Manchester Memoirs, Vol. liii. (1908), No. 0. 



VI. On the Production of White Ferrous 

 Ferrocyanide. 



By R. L. Taylor, F.C.S., F.I.C. 



Received and read Deceinher 13th, igoS. 



It is well known that a solution of a ferrous salt, if it 

 can be obtained free from even a trace of a ferric salt, gives 

 a white precipitate when a solution of potassium ferro- 

 cyanide is added to it. But there is such great difficulty 

 in obtaining a ferrous solution entirely free from ferric 

 that very few chemists have ever seen pure white ferrous 

 ferrocyanide. The precipitate usually obtained is a blue 

 one — lighter or darker in colour according to the amount 

 of ferric salt present — and consists of a mixture of the 

 white ferrous compound with more or less Prussian blue, 

 which is the very dark blue precipitate produced b)- the 

 action of ferrocyanide of potassium on a ferric solution. 

 None of the ordinary reducing agents will deprive a 

 solution of a ferrous salt of all trace of ferric ; but the 

 author finds that a small amount of a solution of " hydro- 

 sulphurous acid" (more correctly the genuine "hypo- 

 sulphurous acid," H2S3O4) will accomplish this. The acid 

 (mixed with some of its zinc salt) is easily prepared by 

 shaking up for a minute or two a solution of sulphur 

 dioxide in water with zinc "dust," and filtering the liquid. 

 Or a dilute solution of sodium hydrosulphite, Na^S^Oi* 

 may be used. The addition of either of these to an 



* Sodium Hydrosulphite is now a commercial substance, and is made in 

 considerable quantities. It is patented by the Badische Company Limited 

 under the name of " Blankit." In the solid state it appears to be fairly 

 stable, but it scon decomposes when in solution in water. 



December 21 sti rgo8. 



