299 



the requirements of the experiment, as some are intensely coloured 

 while others are nearly colourless. 



The circumstances that attended the formation of the blood-red 

 sulphocyanide were first fully examined. On mixing known quan- 

 tities of different ferric salts with known quantities of different sul- 

 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 both 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 0'194 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 



