II] SOILS 23 



in a desiccator and weigh as ferric oxid (Fe203), aluminium oxid (AUOs), and phos- 

 phorus pentoxid (P2O5). Transfer this residue to a flask, digest with several cc. 

 of sulphuric acid (1 to 4), and heat to accelerate solution. When solution is complete 

 reduce with zinc and determine the ferrous iron by titration with a standard per- 

 manganate solution, and calculate to ferric oxid; or, (2) In lieu of the above, evapo- 

 rate 50 or lOOcc.of A, underll, with the addition of 10 cc. of su phuric acid until all 

 hydrochloric acid is expelled, dilute with water, reduce with zinc and determine the 

 ferrous iron by titration with a standard permanganate solution and calculate to 

 ferric oxid. 



The weight of ferric oxid, plus that of the phosphorus pentoxid, determined 

 under 17 or 19, subtracted from the collective weight of ferric oxid, aluminium 

 oxid, and phosphorus pentoxid, gives the weight of the aluminium oxid. 



1 4 MANGANESE.— OFFICIAL. 



Concentrate B, under 13, to about 50 cc, cool, add bromin water until the solution 

 is colored, make alkaline with ammonium hydroxid, and heat to boiling in a covered 

 beaker; cool, and repeat the addition of bromin water, of ammonium hydroxid and 

 boil again. If a precipitate is obtained, slightly acidify the solution with acetic 

 acid, filter immediately, and wash with hot water. Dry the precipitate, ignite and 

 weigh as manganomanganic oxid (MnsO^). Designate the filtrate, or if there is no 

 precipitate, the original solution, as C. 



1 5 CALCIUM.— OFFICIAL. 



Concentrate C, under 14, to about 50 cc, make slightly alkaline with ammonium 

 hydroxid, and add, while still hot, ammonium oxalate solution, drop by drop, slightly 

 in excess of complete precipitation, to convert the magnesium also into oxalate. 

 Heat to boiling, allow the precipitate to settle completely, decant the clear solution 

 on a filter, pour 1.5-20 cc. of hot w^ater on the precipitate, and again decant the clear 

 solution on the filter. Dissolve the precipitate in the beaker with a few drops of 

 hj'drochloric acid, add a little water, repeat the precipitation as above, and filter 

 through the same filter; transfer the precipitate to the filter and wash free from chlo- 

 rin with hot water; dry, ignite the precipitate over the blast lamp to constant weight, 

 and weigh as calcium oxid. Designate the filtrate and washings as D. 



1 6 MAGNESIUM.— OFFICIAL. 



Evaporate D, under 15, to dryness on the water bath and heat carefully to expel 

 ammonium salts. Treat the residue with 20-25 cc. of hot water and about 5 cc. of 

 hydrochloric acid, filter and wash. Concentrate to about 50 cc, cool, and add suffi- 

 cient disodium hydrogen phosphate solution to precipitate the magnesium; then 

 add gradually ammonium hydroxid, with constant stirring, until the solution is 

 distinctly alkaline. Determine if the precipitation is complete by the addition of 

 more of the disodium hydrogen phosphate solution. After 30 minutes, add gradually 

 10 cc. of strong ammonium hydroxid, cover to prevent the escape of ammonia, and 

 let stand in the cold. Filter after 12 hours, wash the precipitate free from chlorin, 

 using dilute ammonium hvdroxid [I, 4 (d)], dry the filter and precipitate and trans- 

 fer the latter to a weighed porcelain crucible. Ignite the filter separately and add 

 its ash to the precipitate in the crucible. Burn at first at a moderate heat, then 

 ignite to whiteness or to a grayish white, weigh as magnesium pyrophosphate 

 (MgoPeO?) and calculate to magnesium oxid (MgO). 



