COLORING MATTER. 191 



(b) ARATA'S METHODS 



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

 preceding method. It was recommended for detecting coal-tar colors in wine, 

 and has been used by Winton & in fruit products. 



Boil from 20 to 30 grams of the sample dissolved in 100 cc of water 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, wash the wool in boiling water and 

 dry it 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 ammonium hydroxid and not restored 

 by washing. 



In addition to this, it is advisable in all cases to dissolve out the coloring 

 matter with ammonium hydroxid 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 confirmed 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 coloring matter can be identified to a certain extent by the 

 s of Witt/' Allen, d Weingartner/ Dommergue/ Girard and Dupre,^ and 

 The tests can be made directly on the dyed fabric or the dye can be 

 dissolved out* 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, 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 ammonium hydroxid, 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 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 ; 

 tropa?olin OOO and solid red give violet. 



If the wool is well dyed, most of these colors may be obtained on the fabric. 



These are the reactions of only a few of the more common colors ; in order to 

 carry the work further the more complete works mentioned must be used. 



ffl Zts. anal Chem., 1889, 28: 639. 



6 Conn. Agr. Exper. Stat. Kept., 1899, Part 2, p. 131. 



"Zts. anal. Chem., 1887, 26: 100. 



* Commercial Organic Analysis, 3 (1) : 399-420. 



* Zts. anal. Chem., 1888, 27 : 232-249. 

 'Zts. anal. Chem., 1890, 29: 369-377. 



' Analyse des matieres alimentaires, etc., 583-593. 



* Analyst, 1899, 24: 41. 



1 Zts. anal. Chem., 1889. 28: 639: Rorgmann. Analyse <l<-s \\Vines, p. 1)1; Winton, 

 Conn. Agr. Exper. Stat. Kept., 1899, Part 2, p. 131. 



