36 HISTORY OF CHEMISTRY. [LECTURE III. 



time of so-called tables of affinity. The latter were tables which 

 purported to express the strength of the affinity of substances, 

 and they had been drawn up by a large number of chemists. 

 The earliest originated with Geoffroy, 7 and dated from the year 

 1718. It consisted of various tables in which the other sub- 

 , stances were so arranged with respect to a particular one, that 

 each preceding substance always decomposed the compound 

 which the next succeeding one formed with this particular 

 substance. Thus, for example, his table for acids in general 

 ran : fixed alkali ; volatile alkali ; earths ; metals. The con- 

 struction of such tables was one of the chief occupations of 

 chemists in the middle of the eighteenth century. With them 

 they associated the erroneous view that the affinity of one sub- 

 stance towards another is invariable ; and it was only by degrees 

 that chemists were convinced that this was an error. In 1773 

 Beaume pointed out that the affinities were different at ordinary 

 and at very high temperatures (in the wet and dry ways), and 

 that for each substance it would thus be necessary to construct 

 two tables which should express its behaviour towards all other 

 substances under these two different sets of conditions. 8 Berg- 

 man undertook this task, 9 and it is truly astonishing what enor- 

 mous pains he took in carrying it out. For each substance he 

 constructed two tables, in which he compares its behaviour 

 towards fifty-eight others, and these latter were so arranged that 

 each preceding substance decomposed the compound which 

 the next succeeding one formed with the particular substance 

 concerned. From these tables it was, seemingly, possible to 

 foretell the results of all reactions ; hence they were held in 

 great esteem. When a new substance was discovered, such 

 a table of affinity was at once constructed for it, and even 

 Lavoisier respected this usage on the occasion of his investi- 

 gation of oxygen, although he pointed out at the time that a 

 similar table would really be required for every degree of 

 temperature. 10 



7 Kopp, Geschichte. 2, 296. 8 Ibid. 2, 299. 9 Ibid. 2, 301. 

 10 Lavoisier, Oeuvres. 2, 546. 



