309, 310] The Werner Schmidt Method 183 



Some analysts prefer to heat the tube in a water bath, but this 

 is a slow process, and as the only object of this method is to 

 obtain a rapid result with fair accuracy, it is best to proceed as 

 quickly as possible. 



When the liquid is quite free from clots it is cooled down, 

 and the tube filled up to the 50-c.c. mark with ether. The 

 tube is corked up, well shaken, and allowed to stand until the 

 ethereal layer has completely separated. 



Ten c.c. of this ethereal extract is measured off into a 

 weighed dish, evaporated to dryness, and weighed. The result, 

 after subtracting the weight of the dish, will be one-fifth of the 

 weight of fat in 10 c.c. of milk. Knowing the specific gravity 

 of the milk, it is easy to calculate the percentage of fat. 



Soxhlet's Areometric Method 



309. Apparatus. — The apparatus, which is shown in 

 fig. 46, consists of a bottle in which the solution of the fat takes 

 place, and a tube surrounded by a water jacket and enclosing a 

 delicate hydrometer giving specific gravities from 743 to 766. 

 Attached to the hydrometer is a thermometer. The bottle 

 may be connected with the water-jacketed tube by inserting an 

 india-rubber stopper through which pass two tubes arranged 

 as for a wash bottle, the delivery tube being attached to the 

 apparatus whilst the blowing tube has an india-rubber blower 

 fixed to it. This apparatus is complete for one determination. 

 Should a large number be required in rapid succession, a large 

 number of bottles will be required. 



310. The Operation. — Measure out 200 c.c. of milk into 

 one of the bottles; add 10 c.c. of caustic potash solution 

 (the solution used for expelling ammonia after heating with 

 H 2 S0 4 in the acid process of nitrogen estimation, paragraph 

 91, may be used) and 60 c.c. of ether. The ether must be 



