210 COAL-TAB COLORS USED IN FOOD PRODUCTS. 



and betanaphthol is used in making the seven permitted colors, and 

 since the heavy metals can be and are kept out of these two substances 

 to the extent required by the Pharmacopoeia, there seems to be no 

 good reason why they should not be kept out of the seven permitted 

 colors when made for use in food products. 



Since all these defects in the seven permitted colors can be obviated 

 in their first stage of manufacture (as is shown in the case of para- 

 nitranilin and betanaphthol, and in some actual commercial samples 

 of 1907, see sections XIV and XV), they are commercially avoidable 

 at subsequent stages of manufacture, and there is no good reason why 

 they should be then introduced. 



XVII. METHODS OF ANALYSIS USED IN TESTING COLORS FOE 



CERTIFICATION. 



INTRODUCTION. 



The exact analytical methods developed and tested in the New 

 York Food and Drug Inspection Laboratory and used in obtaining 

 the analytical data contained in the preceding chapter are described 

 in the following pages. These descriptions were written by A. F. 

 Seeker, of that laboratory, under whose immediate supervision all the 

 laboratory work was done, and they represent a great deal of work, 

 extending over more than three years. The methods are submitted 

 in the hope and expectation that in their wider application by a larger 

 number of chemists any defects in the methods or conclusions drawn 

 from the results will be detected and rectified. Experience in the 

 New York laboratory has shown that even different chemists of 

 varying degrees of experience in this particular line of work obtain 

 concordant duplicates after a comparatively short laboratory 

 acquaintance with these methods. 



The identity of these colors and their freedom from foreign dyes is 

 shown by the close agreement of their elements, as determined by 

 analysis, with their theoretical composition; their behavoir toward 

 reagents as given by standard works on dyes; their distribution 

 between the layers when neutral, alkaline, and acid aqueous solutions 

 are shaken with various immiscible solvents; uniformity of shade in 

 the spots produced by particles of the dry color blown over the surface 

 of wet filter paper, or water, and over concentrated sulphuric acid; 

 uniformity of shade produced by a 0.5 per cent dyeing on wool under 

 standard conditions, with similar dyeings from fractions produced by 

 partial precipitation, by partial salting out, by fractional crystalliza- 

 tion, and by extraction with alcohol or some liquid in which the pure 

 color is not very soluble; and the behavior of the dye in acid and 

 alkaline solution toward cotton. Which of these tests are needed to 

 prove conclusively the identity of certain dyes or to establish their 



