23-25] Estimation of Iron 21 



30 c.c. of hot water, using a few drops of dilute H 2 S0 4 to clear 

 the solution. The water must be poured down the sides of 

 the beaker to avoid all risk of splashing. 



23. Precipitation.— Raise the liquid to boiling-point 

 over a Bunsen burner, and add gradually 5 c.c. of strong nitric 

 acid. The liquid, which has hitherto been only just coloured, 

 will now acquire a deep-yellow tint from the oxidation of the 

 ferrous to a ferric salt. After it has boiled for a few seconds 

 remove it from the burner, and add dilute ammonia (3 of 

 distilled water to 1 of strong ammonia) cautiously. Stir with 

 a glass rod. Place a very small piece of litmus paper in the 

 beaker. Continue adding ammonia until the litmus paper 

 shows a distinctly alkaline reaction. A flocculent precipitate 

 of ferric hydrate will be thrown down. Cover the beaker with 

 a clock glass, replace it over a Bunsen flame, and allow it 

 to boil for about a minute. Turn out the light, and allow the 

 precipitate to settle. 



It is very convenient to have a small wash bottle of about 

 8 oz. capacity containing ammonia, the jet of liquid being 

 much preferable to the unmanageable stream which comes from 

 the mouth of a bottle. The special form of wash bottle de- 

 scribed in paragraph 14 is, however, necessary. The ordinary 

 form would often fill the operator's mouth with ammonia fumes. 



24. Filtration and Washing. — Whilst the precipitate is 

 settling, fit a 9-cm. filter paper into a clean glass funnel, and 

 moisten it with hot water. When the precipitate has settled 

 smear the outside of the lip of the beaker with the smallest 

 possible quantity of lard or vaseline, and pour the clear liquid 

 down a clean glass rod into the filter paper. Wash the pre- 

 cipitate by decantation exactly as directed in paragraph 12 (d). 



25. Drying, Igniting, and Weighing.— Cover the 

 top of the funnel with a piece of filter paper, and dry it in the 

 oven described in paragraph 16. Whilst it is drying clean a 



