112 PROVISIONAL METHODS FOE ANALYSIS OF FOX)DS. 



potassium hydroxid and then washed in water, is immersed in it and boiled for five 

 to ten minutes. The cloth is removed, thoroughly washed in water, and boiled with 

 very dilute hydrochloric acid solution. Then after washing out the acid the color is 

 dissolved in a solution of ammonium hydroxid (1 to 50). With some of the dyes 

 solution takes place quite readily, while with others it is necessary to boil some time. 

 The wool is taken out, a slight excess of hydrochloric acid is added to the solution, 

 another piece of wool is immersed and again boiled. With vegetable coloring mat- 

 ter this second dyeing gives practically no color, and there is 110 danger of mistaking 

 a fruit color for one of coal-tar origin. It is absolutely necessary that the second 

 dyeing should be made, as some of the coal-tar dyes a will dye a dirty orange in the 

 first acid bath which might be easily passed for vegetable color, but on solution in 

 alkaline bath the second acid bath dyes a bright pink. 



(b) ARATA'S METHOD. b 



This method gives results comparable with those of the first dyeing of the preced- 

 ing method. It was recommended for detecting coal-tar colors in wine, and has 

 been used by Winton in fruit products. 



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 hydroxid and thoroughly washed in water. After removal 

 from the solution the wool is washed in 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 out the coloring matter 

 with ammonia as in the first method and dye again, since Arata's method gives prac- 

 tically 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 vegetable coloring matter has been excluded. The col- 

 oring matter can be identified to a certain extent by the schemes of Witt, d Allen, 

 Weingartner, e Dommergue, f Girard g and Dupre, and Rota. h The tests can be made 1 

 directly on the dyed fabric or the dye can be dissolved out. j 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 with strong sulphuric acid. 



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



Ponceau S and tropaeolin O give yellow to orange yellow. 



U. S. Dept. of Agr., Bureau of Chem. Bui. 66. 

 t>Ztschr. anal. Chem., 1889, 28, 639. 

 <=Conn. Exp. Sta. Report, 1899, Pt. II, p. 131. 

 aztschr. anal. Chem., 1887, 26, 100. 

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

 'Ztsch. anal. Chem., 1888, 27, 232-249. 

 sZtsch. anal. Chem., 1890, 29, 369-377. 

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

 i Analyst, 1899, 24, 41. 



JZtsch. anal. Chem., 1889, 28, 639; Borgmann, Anal, des Weines, p. 91; Winton, Conn. Expt. Sta. 

 K< !>!., 1899, Pt. II, p. 131. 



