detkctio:n of foreign coloring matter. 23 



BENZOIC ACID, 



Mohle-f^i-i te.^f. — Treat a second portion of the extract with '1 to 8 cc 

 of strono- sulphuric acid, and heat until white fumes appear. By this 

 means benzoic acid is converted into sulphobenzoic acid. Add a few 

 cr^'Stals of potassium nitrate, and continue the heating, with repeated 

 additions of potassium nitrate until the solution is colorless or of a 

 ver\^ light yellow color. This causes the formation of metadinitro- 

 benzoic acid. When cool dilute with about 5 cc of water, neutralize 

 with anunonia. and transfer to a test tube. Filter if not clear or if 

 crystals of anunonium or potassium sulphate separate. Add to the 

 filtrate a few drops of ammonium sulphid, care being taken that it 

 does not mix but forms a laver on the top. The nitro compound 

 becomes converted into the ammonium metadiamidobenzoate. which 

 possesses a bright cherry- red color. The reaction takes place in a few- 

 seconds, and is readih' seen at the plane of contact of the two liquids. 

 This reaction is also given by saccharin, but benzoic acid may readily 

 be separated from saccharin by distillation and the test applied to the 

 extract from the distillate. 



SACCHARIN. 



Saccharin is indicated by the sweet taste of the ether extract. To 

 confirm this test, add to the remaining portion of the extract 1 or 2 

 grams of sodium h3^droxid, and heat in an oil bath at a temperature 

 of '2b(f- C. for from twenty to thirty minutes. The saccharin is con- 

 verted into "Salicvlic acid." After cooling, dissolve in water, acidifv 

 with dilute sulphuric acid, extract with ether, and test for salicylic 

 acid as described under salicTlic acid. If salicylic acid is present in the 

 original material this test, of course, can not be applied, but reliance 

 must in that case be placed in the sweet taste of the extract. 



DETECTION OF FOREIGN COLORING MATTER. 



The complete examination of dyes is too large a subject to take up 

 here, and one will have to refer to such works as Schultz and Julius 

 on Organic Coloring. Allen's Commercial Organic Analysis, and others 

 that go into the subject in an exhaustive manner. The determination 

 of the general nature of the dye can be made b}' the use of Rota's** 

 scheme, which is the simplest of the many different methods proposed 

 and is quite satisfactory, although it requires a great deal of care and 

 experience. 



The detection of the color in a fruit product and its identification are 

 rather difficult, since the color must be separated in a somewhat pure 

 condition and then tested. Almost all the methods for separating 



"^Chem. Ztg., 1898, 22, pp. 437-442; Analyst, 1899, 24. p. 41; V. S. Dept. of Agric, 

 Bureau of Chem. Bui. t>5, p. 114. 



