ESTIMATION OF INSOLUBLE FOREIGN 

 MATTER. 



RENCK'S METHOD. 



A liter of milk is placed in a high, cylindrical vessel 

 and allowecf to stand at least two hours, after which time 

 the greater part is removed either by decanting or 

 siphoning. To the rest containing the suspended parti- 

 cles of solid matter, water is added to make up the orig- 

 inal volume. This is allowed to stand again for two 

 hours, siphoned, and the process continued until the 

 fluid in the vessel is almost clear and no trace of milk is 

 left. The liquid is then carefully siphoned off leaving only 

 a small amount, without disturbing the sediment. The 

 sediment is then carefully filtered through a filter which 

 has been dried at 105 degrees and weighed. It is washed 

 several times with distilled water, then, to remove any 

 particles of fat contained in the sediment, it is washed 

 with alcohol and "ether, and then dried at 105 degrees to 

 constant weight, and weighed. The difference in weight 

 between the clean filter paper and that containing the 

 sediment gives directly tiie amount of foreign matter in 

 one liter of milk. According to Renck, the milk sold in 

 Berlin averages 10 milligrams to the liter. 



In order to remove the dirt and estimate the amount 

 contained in milk bottles used by dairies in delivering 



