428 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



the filter; but since all the common aniline colors leave a re- 

 siduum, this is no safe test. The comparison of the intensity 

 of a solution of aniline of acknowledged purity with that to 

 be examined gives the best indication ; and if the price of 

 the compound be established only in proportion to its dye- 

 ing power, there will be but a small inducement for fraud. 

 14 (7, 1871, vol. 194, v., 514. 



PREPARATION OF CARMINE PUEPLE. 



The dye recently invented, and known as carmine purple, 

 is obtained by the solution of uric acid in nitric acid, care be- 

 ing taken to prevent boiling over and too great an increase 

 of temperature. The mixture should remain standing quiet- 

 ly for some days, after which a thick, pasty, or doughy sub- 

 stance is obtained, which is to be treated with warm water, 

 filtered, and the residuum again treated with warm water. 

 The filtered liquid possesses a reddish or yellowish color, re- 

 sulting from the organic substances decomposed by the nitric 

 acid. This liquid is now a mixture of alloxan, alloxantin, 

 urea, paraban acid, dialuramid, and other products of uric 

 acid. It is next to be evaporated in a large enameled iron 

 vessel, but not heated to the boiling point, which would de- 

 stroy the murexide produced. 



After the liquid has been evaporated to a sirupy consisten- 

 cy, and has assumed a beautiful brownish-red or violet color, 

 it is to be allowed to cool. The entire quantity of the liquid 

 should never be evaporated at one time, nor heated to the 

 boiling point. 26 (7, xm., 1871, 207. 



SEPAEATION OF INDIGOTINE. 



Messrs. A. A. Aguiar and A. Bayer publish as new a sim- 

 ple process by which they obtain pure indigotine, or the dye- 

 ing principle of the indigo of commerce, using aniline as a 

 solvent. Pulverized indigo and pure aniline are to be heated 

 to boiling in a flask, when the organic base almost instanta- 

 neously dissolves the coloring matter, and becomes a deep 

 blue liquid, very much like a concentrated solution of indigo 

 in sulphuric acid. This is filtered, and the residue treated 

 with aniline as long as coloring matter is dissolved. Most 

 of the indigotine crystallizes in the cooling solution within a 

 lew hours, and the remaining liquid becomes black from the 



