APPENDIX 633 



canted into a filter, and washed twice by decantation. The precipitate in 

 the beaker is then dissolved with a few drops of hydrochloric acid, a 

 little water added, and the calcium reprecipitated, boiling hot, by adding 

 ammonium hydroxid to slight alkalinity. A little ammonium oxalate 

 is added, the solution allowed to stand as before, and filtered through 

 the same filter; washed free from chlorids with hot water, the filter 

 burned and the precipitate ignited in a blast until it ceases to lose weight, 

 and weighed as calcium oxid (CaO). 



Calcium may be determined from the filtrate of the iron and aluminum 

 precipitates in the phosphorus determination. More care should be 

 taken, however, to wash the iron and aluminum precipitates free from 

 chlorids than is necessary when phosphorus alone is to be determined. 

 This filtrate must be run to dryness, and the silica dehydrated, then the 

 procedure continued as given above. 



Magnesium. The filtrate from the calcium determination is concen- 

 trated to about 50 cc. Then i g. ammonium persulfate is added, and 

 the solution boiled for 3 minutes to precipitate manganese. After fil- 

 tering the filtrate and washings are evaporated to dryness on the water 

 bath and ammonium salts expelled by careful heating. The residue is 

 taken up with 20 to 25 cc. hot water and about 5 cc. hydrochloric acid. 

 After it has stood until all that will has gone into solution, it is made 

 slightly ammoniacal and heated on the steam bath (or allowed to stand 

 over night), filtered, washed with distilled water, and the filtrate and 

 washings evaporated on the water bath to about 50 cc. If, as is 

 sometimes the case, a precipitate forms on standing, this must be 

 filtered out, washed, and the filtrate again evaporated to about 50 cc. 

 It is then made acid and enough acid sodium phosphate added to 

 precipitate all of the magnesium. While it is vigorously stirred, care 

 being taken not to strike or rub the sides of the beaker, enough 

 ammonia is slowly added to make it distinctly alkaline. It is then 

 allowed to stand half an hour, 10 cc. of strong ammonia slowly added 

 while it is again stirred vigorously, covered closely to reduce escape of 

 ammonia, and let stand for 12 hours. The precipitate is then filtered 

 and washed free from chlorids, using 2^ per cent ammonia water, the 

 filter dried, burned at first at a moderate heat, then ignited intensely 

 in the blast, and weighed as magnesium pyrophosphate (Mg 2 P 2 O7). 



