Elective Attractions

In his Elective Attractions, Torbern Bergman stated emphatically that the so-called sedative salt is not a salt but an acid. The substance commonly called sedative salt, said he, is more nearly allied to acids than any other class of bodies. It reddens turnsole and saturates alkalis and soluble earths. It also dissolves various metals, and has other properties which shew its acid nature, and it seems better entitled to the name of acid of borax than to that of sedative salt (66). 

Bergman, T., A dissertation on Elective Attractions, J. Murray, London,... 

Second, note that Lemery here shows awareness of what is later called affinity, or elective attraction the pattern of behavior where one substance shows a particular chemical preference by leaving its combination with one body to attach itself to another. In this case the acid has a greater affinity for the quicklime than for the mercury, hence joins the lime and leaves the mercury to be volatized and driven forth as a spirit. You may ask. Where was the acid that Lemery speaks of It is a component part of the mineral... 

We have seen already in Lemery s Cours de chymie of 1675 examples demonstrating his implicit use of elective attraction. Others have traced the replacement of one metal by another at least as far back as Glauber before the middle of the 17th century. Chymists were aware of this elective behavior for a long time, and used it as a kind of explanation long before Geoffroy systemized the phenomena in 1718 in a truly functional way. 

It was not long before this empirical concept of chemical affinity became associated with the concept of Newtonian short-range interparticle forces, an identihcation best expressed in Bergman s 1775 monograph, A Dissertation on Elective Attractions, and in attempts, now known to be flawed, by such chemists as Guyton de Morveau, Wenzel, and Kirwan to quantitatively measure these forces—attempts which also culminated in an early precursor of the chemieal equation known as an affinity diagram (Figure 3). 

Bergman describes at length the preparation and properties of carbonic acid salts, with determinations by weight of the quantities of acid and base (these not always accurately, however). He also determined the relative elective attractions of the acid for different bases. His order of such affinities is as follows ... 

After everything I think I may now voice the assertion that, in the formation of these images a new, hitherto unknown force is active. It has nothing in common with magnetism, electricity or Galvanism. It is not excited or fanned by something external, but inhabits the elements from the very beginning and shows itself to be effective, when these balance out their chemical oppositions, i.e., combine and separate by elective attraction and repulsion. I call this force the drive to formation and consider this to be the model of the life force that is active in plants and animals.51... 

Bergman, Disquisitio de Attractionibus Electivis, K. Ventenskaps Societeten i Upsala, Nova Acta Regiae Societatis Scientiarum Upsaliensis [2], 2, 1775, 159-248. (For an English translation, see Dissertation on Elective Attractions, tr. J. A. Schufle, Johnson Reprint Co., 1968.) An abstract appeared... 

Bergman, Opuscula physica et chemica (Uppsala, 1783), volume 3 A Dissertation on Elective Attractions (London, 1785), facsimile reproduction with... 

Bergman s original dissertation, published in Latin in 1775, is nearly identical in the order and in the content with the 1783 version. I am using the English translation of the latter version in 1785 which preserves more of the contemporary wording than Schufle s translation of the 1775 version. I have taken care, however, to compare the two versions to screen out the later additions Bergman, A Dissertation on Elective Attractions (London, 1785) reprinted with an introduction by A. M. Duncan (Cass, 1970). 

Torbern Bergmann, A Dissertation on Elective Attractions, translatedfrom the Latin by the translator of Spallanzani s dissertations (London, Murray, and Edinburgh, Elliot, 1785), translated from Disquisitio de attractionibus electivis in vol. 2 of Nova acta Regia societatis scientiarum upsaliensis (1775). The chemical essays of Charles-William Scheele. Translated from the Transactions of the Academy of Science at Stockholm, with additions by T. Beddoes (London, 1786). 

In Figure 218 and the enlargement of item 26 in Figure 219(b) is depicted a double elective attraction. Silver nitrate (1) and sodium chloride [(2), table salt] decompose each other in water (3) to produce silver chloride (4), which precipitates (downward bracket), and sodium nitrate (5), which remains in solution (upward bracket). 

FIGURE 219. (a) Single -elective attraction (decomposition) of calcium sulfide from Bergman s tables (see Figure 218). (b) Double elective attraction between silver nitrate and sodium chloride (see text). 

Elective attraction is either simple simplex) or double duplex). An example of double attraction ( V) is shown in Fig. 48 (for the symbols see Vol. II,... 

Bergman ( III) assumed that in general the series of attractions at a given temperature is constant, but they may be modified by heat and two sets of tables, for the wet and dry ways, are required. The effect of temperature on affinity is explained ( IV) Let M denote any substance attracted by two menstrua with elective attractions Ay a A>a). If the first is more volatile and its tendency to rise is V, that of the other being v, then M is attracted by a force A -a. With rise of temperature V increases faster than Vy at length A-a V-Vy and as the fire is increased the equilibrium is destroyed and the originally weaker menstruum prevails. 

Bodies have different degrees of attraction for one another, which may be determined by experiment. If a body A is presented to a compound BC four cases are possible (i) no action, (ii) A + BC = ABC (a ternary compound), (iii) A + BC = AC + B completely, (iv) A combines with part only of BC to form a compound different from ABC. Examples (iii) and (iv) correspond with Bergman s elective attraction. Double elective attractions are divided into a) A+B+CD AC+BD, and (6) AB+CD =AC +BD. Numerical examples are given. 

---