iv PRESERVED MILK 215 



determine the quantity of this sugar along with the milk sugar 

 the method employed for condensed milk (p. 213) can be used. 



If the dried milk contains carbonate or bicarbonate of soda, 

 either of these may be easily detected by the alkaline reaction 

 which the powder moistened with water shows to litmus paper. 



Adulteration of desiccated milk with foreign substances is 

 not likely, but it is advisable to subject it to a microscopic 

 examination in addition to the chemical. When starch has 

 been added it is easily detected by the blue coloration with 

 iodine. 



V. CASEIN. 



The dry powdered casein which is used for various technical 

 purposes varies in purity according to the method of manufac- 

 ture. Sometimes sand is found along with the casein, or 

 if insufficiently washed some of the acid used for the pre- 

 cipitation of the casein may be present. Small quantities of 

 milk sugar, etc., are also sometimes present. A marked 

 yellow colour points to the presence of large quantities of lime 

 salts. The amount of sand is easily determined by ignition, 

 treatment with dilute hydrochloric acid, filtration, burning of 

 the filter and weighing of the sand. The presence of hydro- 

 chloric or sulphuric acid is detected as usual by an addition 

 of AgNO 3 or BaCl 2 in the ordinary way. Milk sugar is 

 estimated by Fehling's solution, and the percentage of casein 

 by determining the nitrogen by Kjeldahl's method and multi- 

 plying the amount found by 6'38. 



