224 Broioning and Porter — Gallium. 



- An investigation was then made of the effect of nitrates in 

 general on ferrocyanides. It was found that when one drop 

 of potassium ferrocyanide is treated with 0*4 grm. of ammo- 

 nium nitrate in the presence of 6^"^ of 1 : 2 hydrochloric acid, 

 it is oxidized completely to the ferricyanide within two min- 

 utes, as may be shown by the use of a ferric salt and a ferrous 

 salt. If 0'2 grm. of ammonium nitrate is used under the same 

 conditions, the ferrocyanide is broken up in less than an hour, 

 while if only 0*1 grm. of ammonium nitrate is used a longer 

 time is required, but complete oxidation finally takes place. 

 Other experiments showed that 0*0001 grm. of gallium cannot be 

 precipitated as the. ferrocyanide in 5^"^ of dilute hydrochloric 

 acid in the presence of 3 drops of dilute nitric acid, whereas it 

 is readily precipitated in the absence of it. It was further 

 found that if O'OOOl grm. of gallium is precipitated and 1^""" 

 of dilute nitric acid is added, the precipitate is decomposed and 

 dissolved within forty-five minutes. It is thus seen that in 

 detecting gallium by the ferrocyanide method care must be 

 taken to have no nitrates or nitric acid present, and that these 

 may be successfully removed by evaporation with hydrochloric 

 acid. 



June, 1917. 



