26 ELEVENTH REPORT. 



SOME RECENT OR ADVANCED METHODS IN THE ANALYSIS OF 



MILK. 



W. E. RoBisox. 



I think ten minutes will amply suffice in which to tell you what we are doing 

 in regard to "Recent or Advanced Methods" in the analysis of milk at the 

 Dairy and Food Department. First of all^ our work is quite necessarily 

 limited to the study of adulteration of food and drink products. Therefore, 

 the methods which are under study in regard to milk are methods chiefly 

 for the determination of water, that being the chief adulterant of milk, as 

 well as of sausage and a great many other food products, and some products 

 which are not foods. 



In our study of milk by the common methods of analysis, while we have 

 been able to state with comparative certainty when a milk has been grossly 

 watered, we have not been able to state with any degree of accuracy to what 

 extent it has been adulterated, because we do not know the composition of 

 the original milk, and to assume that a given sam]:)le of milk is adulterated, 

 either skimmed or watered, because it falls short of the arbitrary require- 

 ments of the statute, is to work injustice in many cases. For instance, the 

 milk of Coloma Canary of the college herd, referred to in table below, is below 

 the standard i-e(}uired by the statute, yet is not adulterated, while on the 

 contrary, the milk of Daisy or Bonnie May might be quite badly adulterated 

 and still be within the statute. 



We may l)e able to say from the more common methods of analysis however, 

 that a sample contains at least lO'^x or 20*^0 added water, as the case may 

 l)e. But is it not possible that something more definite can be ascertained? 

 In order to satisfy ourselves on this ciuestion, we have been led to the use of 

 the Zeiss Immersion Refractometer, and Beckman's apparatus for the 

 determination of the freezing point depression of liquids. And while the 

 refractometer proves of great value when used as cumulative or corroborative 

 evidence, it does not enable us to answer the question "how much?" Both 

 methods are l:)eing used to some extent in some of the foremost laboratories 

 in this country and abroad. In the comparatively small amount of work I 

 have done with them together, I have found that the freezing method gives 

 closer results than the refractometer, and I wish to call your attention to some 

 of the data in hand as given in the table below. 



Now for the purpose of ascertaining the effect of added water, I have 

 taken a portion of the milk of the Jersey and diluted it very carefully with 

 distilled water, making additions of 50%, 25%, 10%, 5%, and 2^% respec- 

 tively, and the freezing point depressions are as given in the talile. It will 

 he noticed that this checks within exceedingly narrow limits with the theore- 

 tical, and using so many different pipettes in the samjiling may possibly 

 explain a part of the slight variation. This data gives us a very good view 



