24 FRUITS AND FRUIT PRODUCTS. 



added color from the fruit will take up some of the natural color of 

 the food as well. 



As will be seen in Tables I and II, amyl alcohol extracts the coloring 

 matter from many fruits, and these extracts may easily be mistaken 

 for added colors. 



Some of the highly colored fruit juices will dye wool, and the color 

 will be permanent, but these will not be mistaken for coal-tar dyes if 

 the double dyeing method is followed. 



Mixtures of two or more dyes are often added to foods. This can 

 sometimes be shown by a system of fractional dyeing where the dyes 

 are taken up at different rates by the fabric. In examining mixtures 

 of red, orange, and blue dyes, which are widel} 7 sold for coloring wine, 

 the writers found that the woolen cloth took up the red much faster 

 than the orange, and the blue was slowest; so that the first piece of 

 cloth dyed was red, the second a lighter shade, the third greenish, and 

 the fourth bluish. 



In the examination of the coloring matter for the heavy metals, 

 tin, lead, copper, and zinc will be found in the ash, and tests can be 

 made for them by the methods used for heavy metals. 



DETECTION OF COAL-TAR COLORING MATTERS BY DYEING WOOL. 



Method of Sostegni and Carpentieri.* From 10 to 20 grams of the 

 sample are dissolved in 100 cc of water, filtered if necessaiy, acidified 

 with from 2 to 4 cc of a 10 per cent solution of hydrochloric acid, and 

 a piece of woolen cloth which has been washed in a very dilute 

 solution of boiling potassium hydroxid and then washed in water, 

 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. 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 matter this sec- 

 ond dyeing gives practically no color, and there is no danger of mis- 

 taking a fruit color for one of coal-tar origin. It is absolutely neces- 

 sary that the second dyeing should be made, as some of the coal-tar 

 dyes will dye a dirty orange in the first acid bath which might be 

 easily passed for vegetable color, but on treatment in alkaline bath 

 and second acid bath becomes a bright pink. 



Arata's method.* This method gives results comparable with those 



a Ztschr. anal. Chem., 1896, 35, 397; U. S. Dept. Agric., Div. Chem. Bui. 46, revised, 

 p. 68. 



b Ztschr. anal. Chem., 1889, 28, 639. 



