METHODS OF ANALYSIS FOB CERTIFIED COLORS. 219 



SULPHATED ASH. 



Determine as given under Naphthol Yellow S, page 214. 



CALCIUM. 

 Determine as given under Naphthol Yellow S, page 215. 



SULPHUR. 

 Determine as given under Naphthol Yellow S, page 215. 



NITROGEN. 



Determine as given under Ponceau 3R, page 217. 



TEST FOR ORANGE II (SMITH AND MATHEWSON's METHOD). 



The following solutions are required: 



(1) Fifteen per cent titanium trichlorid. 



(2) Freshly prepared diazotized sulphanilic acid. Heat a mixture 

 composed of 1 gram of sulphanilic acid, 10 cc of water, and 20 cc of 

 concentrated hydrochloric acid on a steam bath for five minutes with 

 occasional shaking. Cool to about 10 C. and add slowly 10 cc of a 1 

 per cent solution of sodium nitrite. Allow the mixture to stand at 

 about 10 for 10 minutes, dilute to 1 liter, and shake until all the 

 solid particles have dissolved. 



(3) Stannous chlorid, prepared by dissolving 40 grams of stannous 

 chlorid in 100 cc of concentrated hydrochloric acid. Dilute this ten 

 times with water, immediately before using. 



Place 2 cc of a 0.1 per cent solution of the dye in a colorimeter tube 

 having a capacity of about 100 cc, add a small drop of titanium trichlo- 

 rid solution and shake until the mixture is decolorized. Standards 

 containing the same quantity of color composed of a mixture of pure 

 Orange I and known amounts of Orange II are treated in the same 

 way, the volume of the solution at this point to measure less than 5 cc. 

 Dilute the decolorized solutions to 50 cc with 95 per cent alcohol and 

 equalize the temperature by immersing the tubes in water at room 

 temperature. (Note. A slight coloration that may develop at this 

 point may be disregarded.) Allow the tubes to stand in the water 

 for about five minutes, add 2 cc of the diazotized sulphanilic acid, 

 and mix thoroughly. If the titanium trichlorid has not been used 

 in too great excess, the first few drops of the diazotized sulphanilic 

 acid will cause a formation of color. Allow the coupling to proceed 

 for three minutes and then add 5 cc of the diluted stannous chlorid 

 with vigorous shaking. In two minutes the blue color due to Orange I 

 will disappear, leaving only the pink caused by the coupling product 

 of Orange II. The depth of color in the tube containing the dye 

 under examination may then be compared to the standards. 



