1328 Journal of Applied Microscopy 



VII. With Primary Sodium Carbonate or Ammonium Carbonate. 



The latter reagent gives much better results, but even at its best the reaction 

 yields unsatisfactory crystals. 



Neutral, very dilute solutions are necessary in order that recognizable crystals 

 shall be obtained. The sodium salt tends to produce minute, spider-like 

 aggregates and spherulites. 



Ammonium carbonate yields tiny spindle-shaped crystallites, dumb-bells, and 

 irregular masses. 



The test is not applicable in the presence of Ca, Sr, Mg, Li, etc. 



SEPARATION OF THE CALCIUM GROUP. 



Brief outlines of the methods for the separation and identification of calcium, 

 strontium, and barium have already been given in the discussion of the various 

 tests for these elements. There remains, therefore, only the necessity of sum- 

 marizing the various processes. 



To separate this group from other elements, three reagents can be employed : 

 /, Ammonium Carbonate ; II, Oxalic Acid ; III, Sulphuric Acid. For conven- 

 ience each of these reagents will be discussed separately and in turn. 



/. Ammonium Carbonate in Ammoniacal Solution. 



In addition to Ca, Sr, and Ba ; there can also be precipitated a number of 

 other elements and compounds. Chief among these should be mentioned, rare 

 earths, Mn, Cr, Al, Fc, Pb, Magnesium group, phosphates, borates, arsenates, 

 molybdates, oxalates, tartrates, etc. 



Inasmuch as the tests for the elements other than those of Group I and the 

 Calcium group have not yet been described, it is not deemed expedient at this 

 point to enter into a discussion of the methods for dealing with complicated 

 mixtures. 



The clear liquid is drawn off, or otherwise separated from the precipitate 

 produced by the reagent. The precipitate is washed, and dissolved in hydro- 

 chloric acid. 



Test one portion of the hydrochloric acid solution with sulphuric acid for Ca, 

 if an amorphous or granular precipitate results, Sr or Ba (or Pb^ is present, or 

 the substance may contain both. 



Test a second portion with ammonium fluosilicate for Ba. 



If no Ba is found, test for Sr with ammonium dichromate and ammonium 

 hydroxide. 



If Ba is present, precipitate this element with dichromate in acid solution, 

 Draw off and test for Sr with ammonium hydroxide. 



//. Oxalic Acid. 



Three modifications can be satisfactorily employed, the choice being gov- 

 erned by the nature of the material. 



a. Precipitation with oxalic acid in nitric acid solution. 



b. Precipitation with oxalic acid in the presence of ferric chloride. 



c. Precipitation with oxalic acid in the presence of stannic chloride. 



