i MILK 95 



with caustic potash, and the soap which forms is decomposed with 

 dilute HNO 3 , and the liquid filtered off. By boiling the filtrate 

 and then heating it on the water-bath it is brought to dryness, 

 and then 10 c.c. of concentrated HNO 3 are added. Powdered 

 potassium permanganate is added to the warm liquid until the 

 pink colour persists for a few moments. Afterwards the man- 

 ganese oxide which forms is dissolved by the addition of a few 

 drops of a 10 per cent, solution of sodium nitrite. The solution 

 is then boiled to free it of nitrous fumes, and the phosphoric 

 acid determined in the usual way with ammonium molybdate 

 solution. After at least twelve hours, the precipitate is filtered 

 off, dissolved in the smallest possible quantity of NH 4 OH, and 

 precipitated with magnesia mixture, and the pyrophosphate 

 weighed in the usual way. The weight of the magnesium 

 pyrophosphate multiplied by T5495 gives the quantity of 

 glycero-phosphoric acid contained in the sample of milk. 



It has not yet been definitely decided which fatty acid is 

 combined with the glycero-phosphoric acid and the choline to 

 make the lecithin of milk. According to Stoklasa l it is stearic 

 acid (as in yolk of egg), whilst Burow 2 thinks oleic and butyric 

 acids are present. If the first view is accepted, then the 

 lecithin of milk would have the following formula : 



O CH0N 



.H.O, 



Multiplication of the amount of glycero-phosphoric acid by 

 4*69 gives the quantity of leci thine in the form of distearin 

 lecithin, whereas multiplication by 3*54 gives it as oleo-butyrin 

 lecithin. 



The most important part of the method described above is 

 the oxidation with potassium permanganate, and the more 

 complete this is, the exacter will the results be. Estimated in 

 this way the quantity of glycero-phosphoric acid in milk varies 

 between O'OIO and 0'020 g. per 100 c.c., and is dependent upon 

 the period of lactation. 



A more recent method, due to Nerking and Haensel, 3 gives 



1 Hoppe-Seyler's l Zeitschrift fur physiol. Chemie, 1897, Vol. XXIII, p. 343. 



2 Ibid., 1900, p. 495. 



3 Biochemische Zeitschrift, Vol. XIII, 1908, p. 348. 



