248 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



green, alizarine sky-blue, anthraquinone blue, and alizarine sapphirole, 

 astrol, irisol, and rubinol. Their fastness to light is so excellent 

 that in the famous "Manufacture Nationale du gobelins" in Paris, 

 they have replaced the older dyestuffs for the dyeing of wool used 

 in the manufacture of gobelins. This means a great deal if it be 

 borne in mind that a square meter of these gobelins, for the produc- 

 tion of which an operator needs more than a year, costs, on the 

 average, about 6,000 francs. 



INDANTHRENE AND ALGOLE COLORS. 



An entirely new era began for tlie alizarine series when Rene Bohn 

 in 1901 found that his new color, indanthrene, could be used as a 

 vat dye for cotton. This color can be dyed in its reduced state like 

 indigo, but is far superior to the latter in beauty and brightness of 

 shade, as well as in fastness to washing and liglit. Indeed, tlie 

 fastness to light is so great in this respect it must bo termed 

 indestructible. 



On account of this phenomenal fastness, indanthrene blue caused 

 chemists to look for other vat colors in the anthraquinone series. 

 Their efforts did not remain unrewarded, and we already possess 

 colors of this class giving every possible shade. The Badische Anilin 

 and Soda Fabrik sell them under the name of ''indanthrene colors," 

 the Farbenfabriken vorm. Friedr. Bayer & Co. under the name 

 "algole colors." Chemically most of these vat colors belong to the 

 indanthrene type; some of them are still more complicated nuclear 

 products of condensation of several anthraquinone molecules; others, 

 again, rea di- and tri- anthraquinonyl amines. It must also be noted 

 that to the greatest surprise of all experts in this branch, it was dis- 

 covered in the laboratory of the Faibenfabrikcn vorm. Friedr. Bayer 

 & Co., that even some of the sim])lest acyl derivatives (-benzoyl) of 

 the aminoanthraquinones are excellent vat colors. 



LAKE COLORS. 



We must not leave out of sight the importance of some colors of 

 the aniline group and especially the antliraquinone group for the 

 production of lakes for paints and pigment colors for wall paper. 

 The alumina lake of alizarine, the so-called madder lake, with its 

 fine shade and great fastness to light, is best known. Other alizarine 

 colors also yield valuable alumina lakes; thus, alizarine sapphirole 

 gives a blue lake of excellent fastness to light. But it is not always 

 necessary to precipitate lakes. Some of the difficultly soluble vat 

 colors may be directly employed in a fmely divided form. Thus 

 indanthrene and algole blue already play important roles as substi- 

 tutes for ultramarine for bluing higher class paper, textiles, and even 

 sugar. 



