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cerit of butter. One good Indian cow giving 5 or 6 seers of 

 milk per day should produce annually 100 Ibs. of butter or 

 250 Ibs. of cheese. An average English dairy cow produces 

 twice as much. One pound of cheese is obtained from about 

 ten pounds of whole-milk or fifteen pounds of skim-milk. The 

 produce of cheese is a more reliable test of the purity of milk 

 than the produce of butter. 



1,130. As cow's and buffalo's milk contain almost the uni- 

 form proportion of 5 per cent, of lactose and as the lactose is 

 converted by souring into lactic acid, the estimation of the 

 percentage of lactic acid in a sample of sour milk is a still 

 fairer and a more feasible test of the purity of milk. The 

 exact proportion of lactic acid contained in a sample is found 

 out by the following titration test : 



Take one 50 c. c. burette with glass tap ; one burette 

 stand ; one 50 c. c. test measure ; one piece of glass rod ; a 

 glass tumbler or white tea cup ; xoz. alcoholic solution of 

 phenol phthalein (i in 500); and \ gallon decinormal solution 

 of caustic soda (i. e. 4 grammes of pure caustic soda to i 

 litre of distilled water). Then take a sample of the sour 

 milk, after it has stood for at least half an hour at or near 

 the temperature of 6oF. Shake the whole to get a fair 

 sample. Measure 50 c. c. and transfer to a tumbler or 

 tea cup. Wash out the measure to get all the milk 

 and add this water to the sample. Into this stir with 

 the glass rod 6 drops of the indicator or phenol phthalein 

 solution. Fill the burette up to zero with the decinormal 

 solution of alkali. Turn the tap and allow it to flow 

 on to the milk containing the indicator. Keep up a brisk agi- 

 tation with the glass rod. A bright pink colour develops as 

 soon as the alkaline solution reaches the milk, but as rapidly 

 disappears as the stirring is maintained. A point however 

 is reached when the pink colour becomes permanent, and is 

 observed throughout the milk. Turn off the fluid quickly 

 by means of the tap, and then read off the register of the 



