METHODS OF ANALYSIS FOB CERTIFIED COLORS. 215 



CALCIUM. 



Digest the residue from the sulphated ash determination with 

 hydrochloric acid, render the solution alkaline with ammonium 

 hydroxid, filter, and precipitate the calcium in the filtrate with ammo- 

 nium oxalate. The precipitate of calcium oxalate is filtered on a 

 tared gooch, washed, dried at 100 C. and weighed'as calcium oxalate, 

 the calcium being calculated from the formula CaC 2 O 4 .H 2 O. This 

 method is applicable only in cases where the amount of calcium is 

 very small. When the amount exceeds 0.5 per cent it should be 

 determined by digesting the sulphated ash with ammonium sulphate 

 solution made acid with hydrochloric acid, and precipitating the iron 

 by an excess of ammonium hydroxid. The precipitate is washed, 

 dissolved in hydrochloric acid, and reprecipitated, the filtrate and 

 washings being added to those obtained from the first precipitate. 

 The calcium is precipitated in the combined filtrates with ammonium 

 oxalate, the oxalate being filtered, washed, ignited, and weighed in 

 the usual way; the residue is weighed as oxid after ignition to bright 

 redness. 



SULPHUR. 



Determine upon 0.2 to 0.3 gram portions by the Carius method 

 (Gattermann, Practical Methods of Organic Chemistry, 1901, p. 81), 

 using 3 cc of fuming nitric acid (sp. gr. 1.5), and heating the sealed 

 tubes to 300 C. for at least eight hours. 



NITROGEN. 



Use the method of Dumas (Gattermann, Practical Methods of 

 Organic Chemistry, 1901, p. 85). 



PONCEAU 3B. 

 MOISTURE. 



Dry 1 to 2 grams of the finely ground dye at 109 to 110 C. in a 

 current of dry hydrogen to constant weight. 



TOTAL INSOLUBLE MATTER. 



Determine as under Naphthol Yellow S, page 211. 



NONVOLATILE OR INORGANIC INSOLUBLE MATTER. 



Determine as under Naphthol Yellow S, page 211. 



SODIUM CHLORID (SEEKER AND MATHEWSON 7 S METHOD). 



Mix 2 grams of dye thoroughly with from 2 to 3 grams of sodium 

 carbonate, moisten with water to form a paste, again mix, dry, and 

 ignite at a low red heat. By moistening, drying, and reigniting a 



