86 Kansas Academy of Science. 



ON SOME FERROCYANIDES OF CALCIUM, BARIUM, 

 AND MAGNESIUM. 



By F. B. Dains, Washburn College, Topeka. 



WHEN potassium ferrocyanide is added to solutions of cal- 

 cium, barium and magnesium containing free ammonia or 

 ammonium salts, difficultly soluble precipitates are obtained. Con- 

 cerning the composition of these precipitates some confusion seems 

 to have arisen. The general idea has been that they were double 

 ferrocyanides of potassium and the alkaline earth metal. Tests, 

 however, showed that the product always contained ammonia; 

 hence it seemed of interest to ascertain whether the precipitate 

 was a definite chemical compound or a mixture of ferrocyanides. 



H. Baubigny, in an article on the separation of calcium, barium, 

 and strontium ( Chem. News, 72, 27), suggests that after the re- 

 moval of the barium as barium chromate, and after getting rid of 

 the excess of the chromate, the calcium be precipitated by means 

 of potassium ferrocyanide in ammonium chlorid solution. On the 

 authority of Rose, he calls this precipitate a potassium-calcium 

 ferrocyanide. He also recommends the use of potassium ferro- 

 cyanide as a test for calcium. 



In the text-book of qualitative analysis by Bailey and Cady 

 (first edition) the precipitation of calcium and magnesium by 

 potassium ferrocyanide in the presence of ammonuium salts is 

 mentioned, and the fact pointed out that they contain ammonia. 

 Recently (Jour. Am. Chem. Soc, 28, 1510) Flanders has suggested 

 the use of potassium ferrocyanide in the presence of ammonium 

 chlorid as a test for calcium, and on the authority of Prescott and 

 Johnson (1903, p. 212) calls the precipitate potassium ferrocyanide. 



EXPERIMENTAL. 



The product formed by precipitating a calcium salt with potas- 

 sium ferrocyanide in the presence of a large excess of ammonium 

 chlorid or nitrate was thoroughly washed with hot water, and dried, 

 first on a porous plate, and then at seventy degrees in an oven. 

 Qualitative tests showed that the product contained potassium, 

 ammonium, calcium, the ferrocyanogen ion, and water. Analysis 

 of various preparations gave results which correspond to the folow- 

 ing formula : K2CaFe(CN)6, 4( NH4)CaFe(CN )62H20. 



