225 



A New Method fur the Qualitative Detection op ('hlorides in 

 THE Presence of IjRomides and Iodides. 



By Frank C. Mathers aad Ika E. Lee. 



Mcisi of the sflu'ines ('(ir the separatinn nf i liln-ides frdiii Ijroiuides and 

 iddides (lepend upon one of two i^encra' luctlK.ds. 



I. Most of the (lUiilitative manna Is direct the treatment of tlie sohi- 

 tion tif the haloi^ens with an oxidizinu' a^'ent (if su<-li a strength that iodine 

 and bromine lint not chlorine aiv set free. The liberated bromine and 

 iodine may be removed from the solution by bdilins:, or by a current of air 

 or by sliakin.i; out witii sonic solvent sudi as carbon liisulphide. Experi- 

 ments conducted by lUlAanced students in this laboratory with this general 

 method have ])een fairly successful, excei>t that some chlorine is always 

 set free if the reaction is carried far enouiih to remove all of the bromine. 

 This method was fouml to be a failure in the hands of inexiierienced stud- 

 ents in (lualitative anal.vsis, perhaps on acc(nint of the necessity of excep- 

 tionally close adherence to directions. 



1'. The other general scheme for the se](aratiou depends upon the fact 

 tliat silver chloride is soluble and silver i<nlide and bromide are insoluble in 

 ammonium carbonate solution. After filtration from the luidissolved silver 

 bromide and iodide, the silver chloride is reprecipitated by neutralizinii' 

 the ammonium carbonate with nitric acid. However, silver bromide, Ks 

 soluble enough to produce a strong turbidity njion additi(>n of the nitric 

 acid. This is very confusing to the students. In addition to this trouble, 

 the method is so very delicate that traces of chlorides which are present 

 in most chemical reagents as im]iuritics. will give a distinct tni'bidity so 

 that the student is forced to decide from the (luantity of precipitate wheth- 

 er chlorides have been added or not. 



In the scheme described in this pajier. the residue of silver chloride, 

 bromide and iodide is treated with dilute ammoninni hydroxide or cor- 

 bonate, and the filtrate is treated with annnonium chloride, which will 

 produce a turbidity or precipitate if silver chloride is present. This precip- 

 itation is caused by the action of the ion CI from the ammonium chloride 

 upon the common ion CI from the silver chloiide. The annnonium chloride 



