236 QUANTITATIVE ANALYSIS. 



solution obtained from the ash and containing all of the iron 

 as ferric salt a few cubic centimeters of sodium phosphate 

 solution, make alkaline with ammonia, and acidify with 

 acetic acid. The precipitate of ferric phosphate resulting is 

 collected on an ash-free filter, washed, dried, ignited (in a 

 porcelain crucible), and weighed. One hundred parts corre- 

 spond to 52.98 parts of Fe 2 3 or to 37.09 parts of Fe. 



Since by this method it makes no difference if the solution 

 still contains traces of organic matter, the evaporation of 

 the diluted sulphuric acid, ignition, and dissolving again in 

 sulphuric acid (see above) may be omitted. (In the titra- 

 tion with permanganate this procedure is also frequently 

 unnecessary). Frequently also all the iron passes so com- 

 pletely into the hydrochloric acid solution (especially in the 

 determination of iron in the organs, which is made in an 

 exactly analogous manner) that it is sufficient to treat the 

 ash remaining with a little hydrochloric acid, filter the 

 diluted solution, add it to the first hydrochloric acid extract, 

 and then precipitate the iron directly from the hydrochloric 

 acid solution. Hydrochloric acid solutions cannot, however, 

 be titrated with potassium permanganate solution. 



