Browning and Palmer — Jferrocyanides, etc. 449 



were made in 100 om3 and 500 cm3 of water, and it was found 

 possible to detect 0*0005 grin, in 100 cm3 of water and 0*0010 

 gms. in 500 cm3 of water, or one part of the ferrocyanide in 

 500,000 parts of water. 



The presence of considerable amounts of alkali acetates have 

 a tendency to decompose the thorium ferrocyanide into soluble 

 products, but this tendency may be overcome by further addi- 

 tion of thorium salt or hydrochloric acid. 



Some difficulty was found in filtering the thorium ferrocy- 

 anide on paper alone, on account of its finely divided condi- 

 tion, but this difficulty was removed by agitating the liquid 

 and suspended precipitate with some finely shredded asbestos 

 before filtration. 



In making the choice of a precipitant for the ferricyanogen 

 ion with a view to subsequent testing for the sulphocyanogen 

 ion by the ferric salt, some reagent giving a colorless solution 

 was preferable. Salts of the elements zinc and cadmium meet 

 this condition and cadmium salts proved to be the more delicate. 

 Following the general method already mentioned, it was found 

 that - 0001 grm. of the ferricyanide could be readily detected 

 in from 5 cm3 to 10 cm3 of water acidified with acetic acid even 

 when 0*1 grm. of potassium sulphocyanide was present. The 

 cadmium ferricyanide presented the same difficulty in filtra- 

 tion that has been described in the case of the thorium ferro- 

 cyanide, and the difficulty was overcome in the same manner. 



The method as recommended is as follows: The solution to 

 be tested, preferably dilute and about 5 cm3 to 10 cm3 in volume, 

 is acidified faintly with acetic acid or hydrochloric acid and 

 treated with a soluble thorium salt to complete precipitation. 

 To the liquid and suspended thorium ferrocyanide some finely 

 shredded asbestos is added, the whole is agitated and thrown 

 on a filter and the precipitate washed with a little water. 



The presence of the ferrocyanide may be confirmed by de- 

 composing the washed precipitate with strong sodium hydrox- 

 ide on the filter, acidifying the clear filtrate with hydrochloric 

 acid and testing with ferric chloride. 



The filtrate from the thorium ferrocyanide is treated with a 

 soluble cadmium salt to complete precipitation of the cadmium 

 ferricyanide, which after the addition of the asbestos is fil- 

 tered and washed as previously described. The presence of the 

 ferricyanide may be confirmed by treating the cadmium ferri- 

 cyanide with sodium or potassium hydroxide, acidifying the 

 filtered solution and testing with a ferrous salt. 



The filtrate from the cadmium ferricyanide is acidified with 

 hydrochloric acid and treated with ferric chloride, which gives 

 the red ferric sulphocyanide. 



Am. Jour. Sci. — Fourth Series, Vol. XXIII, No. 138.— June, 1907. 

 31 



