32 MILK-ANALYSIS. 



dropped the above-mentionel diluted milk, previously acid- 

 ulated and filtered. As the dilute milk drops from a 

 burette, it instantly reduces the boiling copper-solution, which 

 deposits red oxide of copper. The dropping is to be con- 

 tinued until the boiling copper-solution ceases to be reduced 

 until it is exhausted. The point of exhaustion is determined 

 roughly, by observing when the blue color leaves the solu- 

 tion, and. finely, by observing the exact point at which 

 ferrocyanide of potassium ceases to strike a red color with 

 the filtered solution, which must be slightly acidulated with 

 acetic acid before being tested with the ferrocyanide. The 

 standard copper-solution is prepared by dissolving 34.65 

 grammes of crystals of sulphate of copper in 200 c. c. of 

 water. To this solution is added a solution made by dissolv- 

 ing 173 grammes of double tartrate of potash and soda in 

 480 c. c. of caustic soda solution, of specific gravity 1.14. 

 The whole is diluted till it occupies the volume of one litre. 



The standard solution, so prepared, is of such a strength 

 that 10 c. c. are equivalent to 0.067 grammes of milk-sugar 

 (dry at 100 C.) 



I am not in the habit of using this process, but without 

 doubt it is occasionally of value. 



