LIME METHOD OF IMMENDORFF 229 



heating of the crucible, the remaining alcohol burns off ; and when 

 the paper has been completely destroyed, the heat is raised to the 

 full power of a bunsen for about five minutes. After cooling in 

 a desiccator the crucible containing the calcium sulfate is weighed. 

 The filtration may also be accomplished on asbestos felt. 



201. The Ammonium Oxalate Method. This method has 

 been extensively used in this country in commercial work, and is 

 carried out as described by Wyatt. 87 The total filtrates from the 

 iron and alumina precipitates, secured as described in paragraph 

 196, are well mixed and concentrated to a volume of about 100 

 cubic centimeters. There are added about 20 cubic centimeters 

 of a saturated solution of ammonium oxalate, and, after stirring, 

 the mixture is allowed to cool and remain at rest for six hours. 

 The supernatant liquid is poured through a filter, the residue 

 washed three times by decantation with hot water and brought 

 upon the filter. The beaker and precipitate are washed at least 

 three times. The precipitate is dried and ignited at low redness 

 for 10 minutes. The temperature is then raised by a blast and 

 the ignition continued for five minutes longer, or until the lime 

 is obtained as oxid. The precipitate is likely to contain some 

 magnesia. The magnesia is estimated in the filtrates from the 

 lime determination by first mixing them and concentrating to 

 loo cubic centimeters, which, after cooling, are made strongly 

 alkaline with ammonia. After allowing to stand for 12 hours, 

 the ammonium magnesium phosphate is collected and reduced 

 to magnesium pyrophosphate by the usual processes. If one 

 gram of the original material has been used, the pyrophosphate 

 obtained, multiplied by 0.36, will give the weight of magnesia 

 contained therein. 



202. Lime Method of Immendorff. The tedious processes 

 required to determine the lime in the presence of iron, alumina, 

 and large quantities of phosphoric acid are well known to ana- 

 lysts. Immendorff has published a method, accompanied by ex- 

 perimental data, based on the comparative insolubility of cal- 

 cium oxalate in a very dilute solution of hydrochloric acid. He 

 has shown in the data given that the lime is all precipitated in 

 the conditions named and that the precipitate, when properly pre- 



87 Phosphates of America, 4th Edition, 1892 : 153. 



