542 MODE OF SEPARATING THE CONSTITUENTS OF MILK. 



§ 4. O/* the mode of separating and estimating the several constituents 



of milk. 



1°. If a weighed quantity of milk be allowed to stand for a sufficient 

 length of time, the cream will rise to the top, and may be easily skim- 

 med off. If this creatn be gently heated the butter in an oily form will 

 collect upon the surface, and when cold may be separated from the 

 water beneath, and its weight determined. 



2°. If the skimmed milk be gently warmed, and a little vinegar or 

 rennet then added to it, the curd will separate, and may be collected in a 

 cloth, pressed, dried, and weighed. 



3*^. If a second equal portion of the milk be weighed and then evap- 

 orated to dryness by a gentle heat and again weighed, the loss will be 

 the (juantity of water which the milk contained. 



4^^. If now the dried milk be burned in the air till all the combustible 

 matter disappears, and the residue be weighed, the quantity of inorganic 

 saline matter will be determined. 



5°. Supposing those processes to be performed with tolerable accuracy, 

 the difference between the sum of the weight of the water, butter, curd, 

 and ash, and the weight of the milk employed, will nearly represent 

 that of the sugar contained in the given quantity of milk. 



For many purposes a rude examination of milk after this mahner may 

 be sufficient, but where any thing like an accurate analysis is required, 

 more refined methods must be adopted. In such cases, the following 

 appears to be the best which has hitherto been recommended. [Haid- 

 len, Annal. der Chem. & Phar., xlv., p. 263.] 



a. The butter. — The weighed quantity of milk is mixed with one- 

 sixth of its weight of common unburnt gypsum previously reduced to a 

 very fine powder. The whole is then evaporated to dryness with fre- 

 quent stirring at the heat of boiling water (212° F.) A brittle mass is 

 obtained, which is reduced to fine powder. By digesting this powder in 

 ether, the whole of the butter is dissolved out, and by evaporating the 

 ether, may be obtained in a pure state and weighed. Or the powder 

 itself, after being treated with ether, may be dried and weighed. The 

 butter is then estimated by the loss. 



6. The sugar. — After the removal of the butter, alcohol is poured upon 

 the powder and digested with it. This takes up the sugar with a little 

 saline matter soluble in alcohol. By evaporating this solution and 

 weighing the dry residue, the quantity of sugar is determined. Or, as 

 before, the powder itself may be dried and weighed and the sugar esti- 

 mated by the loss. If we wish to estimate the small quantity of inor- 

 ganic saline matter which has been taken up along with the sugar, it 

 may be done by burning the latter in the air, and weighing the residue. 



c. The saline matter. — A second weighed portion of milk is now evap- 

 orated carefully to dryness and again weighed. The loss is the water. 

 The dried milk is then burned in the air. The weight of the incombus- 

 tible ash indicates the proportion of inorganic saline matter contained in 

 the milk. 



d. The casein. — The weight of the butter, sugar, saline matter and 

 water being thus known and added together, the deficiency is the weight 

 of the casein. 



