THE ANALYSIS OF MILK 15 



of chlorine. [Note. A little of the chlorine, about o.oi 

 per cent., is lost on ignition of the total solids.] 



For the estimation of lime and phosphoric acid, it is 

 advisable to take another quantity of milk (10 c.c. or 

 25 c.c. being preferable) ; this is dried on the water- 

 bath, ignited, the ash dissolved in a little hydrochloric 

 acid, and the solution boiled; after cooling slightly, 

 ammonia is added drop by drop till a permanent tur- 

 bidity appears, and hydrochloric acid added in quantity 

 sufficient to remove this, excess being avoided. The 

 solution is brought just to the boiling-point, and a satu- 

 rated solution of ammonium oxalate added drop by 

 drop, so long as a precipitate appears ; the solution is 

 kept hot (in a water-oven) for at least two hours, and 

 filtered through a small ash-free filter ; the precipitate 

 is transferred to the filter, washed with hot water, and 

 the filter placed in a tared basin, and ignited over a small 

 flame ; when the filter-paper is all burnt away, the 

 precipitate is moistened with a solution of ammonium 

 carbonate, dried, and very gently ignited. The pre- 

 cipitate, now converted into calcium carbonate, is 

 weighed, and the weight of lime found by multiplying 

 by 0.56 ; it is usually slightly grey, and contains traces 

 of iron, which are small enough to be neglected. 



To the filtrate is added 5 or 10 c.c. of magnesia 

 mixture (see Appendix), and about one-tenth its volume 

 of strong ammonia ; and after stirring well the liquid 

 is allowed to stand at least 12 hours ; the precipitate 

 is washed by decantation with dilute ammonia, 

 transferred to a filter, and the washing completed ; 

 the filter is placed in a weighed basin, and ignited 

 at first gently, and finally very strongly till white ; 

 the residue of magnesium pyrophosphate is weighed, 

 and the amount of phosphoric acid (as P 2 5 ) found 

 by multiplying by 0.6396. 



For the determination of other mineral constituents, 

 works on mineral analysis should be consulted. 



The Estimation of Acidity. Place 10 c.c. of 

 milk in a white porcelain basin (Fig. 12), add i c.c. of 



