for example, since 126 parts of iodine are necessary to saturate a quantity of metal for which 16 parts of sulphur are sufficient; nevertheless iodine, though more volatile than sulphur, decomposes the metallic sulphurets.

General Laws, by which the Magnitude or Strength of Affinity is

regulated.

1. With regard to the same two bodies. If A combines with different quantities of B, it holds the first quantity of B with greater force than the second, the second with greater force than the third, and so on. This law holds good without exception.

Carbonic acid, C O, in contact with hydrogen gas, zinc, iron, &c. at a red heat, gives up only 1 atom of oxygen, the other remaining-in consequence of the superior affinity of the carbon-united with it in the form of carbonic oxide, C O. Brown peroxide of lead, Pb O2, is reduced at a low red heat to red lead, Pb3 O', oxygen gas being evolved; the red lead at a stronger red heat gives up more oxygen and is converted into the yellow oxide, Pb O; and this will not part with its one atom of oxygen even at the most intense heat, but sublimes unchanged.

Apparent exceptions: Many combustible bodies abstract oxygen from nitrous oxide, N O, at a lower temperature than from nitric oxide, N 02, This anomaly must be attributed to the hindrances which the gaseous state offers, in various degrees, to chemical action. The fact that nitric oxide is deprived of its second atom of oxygen by alkaline sulphites, and converted into nitrous oxide which suffers no further alteration from the

action of the same salts, proves the correctness of the law.-Nitric acid, N O3, does not give up its oxygen to many bodies so easily as hyponitric acid, NO. But nitric acid, precisely on account of the small affinity of the nitrogen for the last atom of oxygen, is not known to exist in the separate state, but only in combination with water or salifiable bases. In aqueous nitric acid the great affinity of the water for the acid opposes, to a certain extent, the transfer of the oxygen to other bodies. So likewise hyperchlorate of potash, K O, CI O, is less easily decomposed by heat and combustible bodies than chlorate of potash, K O, Cl O3, although it contains two more atoms of oxygen. But hyperchloric acid is just on account of this greater quantity of oxygen a stronger acid than chloric acid, and the consequent greater affinity of potash for hyperchloric acid renders its decomposition more difficult.

2. With regard to different bodies. (a.) Simple substances exhibit the strongest affinities for each other, e. g. oxygen, chlorine, bromine, iodine, &c. towards most other elements. Then follow compounds of the first order, e. g. acids and salifiable bases. The affinities of compounds of the second order, salts, for instance, are much weaker. In proportion as the affinities of the elements are satisfied by combination, their tendency to form further combinations diminishes and ultimately ceases.

b. The more opposite bodies are in their physical properties, the greater for the most part is their affinity. Thus, metals being similar bodies have generally but little affinity for one another, but great affinity for oxygen, chlorine, bromine, iodine, sulphur, and other non-metallic bodies; in a similar manner, acids have little affinity for other acids or bases for other bases, but the affinity between acids and bases is very strong.

Columns of Affinity.

The following are a few columns of affinity drawn up principally from decompositions by simple affinity and from analogical reasoning. From the difficulty of the subject they must be considered as merely rough approximations. The bodies separated only by a comma are those whose relative position is as yet undecided; after each semicolon are placed substances whose affinity is decidedly weaker.

Oxygen: K; Na, L?; Ba, Sr, Ca; Mg, Ce, Y, G, Al, Th, Zr, Si; Ti, Ta, W, V, Cr, Mn; CO, H; Mo; Zn; Fe; Cd; Ni; Co; Sn; U; Ta O2; Mn O; Mo O; TiO; P; Pb; Bi; Sb; PO3; S; Cu; Mo 0; As; N; Sn O HCI; S O; W O; N O; Se; Pt Ir; Fe 0 S 03; Hg; Te; Os; R; Pd; Ag; K O; Ba O; As 03; I: NO1; Cr2 03, V2 03; Au; Br; Cl; F; I 03; CIO3; HO.

Chlorine: K and the other alkaline metals; metals which are the bases of the earths; Ti; Zn; Fe; Cd; Co; Sn; CO; H; P; Pb; Bi; Sb; S; Hg; As; Ag; Sn Cl; Hg Cl; Pd; Pt; Au; I; Br; O.

rine.

Fluorine, Bromine, and Iodine are similar in their relations to chlo

Sulphur: 0; K and the other alkaline metals; Zn, Fe; Sn; Cu; Cl; H; C; Pb; Bi; Sb; Hg; Ag; Pt; Cu S; Mo S2; Au.

Phosphorus: 0; Cl; Br; I; K; Zn; S; H.

Hydrogen: 0; F; Cl; Br; I; Se; S; P; As; Sb; N.

Nitrogen: C; H; I; Br; Cl.

Metals: 0; F; Cl; Bs; I; Se; P; H. It is true that many metallic oxides and fluorides are decomposed at a red heat by chlorine; but in such cases the affinity of heat for the more volat Substances, oxygen and

fluorine, must be taken into account. Nevertheless the affinity of the noble metals for chlorine seems to be greater than for oxygen. On the whole it appears that different metals have different orders of affinity.

Sulphuric acid: Ba O; Sr 0; KO; Na O; LO? Ca O; Mg O; Pb 0; N H3; Fe 0; Zn 0; Ni 0; Co 0; Cu 0; A12 03; Fe2 0. Comp. Shnaubert (Unters. der Verwandtsch, 57); Karsten (Scher. 5, 583); GayLussac (Ann. Chim. 89, 21.)

Hydrochloric acid: 4Pb 0; K 0; Na 0; Ba 0; Sr 0; Ca O; Mg 0; N H3; Co 0; Ni0; Hg O; Ce O; Zn O; Mn O; Fe 0; U 0; Au03?; Cu2 O; Cu O; Sn O; GO; Al2O3; U2 03; Cr2 03; Fe2 03; Sn O2; Bi2 0, Sb O3. Comp. Schnaubert; Anfrye and Darcet (A. Gehl, 3, 325), GayLussac, a. a. O., and especially Persoz (Ann. Chim. Phys. 58, 180, also J. Pr. Chem. 6, 32). Persoz places the suboxide of copper above the protoxide, without however resting his supposition on experiment, and perhaps incorrectly. With regard to 4Pb O, vid. page 139.

Nitric Acid: KO; Na O; L O?; Ba O; Sr 0; 6Pb 0; Ca O; Mg 0; N H3; Ag O; Co 0; Ni 0; Ce O; Zn O; Mn O; Cd O; (6Pb O, NO3); Cu O, G 0; Al2 03; U2 03; Cr2 03; Hg20; Hg 0; Fe2 03; Bi2 03; according to Schnaubert, Gay-Lussac, Anfrye and Darcet, and particularly according to Persoz. Here also the place assigned by Persoz to suboxide of mercury above the protoxide is to be doubted; according to Proust, (A. Gehl, 1, 525) protoxide (red oxide) of mercury stands likewise above protoxide of copper, and according to Schnaubert, protoxide of manganese precedes protoxide of nickel.

For phosphoric acid the order appears to be as follows: Baryta, strontia, lime, potash, and soda; and for oxalic acid: Lime, baryta, strontia, magnesia, potash, soda, ammonia.

In the revision of these columns of acids particular attention should be paid to the formation of basic salts.

Potash: 2 At. Mo 03; 2S O3; 2Cr 03; 2 At. oxalic acid: 2 At. tartaric acid; S O3; Se O; N 05; I 0'; C1 07; H F; H Cl; P 05; As O5; I 03; Br 03; Cl O3; H Br; Cr O3; P 03; HI; Se O2; N O3; Mn O'; Mn O5; BO3; CO2; As O3; H Se; HS; HCy. This column is as yet very uncertain, and requires many corrections and additions.

Other bases exhibit orders of affinity more or less resembling that of potash.

VI. ORIGIN And Nature of THE PHENOMENA OF AFFINITY.

1. Atomic Hypothesis.

According to the Atomic or Corpuscular Theory, matter is an original essence, and consists of certain very small parts called Atoms, Molecules, or Particles, arranged, not in absolute contact, but with Intervals or Pores between them; so that bodies, which to the eye appear perfectly continuous, like a piece of glass or metal, must be regarded, not as being completely filled with matter, but as aggregates of atoms and empty spaces. In chemical combination the heterogeneous atoms arrange themselves close to each other, but without penetration-juxtaposition takes placeand the aggregate of the so formed compound atoms, with the intervals or pores between them, constitutes the new compound. The ancient and modern atomic theories are distinguished from one another, according to the force which is supposed to act in bringing about the juxtaposition of the heterogeneous atoms.

VOL. I.