68 DETECTION OF ADULTERATIONS. 



By subtracting the weight of the filter ash, the weight of 

 the barium sulphate is obtained. One part BaSO^ is 

 equivalent to 0.3429 part SO,. 



For the detection of nitric acid a satisfactory method is 

 to coagulate the milk by means of a solution of calcium 

 chloride free of nitrates, filter off the precipitate, and mix 

 with the filtrate a solution of diphenylamine in concentra- 

 ted sulphuric acid. In the presence of nitric acid, even of 

 minute traces of it, there appears a blue ring or zone at 

 the line of demarkation of the two liquids. 



Egger and Moslinger recommend a solution of 0.02 

 gram diphenylamine in 20 c. c. of sulphuric acid (i part 

 HjSO* and 3 parts H2O) completing the volume to 100 

 c. c. with concentrated sulphuric acid. Of this solution 

 2 c. c. are placed in a porcelain evaporator and to it 0.5 

 c. c. of the milk serum is added. The serum is obtained 

 by heating 100 c. c. of milk with 1.5 c. c. of concentrated 

 solution of calcium chloride and filtering from the result- 

 ing precipitate. After adding the serum the material is 

 allowed to stand for a moment or two, then mixed by 

 rotating the dish, again allowed to stand and again mixed. 

 In the presence of only traces of nitric acid a blue streak 

 develops around the edge of the dish and by mixing grad- 

 ually colors the whole fluid. 



Both of these methods for detecting adulteration fail 

 if distilled water containing neither sulphates nor ni- 

 trates is used as a diluent. A number of other methods 

 for this purpose have been proposed but they give only 

 approximate results. Some of them, however, are of 

 value to many workers, physicians for example, who of- 

 ten lack time and apparatus necessary for a more exact 

 test. If by one or more of these simple methods, results 

 are obtained which are considered doubtful, as will occa- 

 sionally happen, the sample may be submitted to a chem- 

 ist for a more refined chemical analysis. 



