230 



Further, suppose the method is accurate, how would the analyses show that the citral 

 used was obtained from lemon oil or the commercial citral obtained from lemon grass 

 oil? 



AN OUTLINE TO ASSIST IN THE IDENTIFICATION OF CERTAIN 

 WATER-SOLUBLE COAL-TAR COLORS. 



By C. B. COCHRAN*. 



The reactions given by the coal-tar colors listed in the following outline were all 

 obtained with solutions as dilute as they could be made and still give reactions suffi- 

 ciently clear and definite to furnish a ba^is for positive contusions. Because of the 

 degree of dilution the results here tabulated will, in some cases, appear contradictory 

 to those given by Schultz and Julius. For example, these authors may report a color 

 precipitated by a certain reagent when the precipitation is only partial and therefore 

 does not appear in dilute solutions such as have been used in the preparation of these 

 tables. 



The sodium bisulphite reagent is prepared by saturating a 5 per cent solution of 

 sodium hy droxid with sulphur dioxid . The absorption tests with aluminum hydroxid 

 were made by adding between 2 and 3 cc of well-washed aluminum hydroxid (from 

 which the excess of water has been drained through the filter) to 10 cc of the color 

 solution. 



The tests with the fuller's earth were made by adding 2 cc of the earth to 10 cc of 

 the color solution. In these absorption tests the aluminum hydroxid and fuller's 

 earth are shaken with the color solution. If, after setting, the supernatant liquid is 

 colorless or very nearly so, the result is recorded as color absorbed. In the majority 

 of cases the results obtained with aluminum hydroxid and fuller's earth are definite 

 and sharp. There are many colors belonging to Class I (Rota's classification) which 

 are much more readily absorbed from their water solutions by aluminum hydroxid 

 than by fuller's earth, while the reverse is true of many colors belonging to Classes 

 II, III, and IV. 



In the dyeing tests sodium carbonate was used for making alkaline and hydrochloric 

 acid for acidifying. The alkali solution was very weak and the acid bath about one- 

 half the official strength (1 cc strong hydrochloric acid to 50 cc). 



The numbers following the names of the colors refer to the 1904 edition of Green's 

 tables. 



COAL-TAR COLORS OF CLASS I. 



Solution reduced and in most cases decolorized by ptannous chlorid. Original 

 color not restored by hydrogen dioxid. 



DIVISION I. COLOR ABSORBED BY ALUMINUM HYDROXID. 



Dye wool red. 



SECTION I. Color precipitated by sodium bisulphite reagent. 



Congo red (A) (240) dyes wool and unmordanted cotton red from neutral or faintly 

 alkaline bath, but not from acid bath. Oxalic acid or acetic acid gives a blue precipi- 

 tate and colorless filtrate. 



SECTION II. Color not precipitated nor solution changed by sodium bisulphite 

 reagent. 



Fast red A (102), hydrochloric acid gives a brown precipitate and colorless filtrate. 

 Dyes wool and unmordanted cotton red from acid, alkaline, or neutral bath. Color 

 precipitated by barium chlorid solution. 



