i MILK 39 



addition of the caustic potash solution and ether. To neutralise 

 the acetic acid, more caustic potash, 14 c.c., instead of 10 c.c., 

 must be used. 



After the fat-containing ether has separated, the water jacket 

 (A) is filled with water at a temperature of 16 to 18 C., and 

 the bottle is then connected as shown in Fig. 12. By carefully 

 pressing the rubber ball, the ether is forced into (B), care being 

 taken that only the clear liquid enters. The connection 

 between the bottle and the apparatus is then closed by a 

 pinchcock, and the small araeometer sunk into the ether. 

 When the araeometer floats freely in the liquid, the specific 

 gravity is read off on the scale. In order that the araeometer 

 may freely take up its proper position, the water jacket is 

 clamped horizontally to a retort stand, which can be carefully 

 regulated by a screw in the foot. The temperature must also 

 be read on the thermometer attached to the araeometer, and if 

 it is higher or lower than 17'5 C., a correction must be made 

 to get the true specific gravity of the ether solution. This 

 correction is the addition of one-tenth of a degree of the araeo- 

 meter scale for each one-tenth of a degree above 17'5 C., and a 

 corresponding deduction of one-tenth of a degree from the 

 specific gravity for each one-tenth of a degree below 17*5 C. 

 If, for example, the temperature of the ether is 16*9 C., and 

 the reading on the araeometer scale is 52'7, then the true 

 specific gravity is 52'1. 



When the determination has been made, the pinchcock is 

 opened and the ether flows back again into the bottle. The 

 tube (B) is then filled with ordinary ether, which is also allowed 

 to flow into the bottle. Finally, the rubber aspirator is fixed to 

 the lower end of the tube (V), and air forced through the 

 apparatus until it and the araeometer are perfectly clean and 

 dry. 



It is only possible to use the method as described above 

 when the milk contains at least 2'07 per cent, fat ; but Soxhlet 

 has worked out a modification which can be used for milk 

 poorer in fat, and also for separated milk and butter-milk. 

 This consists in adding a solution of soap to the milk, for then 

 the fat-containing ether separates more easily. The soap 

 solution is prepared by dissolving 15 g. of ordinary stearin 

 candle in a mixture of 25 c.c. alcohol and 10 c.c. of the above- 



