SOME PHYSICO-CHEMICAL MASUREMENTS ON MILK. 187 





Table VIII. 





5,M.F. 



H ion. 



H ion (indicator). 



•7334 



6*86 



6*85 



•6645 



5*66 



5-70 



•6225 



4*93 



5*00 



•6042 



4'62 



4-70 



•5870 



4*42 



4*35 



In determining the H ion concentration of the milk at 

 any time, a number of ordinary test tubes of the same bore 

 and thickness were used. A solution of the indicator (1 

 drop to 20 cc. of water) was made, and 10 cc. of this 

 solution delivered to each tube. Having prepared a number 

 of tubes in this way, two drops of a solution of known H 

 ion concentration were added to the first tube, then the 

 same amount of a different concentration to the second 

 tube, and so on, until a sufficient number of tubes were 

 obtained containing different intensities of colour. It was 

 found that two drops of any of the above solutions were 

 sufficient to give an intensity of colour closely approxi- 

 mating to the maximum colour. The change produced by 

 a further addition of H ion of the concentration previously 

 added being negligible when compared with the change in 

 intensity due to a solution *1 higher in its H ion concen- 

 tration. 



A similar experiment with milk instead of one of the 

 standard solutions enabled a comparison to be made between 

 milk and these solutions, and so gave the desired figure 

 for the concentration of H ion. In this case the colour 

 produced was destroyed after about 12 hours. In obtaining 

 a sample of milk the cow was milked without special 

 precautions, the milk well mixed and a portion received 

 into a sterilized bottle the neck of which was closed with 

 cotton wool, so that the subsequent decomposition was 

 due to the micro-organisms which gained access during the 

 milking process. 



