1 86 



MILK 



generally employed is a modification of the method originally 

 proposed by Gerber in 1892. In order to allow of the complete 

 separation of the fat, it is essential to dissolve the casein present 

 in the milk, and Gerber employed concentrated sulphuric acid for 

 this purpose. At a later date Lefifmann and Beam showed that 

 the addition of a small quantity of amyl alcohol 

 facilitates the separation of the fat in a pure clean 

 condition, and this method is the one which is at 

 present most largely employed in dairies, etc., 

 where a rapid method of fat estimation is required. 

 A Gerber's test-bottle is shown in Fig. 24, and 

 the centrifuge in Figs. 25 and 26. Some of the 

 latter have an arrangement for heating whilst in 

 motion, and may be driven by a strap, bevel- 

 gearing, water-motor, or other means. 



The method of carrying out the test is 

 as follows : — 



A test-bottle is placed with the open 

 end upwards, and 10 c.c. of pure sulphuric 

 acid of a density of 1-825 at 15° C. are 

 delivered into the bottle, either from a 

 pipette or from a special measurer (Fig. 26). 

 The sulphuric acid should not be 

 allowed to come into contact with the 

 neck of the bottle. Eleven c.c. of the 

 milk are then run carefully on to the 

 surface of the acid from a special pipette, 

 graduated for the volume, and i c.c. of 

 chemically pure amyl alcohol (boiling- 

 point 128° to 130° C.) is added from a 

 I c.c. pipette. The reagents should be 

 used in the order mentioned above. 

 The rubber stopper is fitted into the top of the 

 test-bottle, which is then wrapped in a cloth and 

 thoroughly shaken. A considerable rise in temperature 

 results during the mixing, and the test-bottle may 

 be either immediately placed in the centrifuge, or, in 



Fig. 24.— 



Gerber's 

 test-bottle. 



