448 Browning and Palmer — Ferrocyanides, etc. 



Art. XLII. — A Method for the Qualitative Separation and 

 Detection of Ferrocyanides, Ferricyanides and Sulphocyan- 

 ides ; by Philip E. Browning and Howard E. Palmer. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clviii.] 



The ordinary method for the detection of ferrocyanides, fer- 

 ricyanides and sulphocyanides by means of ferric and ferrous 

 salts leaves little to be desired in point of delicacy when these 

 substances" are not present together. When mixtures are to be 

 examined, however, the colors tend to mask one another and 

 various methods to obviate the difficulty have been suggested, 

 such as the bleaching of the red ferric sulphocyanide by mer- 

 curic chloride in testing for ferrocyanide, and the distillation 

 of sulphocyanic acid before testing for that acid. In testing for 

 a ferrocyanide in the presence of a ferricyanide the formation 

 of the deep blue color with the ferric salt or ferrous salt has 

 generally been considered of sufficient delicacy for all practical 

 purposes. 



The work to be described is the result of an attempt to 

 eifect a separation of these substances one from another as well 

 as to accomplish their detection. 



Potassium ferrocyanide has long been mentioned as a precip- 

 itant of the ferrocyanides of the rare earth elements, cerium, 

 thorium, yttrium, zirconium, etc., while it is also known that 

 ferricyanides of these elements are soluble. These facts sug- 

 gested the use of a member of the above mentioned group as 

 a precipitant of the ferrocyanogen ion and selection was made 

 of a soluble salt of thorium as perhaps the most satisfactory 

 and available. 



A solution of potassium ferrocyanide was made by dissolving 

 one gram of the salt in a liter of water, and measured portions 

 of this solution were used when amounts of live milligrams or 

 less were required. This solution was neutral to litmus and 

 remained so throughout the investigation, as shown by fre- 

 quent tests. 



The delicacy of the reaction was tested by adding to por- 

 tions of the solution enough water to make the total volume 

 between 5 cm3 and 10 cm3 , acidifying faintly with acetic acid or 

 hydrochloric acid and adding a few drops of a 10 per cent 

 solution of thorium nitrate. Amounts of the ferrocyanide as 

 small as 0*0001 grm. gave a distinct cloudiness to the solution. 

 Similar experiments made in the presence of 0*1 grm. of 

 potassium ferrocyanide and 0*1 grm. of potassium sulpho- 

 cyanide showed that these salts did not interfere with the 

 delicacy of the test. In order to test the effect of dilution 

 and the highest delicacy of the reaction, some precipitations 



