214 COAL-TAK COLORS USED IN FOOD PRODUCTS. 



dipped in a 5 per cent alcoholic solution of mercuric chlorid and then 

 dried. (NOTE. It has recently been found that mercuric bromid yields 

 stains that are more evenly distributed and also produces standards 

 that are incomparably more permanent.) For purposes of com- 

 parison it is better not to develop* the strips stained by the arsin, 

 though some prefer to dip the stains in ammonium hydroxid, which 

 causes them to become black. A blank is run with each set of 

 determinations. 



ETHER EXTRACTIVES*. 



Dissolve 10 grams of color in 150 cc of water and extract in a separa- 

 tory funnel with ether that has been washed with water (using three 

 150 cc portions of water for each liter of ether). Extract the color 

 solution with two 100 cc portions of this ether, shaking thoroughly 

 for one minute, and wash the combined ether extract successively 

 with 35, 20, and 10 cc of water made alkaline or acid, as the case 

 requires, with 1 cc of tenth normal alkali or acid per 100 cc of w^ater. 

 Decant the ether from the mouth of the separately and rinse the funnel 

 once with 5 cc ether. The color solution is first extracted neutral, 

 the extracted solution being then rendered alkaline with 2 cc of a 10 

 per cent solution of caustic soda and again extracted with two 100-cc 

 portions of ether. In acidifying for the third extraction, add twice 

 the amount of hydrochloric acid (1 to 3) necessary to neutralize the 

 alkali, and repeat the extraction with two 100-cc portions of ether. 

 Place the neutral, alkaline, and acid extracts in a dust-free atmosphere, 

 and allow the ether to evaporate spontaneously, after which dry the 

 residues to constant weigh over sulphuric acid, using flat-bottomed 

 dishes 2f inches in diameter, 1J inches in height, and of about 100 cc 

 capacity. The dishes should be thoroughly cleaned, wiped dry, and 

 allowed to stand in a sulphuric acid desiccator at least two hours 

 before weighing. In order to avoid the generation of static charges 

 of electricity, they should not be wiped immediately before weighing. 

 Run two blank determinations with each series of ether extracts, and 

 deduct the average gain in weight of these two blanks from the weights 

 obtained in the other determinations. 



SULPHATED ASH. 



Weigh accurately 0.5 to 1 gram of the color into a wide platinum 

 dish, moisten with concentrated sulphuric acid, and ignite cautiously, 

 avoiding spattering; moisten the residue repeatedly with sulphuric 

 acid and ignite until all the carbon is removed and a white or reddish 

 ash is obtained. This is finally ignited at a fairly bright red heat, 

 cooled, and weighed. The aqueous solution of this ash should 

 be neutral to litmus, and may be used in a quantitative test for 

 potassium. 



