Tables of affinities

Some Theoretical Aspects of Eighteenth-Century Tables of Affinity - I, Ann. Sci. 18 (1962) 177-194 at 191. See also Alistair M. Duncan, Laws and Order in Eighteenth-Century Chemistry (Oxford Clarendon Press, 1996), 192 IF. 

While Lavoisier was perfecting a new chemistry in the 1780s, he felt obliged to offer an account of the affinities of various substances with oxygen whose properties and behavior dominated his antiphlogistic doctrine. Early in the paper he speaks of the shortcomings of the traditional tables of affin-... 

A third imperfection of the tables of affinity is that they cannot express the variation in the force of attraction of the molecules of bodies by reason of the different degrees of saturation. There are certain combinations for which there are two or three degrees of distinct saturation others for which there are an even greater number the formation of acids furnishes a large number of examples, and it will not be useless to pause here a moment. 

Nine elements were known in ancient times gold, silver, iron, mercury, tin, copper, lead, carbon, and sulfur. Bismuth, zinc, antimony, and arsenic were isolated in the alchemical period and Middle Ages. It was known that certain substances combined into other substances before the modern idea of elements and compounds was established. In 1718, Etienne Francois Geoffioy (1672—1731) presented a Table of Affinities to the French Academy of Science that summarized which substances were compatible with each other and combined to produce other substances (Figure 1.2). 

Figure 1.2 Geoffrey s Table of Affinities. Source Edgar Fahs Smith Collection, University of Pennsylavnia.

The tables of affinity which they constructed were the... 

Lavoisier then cites verbally from liis Memoire presented to the Academie des Sciences in 1782, in which that table of affinities was first printed. In this treatment, he begins by stating that he is not ignorant of the difficulties involved in making a table of affinities. And first, he says, all such tables represent only simple affinities while we recognize that there exist cases of double, triple, and much more complicated affinities. Next, the influence of tempera ... 

A second fault of our tables of affinity is that they take no account of the influence of the attraction of water, and perhaps even of the decomposition of water in reactions by the wet way, because that acts as a real disturbance which ought to enter into account. 

This which I have said against the tables of affinity in general naturally applies to the one I am presenting, but I think, nevertheless, that it may have some utility at least in so far as the more numerous experiences and the applications of calculation to chemistry place us in position to carry forward our views. Perhaps some day the precision of the data will lead to the point that the mathematician will be able to calculate in his study the phenomena of any chemical combination whatsoever, in the same manner, so to say, as he calculates the movement of the celestial bodies. ... 

The following is his table of affinities, interesting as being the list, as he says, of nearly all the substances with "which oxygen combines. The arrangement is in the order of decreasing affinities toward oxygen. 

The creation of tables of chemical affinities was an attempt to encapsulate all possible reactions between the constituents of chemical compounds. The goal was not only to provide a summary and key to known reactions but also to predict reactions that had not yet been observed. Tables of affinities thus had both a descriptive and a predictive role they could be used as a shorthand for a description and classification of observed reactions, and they could function as instruments of discovery. It was also possible, although not necessary, to use affinity tables as a clue to the mechanism of chemical reactions. It was along... 

Information about chemical theory is easier to come by than information about chemical practice. Nonetheless, we should recognize that when chemists read tables of affinities, they had in mind not only the substances that would be produced but also the ways in which the appropriate reactions could be generated and controlled. So their explicit classification of substances through affinities was joined to an implicit classification of chemical operations. Chemical operations depend on chemical apparatus, some built for that purpose, and some available in any kitchen. 

What I have said against the tables of affinities in general naturally applies to what I am going to present but in doing so I do not think less that they could... 

As all tables of affinity have been formed on the supposition that, substances are endued with different degrees of affinity, from which originate all the... 

Side by side, theories of chemical affinity -the "force" causing reactions - developed-Affinity was considered in terms of Newton s ideas (which were gaining wide acceptance at the time for explaining physical phenomena) that every particle of matter was endowed with a certain attractive force that uniguely caused all its chemical and physical reactions. To make the concept generally useful, chemists felt the need to draw up tables of affinity that would express the reactivity of individual compounds toward each other. They also hoped that such tables could be used to predict the reactivity of other compounds in similar reactions. 

Geoffroy s Table of Affinities. (From Memoires de I academie roycde des sciences, 1718, p. 212.)... 

Table of Affinities taken from Recueil de Dissertations Physico-Chimiques Presentes a Differentes Academies... 

Meyer s theory was essentially the reverse of Black s. Meyer s acidum pingue ( fatty or oily acid ) was said to be a component of all acids. When the mild alkalis (which Black understood to be carbonates) were reacted with acids, the effervescence indicated absorption of the acidum pingue found in all acids. Caustic alkalis were, as noted above, saturated with acidum pingue and thus did not effervesce when reacted with acids. The slippery feeling of caustic alkalies arose from the oily acid saturating them. Figure 178 depicts a table of affinities with acidum pingue. 

But what works they were In his first paper, published in 1766, Cavendish employed the pneumatic studies of Stephen Hales and Joseph Black to isolate hydrogen gas by pouring acids on metals such as zinc, copper, and tin. Indeed, the well-known affinities of these baser (more active) metals (see Geoffroy s Table of Affinities in Figures 175 and 176) for acids were long known to produce calxes. Moreover, the amount of gas collected did not depend on the identity of the acid (hydrochloric or sulfuric) or its amount but only on the quantity of metal. Thus,... 

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