536 Royal Society. 



phocyanides, it was found that the whole of the iron was never con- 

 verted into the red salt ; that the amount of it so converted depended 

 on the nature hoth of the acid combined with the ferric oxide, and 

 of the base combined with the sulphocyanogen ; and that it mattered 

 not how the bases and acids had been combined previous to their 

 mixture, so long as the same quantities were brought together into 

 solution. The effect of mass was fully tried by mixing equivalent 

 proportions of ferric salts and sulphocyanides, and then adding known 

 amounts of either one or the other compound. It was found that in 

 either case the amount of red salt was increased ; and that when the 

 numbers of equivalents of the salt added were taken as abscissae, 

 and the amounts of red sulphocyanide produced, as ordinates, the 

 numbers observed in the experiments gave regular curves, though 

 not belonging to the second order. The curves representing the 

 experiments in which sulphocyanide of potassium was mixed with 

 ferric nitrate, chloride, or sulphate, appeared to be the same, but 

 hydrosulphocyanic acid gave a different curve. The deepest colour 

 was given when nitrate of iron was mixed with the sulphocyanide, 

 but even upon the admixture of one equivalent of the former with 

 three of the latter, only 0T94 equiv. of the intensely red ferric salt 

 was formed, and when 375 equivalents of sulphocyanide of potassium 

 had been added there was still a recognizable amount of nitrate of 

 iron undecomposed. It was found that the addition of a colourless 

 salt not only reduced the colour of a solution of ferric sulphocyanide, 

 but also that the reduction increased in a regularly progressive ratio 

 according to the mass of the salt. 



Other ferric salts were likewise examined. The black gallate gave 

 results precisely analogous to those obtained by means of the sul- 

 phocyanide ; the red meconate also confirmed Berthollet's views, 

 but the action of mass was rendered obscure by the formation of 

 double or of acid salts ; the red pyromeconate resembled the meco- 

 nate ; the red acetate bore similar testimony ; the blue solution of 

 the ferric ferrocyanide in oxalic acid gave results fully corroborative 

 of the influence both of the nature and of the mass of every sub- 

 stance present at the same time in the mixture ; the purple and the 

 red comenamate afforded similar results ; while the red bromide 

 (not the oxybromide), though somewhat indistinct in its testimony, 

 corroborated to a certain extent the preceding observations. 



Experiments were performed with a view to determine what effect 

 the mass of water might have on the salts operated upon ; its influence 

 in reducing the colour of the ferric sulphocyanide was found to be 

 very great, but the nature of it could not be exactly determined. 

 As however it was uniform in its action in whatever manner the 

 sulphocyanide had been produced, it could not affect the results of 

 the preceding experiments. Water did not appear to act in any- 

 similar manner upon the other ferric salts. 



From the mass of quantitative observations made during the inves- 

 tigation, it was possible to deduce not only the order of affinity of 

 the various acids for sesquioxide of iron as compared with potash, 

 but also to assign approximative numbers. Doubt may rest on the 



