CHEMISTRY. 183 



Alizarine can be obtained in yellow, needle-shaped crystals by 

 simple sublimation from the dried madder, although it is not 

 regarded as existing as such in the madder-root. A crystalline 

 glucoside, termed rubianic acid (Schunck), is contained in the 

 root, and this splits up into alizarine and glucose. The formula 

 assigned by Schunck to alizarine was C^HioO^ while Strecker 

 held it to be CioH c O 3 . Some five years since, Martins and Griess 

 obtained a coloring matter possessing Strecker's formula ; it was 

 not, however, alizarine, but was supposed to be isomeric with it. 

 Some time after the discovery of this supposed isomer of alizarine, 

 Graebe commenced his researches on quinone. In these researches 

 when it had been shown that chloroxynaphthalic acid was a qui- 

 none acid, Graebe and Liebermann thought it probable that aliza- 

 rine belonged to the quinone series. On treating a specimen of 

 the natural coloring matter with powdered zinc, they obtained a 

 substance of the composition Ci 4 Hio. This hydrocarbon formed 

 with picric acid a red compound and, in fact, possessed all the 

 properties of anthracene as obtained from, coal-tar. Having 

 obtained anthracene from alizarine, it now remained to form aliza- 

 rine from anthracene ; and in this Graebe and Liebermann were 

 successful. (Their process was noticed in the preceding volume 

 of the " Annual of Scientific Discovery," p. 205.) Heating anthra- 

 quinone (Ci4H 8 O 2 ), an oxygenated derivative of anthracene dis- 

 covered by Laurent, with bromine, they obtained a brominated 

 compound (Ci4H 6 BroO 2 ) , which, on being treated with caustic 

 potash at a temperature of 180 C., yielded the potassium salt of 

 alizarine. From this alizarate of potassium the alizarine is sep- 

 arated by chlorhydric acid. This process has since been modified 

 by the substitution of a cheaper reagent in the place of bromine. 

 This reagent is found in common sulphuric acid ; on heating an- 

 thraquinone with sulphuric acid at a high temperature, a sulpho- 

 acid is formed (Ci4H c O 2 ,2HSO 3 ), which, on treatment with hydrate 

 of potassium, yields alizarate of potassium and sulphite of 

 potassium. 



Artificial alizarine is entirely identical with the coloring matter 

 obtained from the madder-root. Both products crystallize in 

 needles which are usually curved, especially when small. They 

 dissolve in caustic alkalies, forming violet solutions of the same 

 tint. When applied to mordanted fabrics, they produce exactly 

 the same colors, bearing the treatment with soap equally. They 

 possess also precisely the same tinctorial value. When dissolved 

 in alcohol they produce, with acetate of copper, a purple solution 

 of precisely the same shade of color. When examined with the 

 spectroscope, their potassic solutions produce the same absorption- 

 bands. A good deal has been said about anthracene, it being 

 assumed that it cannot be obtained in large quantities. It must 

 be remembered, however, that tar distillers have had, as yet, but 

 little experience in separating this substance. Mr. Perkin believes, 

 from his experiments, that coal-tar contains considerable quanti- 

 ties of this hydrocarbon. 



There can be no doubt that the kind of coal, as well as the tem- 

 perature employed in the gas-works, infiuences the quality of the 



