METHODS OF ANALYSING IT. 345 



then extracted with ether, alcohol, and water. In my opinion 

 Haidlen's method (see vol. i., p. 383) is in many respects pre- 

 ferable to this, for the treatment of milk with definite quantities of 

 sulphate of lime presents great advantages for evaporating and 

 drying the fluid, and for determining the quantity of fat, indepen- 

 dently of the circumstance that the casein is insoluble in all 

 menstrua. Milk which has been treated with chloride of calcium, 

 a solution of sulphate of lime, or, according to Haidlen's method, 

 with dried gypsum, may easily be evaporated without experiencing 

 any loss by the formation of vesicles of vapour ; while at the same 

 time the residue readily admits of being very perfectly dried, and 

 then easily pulverised. Ether readily and completely extracts the 

 fat, but alcohol does not remove any casein, either by boiling or 

 after the fluid has cooled. A different method must, however, be 

 adopted for the determination of the solid residue, the salts, and 

 the aqueous extract. The best mode of proceeding is to evaporate 

 from 1 to 3 grammes of milk in a flat platinum basin, either in a 

 vacuum or in a water-bath, and then to dry it in an air-bath 

 at + 120, or in a vacuum with the aid of a small sand-bath heated 

 to 120. The ash is best determined when a portion of well-dried 

 residue is burnt in a platinum crucible with the co-operation of 

 oxygen. Scherer's method is the only one by which the aqueous 

 extract can be determined with any degree of accuracy. 



We would refer to the observations already made (at p. 297 of 

 vol. i.), for the method of obtaining a quantitative determination 

 of the milk-sugar ; simply remarking here, that acid milk must be 

 neutralised before its evaporation, in order to obtain the milk- 

 sugar in a crystallised state. 



Dumas* observes that the milk-globules remain upon the 

 filter when the milk has been treated with a concentrated solution 

 of chloride of sodium. I have not been perfectly successful in 

 this experiment, even when I have used freshly drawn milk. 



Attempts have been made to invent instruments and methods 

 for determining with promptness the goodness of the milk, in 

 order to detect some of the numerous modes of adulterating cows 5 

 milk usually practised in large towns. These instruments, which 

 are termed yalactoscopes and galactomelers, are designed to furnish 

 an average determination of the quantity of fat contained in the 

 milk, since the goodness of this fluid for ordinary purposes is 

 estimated according to the amount of fat which it contains. The 

 best known of these instruments is the galactoscope invented 

 * Arch. gen. de M^d. Vol. suppl. 1846, p. 180. , 



