Separation and Estimation of Phosphoric Acid. 181 







Art. XIII. — On the Quantitative Separation and Estimation of 



Phosphoric Acid; by H. Rosk.* 



The second No. of the Annalen der Physik and Chemie for 

 1849, contains an elaborate and most valuable memoir by H. Rose 

 on the quantitative separation and estimation of phosphoric acid. 

 As this memoir furnishes the complete solution of one of the 

 most difficult problems in analytical chemistry, we here olfer a 

 brief abstract of its contents. Some of the facts in relation to 

 the action of the alkaline carbonates upon the phosphates of 

 lime and magnesia will of course be familiar to many readers ; 

 still it may not be improper to mention them as the whole sub- 

 ject is discussed in the original memoir. 



1. Phosphoric acid existing in a solution uncombined with 

 bases is best determined by adding a weighed portion of oxyd of 

 lead, (freshly ignited,) evaporating to dryness, and igniting. JVo 

 bases must be present and no acids which cannot be completely 

 expelled from the oxyd of lead by heat. The application of this 

 method is independent of the particular modification in which 

 the phosphoric acid may exist. 



2. In determining phosphoric acid by means of magnesia and 

 ammonia, it is indispensable that the acid be present in the G\ 

 modification. After adding sulphate of magnesia, ammonia and 

 chlorid of ammonium, the solution may be gently warmed (as 

 nigh as 30° C.) and after several hours filtered. The resulting 

 phosphate of ammonia and magnesia is to be washed out with 

 ammoniacal water in the manner recommended by Presenilis. A 

 solution of carbonate of ammonia cannot be substituted for the 

 pure alkali in this process. 



3. Phosphoric acid cannot be perfectly separated from peroxyd 

 of iron by means of sulphuret of ammonium, as has been hereto- 

 fore supposed. The resulting sulphuret of iron contains indeed 

 no traces of phosphoric acid, but on the other hand the precipita- 

 ted phosphate of magnesia and ammonia is not free from oxyd 

 of iron. t 



4. Berthier's method of separating phosphoric acid from basic 

 °xyds (by adding a solution of peroxyd of iron and afterward am- 

 monia) does not give satisfactory results in quantitative analyses. 



5. Von KobelPs modification of Berthier's method (by means 

 of carbonate of baryta and solution of peroxyd of iron) gives good 

 results in cases where the basic oxyds are not precipitated from 

 their cold solutions by the carbonate of baryta alone. 



* Condensed for this Journal by Dr. Wolcott Gibbs. 



