60 KEPOR-r— 1873. 



duct distilled over, and condensed in the cool part of the tube. On collecting it and 

 purifying it by recrystallization, they found they had not a new substance, but a 

 hydrocarbon discovered as long ago as 1832 by Dumas and Laurent, and obtained 

 by them from tar. They had given it the formula C^Hj^; and as apparently it 

 thus contained once and a half as many atoms of carbon and hydrogen as naph- 

 thalin did, they named it Paranaphthalin. Afterwards Laurent changed its name 

 to Anthracene, by which it is still known. Fritzsche, in 1857, probably obtained the 

 same body, but gave it the formula OnHj^. Anderson also met with it in his re- 

 searches, established its composition, and formed some derivatives from it. Limprich 

 in 1866 showed it could be formed synthetically by heating benzol chloride (C^H^Cl) 

 with water; and Berthelot has since proved that it is formed by the action of heat 

 on many hydrocarbons. This first step was then complete and most satisfactory : 

 from alizarin they had obtained its hydrocarbon ; and this hydrocarbon was a body 

 already known, and with such marked properties that it was easy to identify it. 

 But would the next requirement be fulfilled ? would it, like benzol and naphthalin, 

 yield a quinone P The experiment had not to be tried ; for when they found that 

 anthracene was the hydrocarbon formed, they recognized in a body already known 

 the quinone derivable from it. It had been prepared by Laurent by the action 

 of nitric acid on anthracene, and called by him Anthracenuse ; and the same 

 substance was also discovered by Anderson, and called by him Oxanthracene. The 

 composition of this body was proved by Anderson and Laurent to be 0,^ H^ 0^, and 

 thus bears the same relation to its "hydrocarbon anthracene that quinone and 

 naphthaquinone do to their hydrocarbons. Graebe gave to it the systematic name of 

 Anthraquinone. 



We have, then, now three hydrocarbons (CgHg, Ck,!!^, and Ci^H,„) differing by 

 C4 Hj, and all forming starting-points for these different quinone series. Anthra- 

 quinone, acted upon by chlorine, gave substitution-products such as might have 

 been foretold. It is an exceedingly stable compound, not acted upon even by 

 fusion with potassic hydrate. Bromine does not act upon it in the cold ; but at 

 100° it forms a bibromanthraquinone. Other bromine compounds have also been 

 formed. 



Now, if the analogies which have guided them so far still hold good, they would 

 seem to have the means of forming alizarin artificially. Their theory is that it is 



dioxyanthraquinone ( C^ Ilg !'tt'({n ) , and if so, judging from what is known to take 



place with other quinone derivatives, should be formed from this dibromanthra- 

 quinone on boiling it with potash or soda and then acidulating the solution. They 

 try the experiment, and describe how, contrary at first to their expectation, on boil- 

 ing dibromanthraquinone with potash no change occurred ; but afterwards, on 

 using stronger potash and a higher temperature, they had the satisfaction of seeing 

 the liquid little by little become of a violet colour. This shows the formation of 

 alizarin. Afterwards, on acidifying this solution, the alizarin separated out in 

 yellowish flocks. On volatilizing it they get it in crystals like those obtained 

 from madder; on oxidizing it with nitric acid, they get phthalic acid; and 

 on precipitating it with the ordinary mordants or other metallic solutions, they 

 get compounds exactly comparable to those from the natural product. Every trial 

 confirms their success ; so, by following purely theoretical considerations, they have 

 been led to the discovery of the means of artificially forming this important organic 

 colouring-matter. A special interest must always attach itself to this discovery ; 

 for it is the first instance in which a natural organic colouring-matter has been built 

 up by artificial means. Now the chemist can compete with nature in its produc- 

 tion. Although the first, it is a safe prediction that it will not long be the only 

 one. Which colouring-matter will follow next it is impossible to say ; but, sooner 

 or later, that most interesting one, scientifically and practically, indigo, will have to 

 yield to the scientific chemist the history of its production. 



Returning for a moment to the percentage composition of alizarin, now that we 

 know its constitution, its formula is established; and on comparing it (Cj^H^O^) 

 with all the difterent formulae which have been proposed, we see that the one advo- 

 cated by Schunck was most nearly correct — in fact that it differs from it only by 

 two atoms of hydrogen. It is not without interest to note that the next most im- 



