DIRT IN MILK 



301 



the vessels in which the milk is allowed to stand for a 

 few hours. It may be more quickly collected, and its 

 amount approximately estimated by means of a centrifuge. 



\ 



Ex. 143. Estimation of the sediment in milk. 



Take a carefully mixed 

 sample of the milk to 

 be examined ; not less 



than a litre should be 

 used. Add 4 c.c. of 

 formalin to it to prevent 

 the growth of bacteria, 

 and pour the milk into 

 the apparatus (Fig. 48) 

 up to 500 c.c. or the 

 litre mark. Cover the 

 opening of the cylinder 

 with a glass plate, and 

 allow the whole to stand 

 for twelve hours. Push 

 the rubber plug at the 

 end ^of the brass rod 

 through the milk to the 

 bottom of the cylinder, 

 -so as to block the outlet 

 at the bottom. Then 

 remove the measuring 

 tube and centrifuge at 

 two thousand revolu- 

 tions for three minutes. Remove the milk to just above the 

 graduated portion of the tube with a pipette, and fill up to the 

 10 c.c. mark with a .1 per cent, solution of sodium carbonate; 

 centrifuge again for two minutes. 



Read off the volume of the deposit obtained, and calculate the 

 number of volumes of sediment in i million volumes of milk. 



FIG. 48. Apparatus for estimation of sediment 

 in milk. 



