180 MILK 



"25 to 50 grams of milk are evaporated and the solids ignited 

 over barely perceptible red heat until thoroughly charred, otherwise 

 alkaline chlorids are lost. The ash is extracted with hot water 

 and filtered. The residue on the filter is ignited at red heat until 

 white. This gives the insoluble ash. The filtrate is evaporated 

 and cautiously ignited at low temperature and the soluble ash 

 obtained. This method gives 0.02 per cent, higher results than 

 ignition of the total residue. To examine the ash further two 

 parts are kept separate. One part is titrated with N. 0.1 acid 

 with methyl orange as indicator for alkalinity and with standard 

 silver nitrate solution for chlorin, with potassium chromate as 

 indicator. 



"The insoluble part is dissolved in a slight excess of hydro- 

 chloric acid, the solution nearly neutralized with ammonia, and 

 heated to boiling. A cold saturated solution of ammonium ox- 

 alate is dropped in slowly until no more precipitate forms. This 

 should stand for at least two hours. Then the precipitate is 

 filtered off, washed, and ignited at low temperature. The ignited 

 precipitate may be moistened with ammonium carbonate solution 

 and re-ignited at low temperature. After weighing, the residue 

 is dissolved in dilute hydrochloric acid, keeping the bulk smajl; 

 ammonia is added to an alkaline reaction. The small precipitate 

 of calcium phosphate is collected, ignited, and weighed. The 

 weight is subtracted from the previous weight and the difference 

 gives calcium carbonate, which, multiplied by 0.4, gives the cal- 

 cium, or by 0.56, the lime. The weight of the calcium phosphate 

 multiplied by 0.3871 gives the calcium; by 0.5419, the lime. The 

 total calcium or lime is the sum of the two. 



"The filtrate is made strongly ammoniacal with 0.880 ammonia 

 and allowed to stand for twenty-four hours. The precipitated 

 magnesium-ammonium phosphate is filtered off, washed with 

 dilute ammonia, ignited, and the magnesium pyrophosphate 

 weighed. The weight multiplied by 0.21622 gives the magnesium, 

 and by 0.36036, the magnesia obtained. To the filtrate from this 

 magnesia mixture is added. The precipitated magnesium-am- 

 monium phosphate is filtered off after twenty-four hours and treated 

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

 nesium pyrophosphate the phosphoric anhydrid is calculated by 

 multiplying by 0.63964. To this is added the phosphoric anhydrid 

 in the calcium phosphate, calculated by multiplying the weight 

 by 0.4581. 



"No account of traces of iron is taken in this method. The 

 iron is precipitated with the calcium phosphate and the magnesium- 

 ammonium phosphate. If the iron is to be estimated the precipi- 

 tate of calcium phosphate and the first magnesium-ammonium 



