CHAPTER XIX 



BALANCED ACTIONS 



Mayow (1674) on the displacement of nitric acid by 

 oil of vitriol. Like many other important theories, the idea 

 of reversible or balanced actions had its origin in the study of 

 acids, bases, and salts. Mayow (A.C.R. XVII, 161 ; quoted 

 on p. 22) showed in 1674 that, when oil of vitriol was added 

 to nitre, the -nitric acid could be distilled out under a heat 

 no greater than is required for the rectification of the free 

 acid. This easy distillation was explained by supposing 

 that the nitric acid had been " expelled from the society of 

 the [alkali] by the more fixed vitriolic acid." 



Similarly, it was noticed that the volatile alkali could be 

 displaced from any of its salts by the fixed alkalis, the 

 reason being given " that the acid ... is capable of entering 

 into closer union with any fixed salt than it is with a volatile 

 salt." 



Baume (1760) on the decomposition of vitriolated tartar 

 by nitric acid. Whilst nitric acid is expelled from nitre by 

 sulphuric acid with the aid of gentle heat, the opposite 

 change may take place when the mixture is kept cold. This 

 fact was discovered in 1760 by Baume, who described the 

 action as follows : 



" I took four gros of vitriolated tartar, 1 reduced to a fine 

 powder, I mixed it with three gros of very pure fuming 

 spirit of nitre ; ... the mixture became pasty, I diluted it 

 1 Potassium sulphate. 



