614 FAT-CONTENT AND ELECTRICAL CONDUCTIVITY OF MILK, 



Tt has been found that, in a given sample of milk, the depres- 

 sion of conductivity is directly proportional to the fat-content; 

 but tliat, in different samples of milk, the removal of equal 

 amounts of fat does not lead to equal increments of conductivity. 

 Various other properties of the milk have been examined in the 

 endeavour to account for this difference between samples, but no 

 definite correlation has been found. 



1. Itelati07i between the fat-content of a sample of milk and its 

 electrical cond/activity.— Mixtures of the same sample of milk 

 with different percentages of fat were prepared by spinning the 

 .samples in a centrifuge to remove as much of the fat as possible, 

 and mixing various proportions of the spun and the whole milk. 

 The conductivities of these mixtures of known fat-content were 

 determined. 



The percentages of fat in the spun and whole milk were de- 

 termined by the Rose-Gottlieb method; the percentages of fat 

 in the various mixtures were obtained by calculation. The 

 results have errors of not more than 2%. 



The electrical conductivities were determined at 25''C., by the 

 Kohlrausch method; a Wolff's Wheatstone-bridge was used, with 

 a telephone as a null instrument The determinations were 

 made in a conductivity- vessel provided with vertical electrodes. 

 The measurements obtained were concordant to 0*5%. The 

 details of these methods are given in a previous paper (Wardlaw, 

 1917). 



As the effect of the fat on the conductivity is probably related 

 more closely to the volume occupied than to the weight in a 

 given quantity of milk, some preliminary determinations were 

 made of the density of the fat in the samples examined; from 

 these figures, the volumes can be calculated. 



The density of the milk-fat was calculated from the densities 

 of the spun and the whole milk. The figures obtained are given 

 in the accompanying Table. 



