322 Browning and Howe — Detection of Sulphides, etc. 



were made for the sulphite and thiosulphate, after removing 

 a considerable amount of the sulphide in the manner described, 

 and of the sulphate by acidifying and adding barium chloride. 

 The method as we have modified it may be summarized as 

 follows : To about 0"l grm of the substance to be analyzed dis- 

 solved in 10 cm3 of water or more, add sodium, potassium or 

 ammonium hydroxide to distinct but faintly alkaline reaction. 

 The solution should be neutral or alkaline rather than. even 

 faintly acid, owing to the readiness with which sulphur sepa- 

 rates. To the alkaline solution add zinc acetate in distinct 

 excess and filter. The precipitate may be tested for hydrogen 

 sulphide, on acidifying, in the usual manner. To the filtrate 

 add acetic acid, a few drops in excess of the amount necessary 

 to neutralize, and barium chloride, and filter through a double 

 filter. To the filtrate add iodine until the solution takes on a 

 permanent yellow tinge, and then bleach with stannous chlor- 

 ide, best after adding a few drops of hydrochloric, acid to 

 prevent the possible precipitation of a basic salt of tin. A 

 precipitate at this point indicates the sulphite. Filter, add 

 bromine water in faint excess to the filtrate, bleaching again 

 with stannous chloride. A precipitate on adding bromine 

 indicates a thiosulphate originally present. 



