BROMINE IN SEA WATER. 83 



'2d Operation. — Conversion of the cuprous bromide into 

 zinc bromide. — This is accomplished by zinc with the addi- 

 tion of a little hydrochloric acid. The operation is an easy 

 one, and would seem to require no explanation. But for 

 the 3d operation, the titration, I require a small volume, say 

 25 c.c, in our case. A judicious economy of water and acid 

 is, therefore, imperative. The precipitate in the flask is di- 

 gested with about 100 c. c. of cold water, to which about 1 

 grm. of sulphuric acid has been added. The settled liquid 

 is decanted as before, the last portion over a very small 

 filter. Any iron which the cupric sulphate may have con- 

 tained is now reduced to a no longer appreciable amount, and 

 the sulphurous gas much reduced. But in order to destroy 

 the last trace of the latter, I add a few drops of sodium car- 

 bonate and spread the crystalline powder around the flask. 

 After one or two minutes enough oxychloride will be formed 

 to answer the purpose afterwards. Now I rinse the con- 

 tents of the flask into a porcelain dish, using only a few 

 cubic centimeters at one time; heat in a test-tube about 

 5 c. c. water, with J c.c. hydrochloric acid, and filter over 

 the small filter I had been using into the flask. A little 

 more water applied to filter and flask will clean both 

 sufi&ciently. The dish is heated on a water bath, and when 

 by smell I detect no sulphurous gas, I add one large amply 

 sufiicient piece of zinc. 



The white crystals will soon be replaced by copper and a 

 clear solution of cuprous chloride in hydrochloric acid. 

 The finished reduction I recognize by touching with the 

 point of a glass rod first the liquid and then a drop of sul- 

 phuretted hydrogen water spread on a porcelain plate. 

 Enough acid must be present to prevent the formation of 

 oxychloride of zinc. The contents of the dish, copper and 

 all, are filtered over a small filter, directly into a small 

 graduated cylinder, and ought not to give more than 10 or 

 15 c.c. filtrate. The copper is then fully sweetened into 

 another porcelain dish with about 25 c.c. of hot acidulated 



