222 Browning and Porter — Qualitative Separation 



decomposition of the ferrocjanide when formed and upon the 

 application of strong hydrochloric acid to the separation of 

 gallinm and aluminium. 



It was found that when solutions containing about 0"1 grm. 

 of aluminium or beryllium were strongly acidified with hydro- 

 chloric acid and treated with potassium ferrocyanide no precip- 

 itation took place, while O'OOl grm. of gallium in the presence 

 of O'l grm. of aluminium was easily precipitated and detected 

 at once. Amounts of gallium as small as O'OOOl grm. could be 

 detected after the solution had been allowed to stand an hour 

 or so. These tests were generally made in a volume of liquid 

 from about 5^°^^ to 10^°"^, of which from one-quarter to one- 

 third was strong hydrochloric acid. 



With traces of zinc present, the use of potassium ferrocyan- 

 ide as the precipitant may lead to erroneous conclusions, because 

 zinc ferrocyanide is almost as readily precipitated as the gal- 

 lium. The presence of zinc maj- be avoided by the careful 

 application of the ammonium chloride and ammonium hydrox- 

 ide process. Should, however, traces of zinc remain, we have 

 found that they may be satisfactorily detected and removed by 

 treating a sodium hydroxide solution with hydrogen sulphide, 

 which removes the zinc without precipitating the gallium. 

 The filtrate, which must still be alkaline, is acidified, and free 

 hydrogen sulphide removed by boiling. The sulphur is oxi- 

 dized by hj'drogen dioxide in sodium hydroxide solution, and 

 the boiling is continued to remoye the excess of hydrogen diox- 

 ide. This solution is then acidified with hj-drochloric acid and 

 the usual ferrocyanide test may be made for gallium. Solu- 

 tions were prepared containing gallium and zinc and were 

 analyzed by the experimenter without knowledge of the con- 

 tent. The results follow : 



Issued Found 



Zn absent, Ga present 

 Zn present, Ga present 

 Zn present, Ga absent 

 Zn absent, Ga absent 

 Zn present, Ga absent 

 Zn present, Ga very faint 



indication 

 Zn present, Ga present 

 Zn present, Ga present 



The faint indication or tuto presence of Ga in experiment (6) 

 seemed to indicate a trace ot that element in the zinc. It is of 

 interest to note that this ind'cation was not obtained until the 

 solution had stood twenty minutes, while in experiment (8) the 



(1) 0-001 grm. Ga 



(2) 0-001 grm. Zn + 



(3) 0-001 grm. Zn 



(4) Distilled water 



(5) ^o: ^.m. Zn 

 ^6) 0-0-^ otiMn. Zn 



0-001 grm. Ga 



(7) 0-050 grm. Zn + 



(8) 0-050 -rir Zn + 



0-001 grm. Ga 

 0-0002 grm. Ga 



