225 



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

 THE Presence op I^romides and [odides. 



r>v Fka?\'k C. Mathers and Ika E. Lee. 



Most of the schemes i'm- the separation of chla-ides fi-din hi'mnides and 

 iodides depend npon one of twd Lrenerai nietlicds. 



1. Most of tile (lualitntive niaiinals dirert the treatment of the soln- 

 tion of tlie hahigens witli an oxidizini;- agent of sncli a strengtli that iodine 

 and lu'oniine hnt not elilorine are set free. The liberated bromine and 

 iodine may lie renio\ed from the sohition by Imiling, or by a current of air 

 iir l»y sliaUing out with some solvent sndi as carbon bisnlpliide. Experi- 

 ments ((inducted by advanced students in this labdratory witli tliis general 

 method have been faii'ly succ<'ssful. excejit lliat s(ime chliu-ine is always 

 set free if the reactidu is carried far eudutih (d remove all of the bromine. 

 This method was fdiuid to be a failure in the hands of inexperienced stud- 

 ents in (|ualitative analysis, jierhaps (in account of the necessity of excep- 

 tidually close adherence to directions. 



2. The other general scheme for the separation depends upon the fact 

 that silver chloride is soluble and silver iodidi^ and bromide are insoluble in 

 ammonium carbonate sdlution. After filtration from the undissolved silver 

 bromide and iodide, the silver chloride is reprecipitated by neutralizing 

 the ammonium carbonate with nitric acid. However, silver Iiromide, la 

 soluble enough to produce a strong turbidity upon additidu df the nitric 

 acid. This is very Cdufusing td 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 imiiurities, will give a distinct tiu-bidity so 

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

 er chlorides have been added or not. 



In the scheme described in this paiier, the residue of silver chloride, 

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

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

 produce a turbidity or precipitate if silver chlorhle 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 chloride. The anunonium chloride 



