1 82 The Analysis of Dairy Produce [307, 308 



apparatus (fig. 38), and extract with ether for 1^ hour. 

 Transfer the fat to a beaker, and weigh exactly as described in 

 paragraph 142. 



307. Rapid Methods. — Of late years several forms of 

 apparatus have been introduced which estimate the amount of 

 fat in milk both rapidly and accurately. These may be divided 

 into three classes, ' the gravimetric,' the ' areometric,' and the 

 1 centrifugal.' In the areometric and gravimetric methods a 

 certain quantity of ether is mixed with a certain quantity of 

 milk, and then allowed to separate. The percentage of fat is 

 deduced either from the specific gravity of the ether, or by 

 evaporating an aliquot portion of the ether and weighing. In 

 the centrifugal methods the milk is first acted upon by some 

 reagent which will dissolve the casein, then the fat is separated 

 by centrifugal force. One form of each of these three methods 

 is given below. 



The Werner Schmidt Method 



In this method the casein, &c, are dissolved by boiling with 

 hydrochloric acid. This leaves a brown solution from which 

 the fat may be easily extracted by shaking with ether. The 

 percentage of fat in the ether is estimated by evaporating a 

 portion and weighing the dry residue. 



308. The Process. — A Werner Schmidt tube is a stoppered 

 test tube of 70 or 80 c.c. capacity ; it has a mark to indicate 

 when it contains 10 c.c. of liquid and another to indicate 20 c.c. 

 Above the 20-c.c. mark are accurate graduations for every 

 o*i c.c. up to 50 c.c. 



Ten c.c. of the well mixed milk is poured into this tube, 

 then 10 c.c. of strong hydrochloric acid is added. The 

 mixture is well shaken, then boiled for a few minutes over a 

 Bunsen. The liquid will then be clear but deep brown. 



