COLOR REACTIONS OF DYED FIBER. 



In the tests reported in Table III the wool was dyed with one-half 

 per cent of coal tar color in every case; in the case of natural color- 

 ing matters the amount used was about ten times greater. A piece 

 of dyed zephyr yarn about 1 inch long was covered with 2 or 3 cc of 

 the reagent in a small porcelain dish. Unless the color of the reagent 

 became marked nothing is noted in the column marked " solution" in 

 the table. The color reactions were observed three or four minutes 

 after the addition of the reagent. The dyed fiber should be dry in 

 making these tests to prevent charring of the fiber by the strong acids. 



REACTION OF COLORS IN AQUEOUS SOLUTION AND WITH 

 CONCENTRATED SULPHURIC ACID. 



While similar tables have been prepared by other workers, consid- 

 erable uncertainty arises in using them, and it has been the aim of the 

 writer in preparing these tables to be somewhat more precise in the 

 description of these reactions. As one means to this end, in Table IV 

 the approximate strength of the color solution used (about 0.01 per 

 cent) is indicated by the color of the solution in a test tube three- 

 quarters of an inch in diameter. As before stated, the solutions of 

 natural coloring matter are about ten times stronger than those of the 

 coal-tar dyes, namely, 0.1 and 0.01 per cent, respectively. About 5 cc 

 of color solution, 0.2 gram of zinc dust, and 10 drops of concentrated 

 hydrochloric acid were used for the reduction test, and approximately 

 10 cc of color solution for the other reactions in aqueous solution. 



The dry color test with concentrated sulphuric acid was conducted 

 as follows: 



About 0.01 gram of coal tar color, or 0.05 gram of natural coloring 

 matter, was dissolved by shaking with 5 cc of concentrated sulphuric 

 acid in a test tube. The solution was diluted with water, 3 to 5 cc at 

 a time, until the volume reached about 20 cc, then more rapidly with 

 constant shaking, noting any changes in the appearance of the solution, 

 until such change seemed merely to affect the depth of the color. 



[Cir. 35] 



