624 FAT-CONTENT AND ELECTRICAL CONDUCTIVITY OF MILK, 



Table vi. 

 Effect offal on condnrjlrihj a\id rhros^lly of milk. 



The above figures show that in these samples of inilk a de- 

 crease of 1 gm. of fat ill 100 c.c. diminished tlie viscosity from 

 3 to 7%. The corresponding increases of conductivity, however, 

 are from 30 to 50% above the values due to the volume occupied 

 by the fat. The diminution of viscosity is thus quite insufficient 

 to account for the discrepancy between the volume occupied by 

 the fat and its effect on the conductivity. It will be seen, too, 

 that the increase of conductivity is not proportional to the de- 

 crease of viscosity. 



These results also indicate that, in the samples of milk ex- 

 amined, the effect exerted on the conductivity by 1% of fat by 

 volume is as variable as the effect exerted on the conductivity, 

 and does not show that constancy which Taylor {loc. cit.) found 

 in the samples examined by him. 



5. The behaviour of fat-globules in an electric field. — If the fat- 

 globules of milk carry an electric charge, they may retard the 

 movement of ions in their vicinity, and in this way be responsi- 

 ble for the variable effect that fat exerts on the conductivity in 

 addition to the effect due to the volume displaced. The attempt 

 was made to observe whether the fat-globules were charged by 

 placing milk in a shallow cell less than 1 mm. deep, provided 

 with platinum electrodes (("hick and Martin, 1912). A current 

 was passed l)etween the electrodes, and the fat-globules were 

 watched under the microscope. No movement was observed 

 with a fall of potential below about 3 volts per cm. With higher 

 voltages, bubbles oi gas were formed at the electrodes, and 

 caused movement of the globules mechanically. These experi- 

 ments do not show conclusively that the fat-globules of milk 



