372 Royal Institution. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



March 31, 1854. — On Chemical Affinity among Substances in 

 Solution. By John Hall Gladstone, Esq., Ph.D., F.R.S. 



An historical sketch of the development of tlie ideas of chemists 

 concerning " affinity " was first given. The dogma of Hippocrates 

 that " like combines only with like," was shown to be superseded 

 by the view of Glauber and others, that unlike substances combine 

 most readily ; and that where two bodies have an affinity for one 

 another, it is a sign that they have no affinity with one another. 

 The views of Newton and Boyle in reference to the different degrees 

 of strength of affinity were then considered, and particular attention 

 was directed to the doctrine of Bergmann, that when a decompo- 

 sition takes place by means of the greater elective attraction of a 

 third body, that decomposition is complete. In opjjosition to this, 

 Berthollet contended that in all such cases of composition or decom- 

 position there takes place a partition of the base, or subject of the 

 combination, between the two bodies whose actions are opposed ; 

 and that the proportions of this partition are determined, not solely 

 by the difference of energy in the affinities, but also by the differ- 

 ence of the quantities of the bodies — by their physical condition, — 

 and by that of the combinations capable of being generated. These 

 views did not meet with a favourable reception at the time of their 

 promulgation ; and the attention of chemists had been drawn away 

 from the subject until within these last few years, when Malaguti, 

 Bunsen, Debus, and Williamson have published investigations bear- 

 ing upon the point. The lecturer then stated, that before any of 

 these papers had appeared, he had been thinking of and performing 

 some experiments upon the subject in question, and that he was still 

 continuing them. 



After a few experiments illustrative of " chemical combination " 

 and of "elective affinity," others were introduced to show how 

 easily this latter pliaenomenon was affected by circumstances. Thus 

 ammonia will displace alumina from a solution of the sulphate, but 

 on the other hand, alumina will displace anunonia when heated with 

 the solid sulphate of that volatile base ; whilst if solutions of chloride 

 of aluminium and sulphate of ammonia be mixed and evaporated, 

 crystals of the double sulphate, ammonia-alum, will appear. There 

 were on the table two white salts ; the one had been carbonate of 

 baryta, but by boiling with excess of sulphate of j^otash, it had been 

 converted into the sulphate ; the other had been sulphate of baryta, 

 but by long-continued boiling with much carbonate of potash, it had 

 suffered the opposite change into the carbonate. The lecturer then 

 stated that so great is the nifiueuce exerted by these various circum- 

 stances, that some have doubted whether there be a true " elective 

 affinity ; " he however believed that after making every allowance for 

 known causes there is still a residuary phsenomenon to which that 

 name is the most appropriate. Allowing then, with Bergmann, 

 that relative degrees of affinity exist, the question arises : — Is 

 Berthollet's law also correct ? It is very difficult to arrive at a 

 satisfactory answer, since it is almost impossible to eliminate 



