90 MILK AND DAIRY PRODUCTS PART 



of Table VIII in the Appendix. The temperature at which the 

 reading is made must be exactly 17*5 C., for it is not easy to 

 apply a correction in this case. Samples of milk which have 

 been treated with preservatives of different sorts can be 

 examined by this method quite as well as fresh milk. 



The method, however, is only applicable to cow's milk ; that 

 of other animals gives quite false results. 



Where a refractometer is present this method is without 

 doubt the simplest that can be employed and is of the 

 greatest assistance where a large number of estimations of 

 milk sugar have to be made at the same time. 



VI. DETERMINATION OF THE ASH. 



About 25 g. of milk are weighed out into a platinum dish and 

 thoroughly dried on the water-bath. 1 The contents of the 

 dish are then carefully burnt, and the black residue repeatedly 

 extracted with warm water. In this way the mineral sub- 

 stances are separated from the carbon, and the latter can then 

 be ignited until all have disappeared. The water containing 

 the salts is then returned to the platinum dish and evaporated 

 to dry air. The ash which is left is ignited at a low red heat 

 until it becomes perfectly white, and it is then weighed. It is 

 necessary to follow exactly the method given above if concor- 

 dant results are to be obtained, for if the mass containing 

 carbon is heated very strongly whilst the mineral salts are still 

 present there is certain to be some loss. It is, indeed, difficult 

 to avoid a slight loss, for in the process of ignition the citrates 

 are decomposed, and the mono- and di-phosphates lose water 

 and pass into the meta- and pyro-phosphates. Vieth 2 has 

 shown that when the ash of milk is ignited at bright red heat 

 for thirty minutes, the chlorine is reduced from 0*09 per cent, 

 to 0-003 per cent. 



When the milk has been preserved with potassium bichromate 

 a separate determination of the preservative must be made. 

 This is done after the estimation of total ash, as given above, by 

 means of the following method. 3 Necessary reagents : 



1 Fleischmann recommends the addition of a few drops of acetic acid to 

 prevent a skin forming on the milk. 



2 Forschungen aufdem Gebiete der Viehhaltung, &c., Vol. XV, p. 332. 



3 " Arrete relatif aux methodes qui devront etre employees par les laboratoires 

 agrees pour 1'analyse des laits concentres ou laits desseches. " Journal Officiel du 

 9 Mars, 1907. 



