TRANSACTIONS OF THE SECTIONS. 57 



It appears, then, that there must exist in the root two substances kept apart 

 during the life of the plant in some way of which we know nothing ; but as soon 

 as it dies they begin slowly to act on one another, developing thus the colouring- 

 matters in madder. 



Coincident with the appearance of Schunck's first paper was one by Debus on 

 the same subject. He looked upon alizarin as a true acid, and gave it the name of 

 lizaric acid ; but, as far as the composition of it was concerned, the percentage num- 

 bers he obtained agreed closely with those given by Schunck. One other investi- 

 gation concludes all that is important in the history of alizarin as obtained from 

 madder. This last investigation is of great interest ; it was by Julius Wolff and 

 Adolphe Strecker, and published in 1850. They confirm the results of others so far, 

 that there are in the madder-root two distinct colouring-substances, this important 

 one alizarin, and the other one purpurin. They prepare these colouring-matters 

 much in the same way that Schunck did, and very carefully purify and analyze 

 them. The formulse which they give for them differ, however, from Schunck's : for 

 alizarin they give the formula C^gtl^^Og, and for purpurin CjgHjjO,,; further, they 

 suggest that, by the process of fermentation, the former is converted into the latter ; 

 and they show that by oxidation they both yielded phthalic acid. Since the pub- 

 lication of this research, until the last year or two, this formula for alizarin has been 

 generally adopted by chemists ; and in most modern books we find it given as ex- 

 pressing the true composition of that body. It was not only the careful and 

 elaborate work which they devoted to the subject, but also the ingenious and 

 apparently well-foimded theory on the subject which carried conviction with it. 

 Laurent had shown, not many years before, that when naphthalin, that beautiful 

 and white crystalline substance obtained from coal-tar, was acted on by chlorine 

 and then treated vdth nitric acid, a body known as chloraaphthalic acid, and having 

 the composition CooHjoCljOg, was obtained; and on comparing this formula with the 

 one they had obtained for alizarin, Wolff and Strecker at once concluded that it 

 really was alizarin, only containing two atoms of chlorine in place of two of 

 hydrogen ; make this replacement, an operation generally easily performed, and 

 from naphthalin they had prepared alizarin. Further, this relationship between 

 chlornaphthalic acid and alizarin is borne out in many ways : it, like alizarin, has the 

 power of combining with different basic substances, has a yellow colour, is insolu- 

 ble in water, melts at about the same temperature, is volatile, and when acted on 

 by alkalies gives a strongly coloured solution. Taking, then, all these facts into con- 

 sideration, can we wonder that these chemists feel convinced that they have esta- 

 blished the composition of alizarin, and have shown the source from which it is 

 to be obtained artificially ? Apparently but one very simple step remains to crown 

 their work with success, that of replacing the chlorine by hydrogen. Melsenshad 

 only shortly before shown how this substitution could easily be made in the case of 

 chloracetic acid, by acting on it with potassium amalgam ; and Kolbe had used the 

 battery for the same purpos? : both these processes, and doubtless all others that the 

 authors can think of, are tried upon the chlornaphthalic acid ; but chlornaphthalic 

 acid it remains, and they are obliged to confess they are unable to make this sub- 

 stitution ; stiU they are strong in the belief that it is to be done and will be done, 

 and conclude the account of their researches by pointing out the great technical 

 advantage will be the getting alizarin from a worthless substance such as naphthalin. 

 One cannot help even now sympathizing with these chemists in their not being able 

 to confirm what they had really the strongest evidence for believing must prove to 

 be a great discovery. We now know, however, that had they succeeded in effect- 

 ing this svibstitution, or had they in any other way obtained this chlornaphthalic 

 acid without the chlorine, if I may so speak of it, which since their time has been 

 done by Martins and Griess, alizarin would not have been obtained ; but a body 

 having a remarkable parallelism in properties to it would have been. This body, like 

 alizarin, is of a yellowish colour, but slightly soluble in water, easily in alcohol and 

 in ether, is volatile, and on oxidation yields the same products ; it is, in fact, an 

 analogous body but belonging to another group. We also now know that the formula 



firoposed by Wolff and Strecker, and so long in use, is not the correct one. But 

 ittle more remains to be added with regard to the history of alizarin, as gathered 

 ro m the study of the natural substance. Schiitzeuberger and Paraf suggested 



