DETECTION OF FOREIGN COLORING MATTER. 25 



of the first dyeing of the preceding method. It was recommended for 

 detecting coal-tar colors in wine, and has been modified by A. L. 

 Win ton. a 



From 20 to 30 grams of the sample dissolved in 100 cc of water are 

 boiled for ten minutes with 10 cc of a 10 per cent solution of potassium 

 bisulphate and a piece of white wool or woolen cloth which has been 

 previously heated to boiling in a very dilute solution of sodium 

 h ydroxid and thoroughly washed with water. After removal from the 

 solution the wool is washed with boiling water and dried between filter 

 papers. If the coloring matters are entirely from the fruit the wool 

 will be either uncolored or will take on a faint pink or brown, which 

 is changed to green or yellow by ammonia and not restored by washing. 



In addition to this it is advisable in all cases to dissolve the col- 

 oring matter with ammonia as in the first method and dye again, since 

 Arata's method gives practically the same results as the first dyeing in 

 hydrochloric acid bath, and needs to be substantiated by the second 

 dyeing. 



Another advantage in the second dyeing is that if a large piece of 

 woolen cloth is used in the first dyeing and a small piece in the second 

 dyeing small amounts of coloring matter can be brought out much 

 more decidedly in the second dyeing where practically all of the vege- 

 table coloring matter has been excluded. The coloring matter can be 

 identified to a certain extent by the schemes of Witt, 1 ' Allen, c Wein- 

 gartner, d Dommergue, 6 Girard and Dupre/ and Rota. g The tests can 

 be made directly on the dyed fabric or the dye can be dissolved out. h 

 To remove the color wash the wool with dilute tartaric acid and then 

 with water and dry between filter paper. Saturate the wool with 

 strong sulphuric acid and press out the color with a glass rod after 

 from five to ten minutes and dilute to 10 cc with water. 



Remove the wool, make solution alkaline with ammonia, and when 

 cold extract with from 5 to 10 cc of amyl alcohol. Separate the amyl 

 alcohol, evaporate it to dryness, and test the residue. Treat this residue 

 with strong sulphuric acid. 



Ponceau R, 2ll, 3R, S, and 3S give yellow red to carmine red. 



Ponceau S and tropaeolin O give yellow to orange yellow. 



Biebrich scarlet gives a green; Bordeaux red and crocein scarlet 

 give blue; tropaeolin OOO and solid red give violet. 



11 Conn. Exp. Sta. Kept., 1899, Pt. II, p. 131. 

 h Ztsc.hr. anal. Chem., 1887, 26, 100. 

 c Com. Org. Anal., Vol. Ill, pt. 1, pp. 399-420. 

 d Ztschr. anal. Chem., 1888, 27, 232-249. 

 c lbid., 1890, 29, 369-377. 



r Analyse des Matieres Alimentaires, etc., 583-593. 

 g Analyst, 1899, 24, 41. 



h Ztschr. anal. Chem., 1889, 28, 639; Bor 8 AI, Anal, des Weines, j>. 91; Winton, 

 Conn. Expt. Sta. Kept., 1899, Pt. II, p. 131. 



