MINERAL CONSTITUENTS 77 



and the small precipitate of calcium phosphate collected, ignited, 

 and weighed. Its weight is subtracted from the previous 

 weight, and the difference gives the weight of calcium carbonate, 

 which, multiplied by 0.4, gives the calcium, or by 0.56, the lime 

 (CaO) contained in it; the weight of calcium phosphate mul- 

 tiplied by 0.3871 gives the calcium (Ca), or by 0.5419, the lime 

 (CaO) contained in it. The total calcium or lime is the sum of 

 the two. 



The filtrate is made strongly ammoniacal by the addition of 

 strong ammonia (0.880) and allowed to stand twenty-four hours. 

 The precipitated magnesium ammonium phosphate is filtered 

 off, washed with dilute ammonia, ignited, and the magnesium 

 pyrophosphate (Mg2?207) weighed. Its weight multiplied 

 by 0.2162 will give the magnesium (Mg), or by 0.3604, the 

 magnesia (MgO) contained in it. 



To the filtrate from this, magnesia mixture is added, and 

 the precipitate, after standing twenty-four hours, is treated 

 as above. From the total weight of the two quantities of mag- 

 nesium pyrophosphate, the phosphoric anhydride is calculated 

 by multiplying by 0.6396; to this is added the phosphoric anhy- 

 dride in the calcium phosphate, calculated by multiplying 

 the weight by 0.4581. This method takes no account of the 

 traces of iron present, which are precipitated with the calcium 

 phosphate and the magnesium-ammonium phosphate. If 

 desired, this may be estimated by dissolving the precipitate of 

 calcium phosphate and the first magnesium-ammonium phos- 

 phate precipitate in dilute hydrochloric acid, and determining 

 the iron colorimetrically as thiocyanate. 



To estimate alkalies, another portion of milk is ignited as 

 before, and the total ash dissolved in dilute hydrochloric acid 

 and boiled; a few drops of barium chloride solution, containing 

 not more than 0.1 grm. of barium to 100 grms. of milk are 

 added, and the boiling continued for some minutes. After some 

 hours, the precipitate of barium sulphate is filtered off, washed, 

 ignited, and weighed; its weight multiplied by 0.3433, will 

 give the sulphuric anhydride (SOs) in the milk. If an excess 



