48 MILK 



blue, sucrose a weaker blue and dextrose the 

 weakest blue, corresponding in intensity as 

 lo :3 :i. 



Stannous chlorid and ferrous sulfate give this 

 color, but the reaction takes place in the cold, 

 and with small quantities the color disappears on 

 heating. In order for the color to persist after 

 heating the sample of cream must contain these 

 substances to the extent of i % calculated as the 

 metal. In this case the sample will be completely 

 coagulated and the taste will be disagreeable. 

 Hydrogen sulfid will also give the blue, but it will 

 disappear on heating. If the solution does not 

 show blue before heating, it is free from hydrogen 

 sulfid, ferrous sulfate or stannous chlorid. 



As a confirmatory test for sugar, the resorcinol 

 test may be applied to the serum prepared with 

 uranium acetate as described. This test is given 

 by sucrose and levulose, but not by dextrose or 

 lactose. 



The quantitative estimation of sucrose in milk 

 is given under Milk Products (page 74). 



Detection of Heated Milk. — Fresh milk con- 

 tains one or more enzyms of the "peroxydase" 

 type, that is, having power to bring about 

 transfer of oxygen from peroxids to oxidable 

 substances. As the function of these enzyms 

 is destroyed by temperatures near 100°, it be- 

 comes possible to utilize the reaction for deter- 



