Royal Society. 537 



position of some terms in the series, but hydrosulphocyanic acid 

 certainly had the least affinity for ferric oxide in comparison with 

 potash : it was represented by unity : the other acids followed in 

 the order — nitric, 4; hydrochloric, 5; sulphuric, 7; gallic, 10- 

 pyromeconic; meconic ; acetic, 20; hydrobromic ; comenamic • 

 citric, 100; hydroferrocyanic, 170. 



Other coloured salts were submitted to a more cursory investiga- 

 tion. The scarlet bromide of gold when treated with an alkaline 

 chloride gave a striking instance of the effect of mass in gradually 

 overcoming a strong affinity. The intensely red iodide of platinum 

 afforded results which, though somewhat obscure, were not opposed 

 in their testimony. So did the blue sulphate of copper when treated 

 with different chlorides. The " manganoso-manganic oxide" dis- 

 solves in sulphuric or phosphoric acid of a red, and in other acids of 

 a deep brown colour ; and it was found that hydrochloric acid was 

 capable of changing the colour of the sulphate according to its mass, 

 while on the other hand sulphuric or phosphoric acid altered in like 

 manner the tint of the chloride. Somewhat similar results were ob- 

 tained by means of the green chloride and the purple fluoride of mo- 

 lybdenum ; and the blue solution that forms when gallic acid is 

 brought in contact with both the oxides of iron at once, bore testi- 

 mony to the same general laws. The peculiar optical character of 

 certain salts of quinine was also taken advantage of for deter- 

 mining what changes took place among the compounds in solu- 

 tion. The amount of fluorescence exhibited by a solution of acid 

 sulphate of quinine was found to be affected by the admixture of a 

 chloride, bromide, or iodide according to the nature and the mass of 

 the salt added, and the addition of sulphuric, phosphoric, nitric and 

 other acids was found to produce a fluorescence in solutions either 

 of hydrochlorate of quinine, or of sulphate which had been rendered 

 non-fluorescent by hydrochloric acid. Similar results were obtained 

 with quinidine ; and somewhat analogous ones with the organic bases 

 contained in horse-chestnut bark, and in tincture of stramonium. 

 An experiment is also narrated showing that the same laws hold 

 good in respect to compound aethers as to salts having metallic 

 bases, alcohol being employed as the solvent. 



Beside the very diversified substances already mentioned in this 

 abstract, several others, such as lead, mercury, zinc, potash, soda, 

 baryta, lime, and ammonia, are shown by a more indirect proof to 

 enter into compounds which obey the same laws. Hence it is con- 

 cluded that what was observed in reference to the ferric salts holds 

 good very generally, if not universally. 



The bearing of certain other phenomena upon the question at 

 issue was also examined. The fact that precipitation, when it oc- 

 curs, gives rise to a perfect interchange of bases and acids, is equally 

 consistent with either Bergmann's or Berthollet's theory ; but not 

 so is the fact that two soluble salts cannot be mixed without the 

 occurrence of precipitation, if one of the products that may be formed 

 is an insoluble salt. The only recorded exception to this law, which 

 occurs with oxalate of iron in the presence of a salt of yttria, under 

 peculiar circumstances, was found on close examination to be in 



