48 UNIVERSITY OF COLORADO 



1 large wide-mouthed bottle, white glass. 



1 rubber stopper with 4 holes, to fit same. 



1 50 cc. burette for hyposulphite solution. 



1 small pipette with stopcock for NaN0 2 , KI solution. 



1 small pipette with stopcock for H 2 S0 4 solution. 



1 350 cc. flask. 



Beakers, glass tubing, rubber tubing etc. 



Solutions. 



ZnS0 4 ,7H 2 0— 200 grams made up to 1 litre; 1 cc. soln.=.2 



grams ZnS0 4 ,7H 2 0. 

 Phenolphthalein. 



Na 2 S 2 3 — 7.75 grams per litre of water. 

 Bromine water. 



KI and sodic nitrite solution \ tt T 2 9 " n ° u 



KI and starch 



H 2 100 cc 



The method consists in: 



First— Adding KOH. 



Second— Adding ZnS0 4 .7H 2 0. 



Third — Determining hyposulphite required by Thresh's 



method with clear solution decanted from precipitates 



formed in the closed bottle. 

 Fourth — Qualitative tests for nitrites. 

 Fifth — Correction for nitrites and re-agents used. 



The Winchester quart and the 16-oz. bottle are filled with the 

 solution to be tested; the contents of the latter to be used for pre- 

 liminary work, and the former for the actual analysis. 



Take 100 cc. from the small bottle, add a few drops of phenol- 

 phthalein and run in the 20$ solution of ZnS0 4 until the alkaline 

 action has disappeared, which is seen at once by the characteristic 

 magenta color having vanished. It is advisable to filter the solu- 

 tion after the first disappearance of the pink coloration, as the ppt. 

 carries down the coloring matter. The amount required for the 

 Winchester quart, the contents of which are known, can then be 

 calculated. 



Add 5 or 6 grams of solid KOH to the Winchester quart, and, 

 when dissolved, add the required amount of solid ZnS0 4 .7H 2 0, 

 taking care not to allow any air to enter the solution. Replace 



