58 REPORT— 1873. 



doubling Wolff and Strecker's formula for alizarin ; and Bolley suggested the formula 

 CjjHjg 0,., which, owing to the uneven number of hydrogen atoms, was soon rejected. 

 If we compare our present knowledge of alizarin with what it was when these re- 

 searches on the natural product were completed, it is as light compared with 

 darkness ; and we may well ask, whence has come this influx of knowledge ? The 

 answer, I hope to show you, is undoubtedly that it has come from the careful and 

 accm-ate study of abstract chemistry. I know of no history in the whole of 

 chemistry which more strikingly illustrates how the prosecution of abstract science 

 lays the foundation for great practical improvements than the history of alizarin 

 does. 



My object now is, then, to show you, as shortly as I can, how by indirect means 

 the composition of alizarin was discovered, how it has been built up artificially, 

 and how it is superseding for manufacturing-pui"poses the long- used natural 

 product. 



To trace this historj' from its source we must go back to 1785, when an apothe- 

 cary of the name of Hofmann obtained the calcium salt of an acid called quinic acid 

 from Cinchona- bark. This acid is now known to be of common occurrence in plants; 

 it exists in the bilberry and in coffee, in holly-, ivy-, oak-, elm-, and ash-leaves, 

 and probably many other leaves. Liebig also prepared the calcium salt, and was 

 the iirst to give a complete analysis of it ; the formula he gave for it was Cjj H^^ O,^. 

 I5aup, on repeating Liebig's experiments, arrived at a somewhat different conclu- 

 sion, and gave the formula C,, il^o ^*io- ^^ 1835, at Liebig's suggestion to determine 

 which formula was correct, Alexander Wosla-ensky, from St. Petersburg, then a 

 student at Giessen, imdertook the further investigation of this subject, and esta- 

 blished the formula 0,^11,4 0,2, the one in fact now in use. In the course of this 

 investigation, which he carried further than merely settling the percentage composi- 

 tion of this acid, he describes what to us now is of most interest, a new substance 

 having peculiar and very marked properties. He says that when a salt of quinic 

 acid is burnt at a gentle heat he gets aqueous vapour, the vapour of formic acid, 

 and a deposit of golden needles, which are easily sublimed. Afterwards he describes 

 how this same golden substance may be obtained from any salt of quinic acid by 

 heating it with manganic dioxide and dilute sulphuric acid ; it then distils over, 

 condensing in golden-yellow needles on the sides of the receiver, and may be 

 rendered pure by resublimation. The composition of this body he finds to be 

 C3 IIj O, and namts it quinoyl, a name strongly objected to by Berzelius, as 

 conveying a wrong impression of the nature of the body ; he proposed in place of it 

 the name quinone, by which it is still known. Far as this body would seem to be 

 renx)ved from alizaiin, yet it is the study of its properties which led to the arti- 

 ficial production of alizarin. 



Some years afterwards Wcihler also examined the decomposition of quinic acid ; 

 he prepares again this quinone, and follows exactly the process described by 

 Woski-ensky : he states that, with regard to the properties of this remarkable body, 

 he has nothing particular to add ; however, he proposes a different formula for it, 

 and discovers and describes other bodies allied to it ; among these is hydroquinone, 

 Cg Hg O^. Laurent afterwards shows that the formula proposed by Wohler is incon- 

 sistent with his and Gerhardt's views, and by experiment confirms the former 

 formida for this bodj'. Although many other chemists devoted much attention to 

 this substance, still its real constitution and relation to other compounds re- 

 mained long unknown. Thus Wohler, Laurent, Hofmann, Stiideler, and Hesse all 

 had worked at it; and much experimental knowledge with regard to it had been 

 acquired. One important point iu its history was, first, the discovery of chloranil 

 by Erdniann in 1841, and then Hofmann showing that, by heating quinone with 

 potassic chlorate and hydrochloric acid, chloranil could "be obtained from it — 

 that, in fact, chloranil was quinone in which all the hydrogen had been replaced 

 by chlorine. Perhaps the most general impression among chemists was, that 

 in constitution it was a kind of aldehyde ; certainly its definite place among 

 chemical compounds was not knowTi. Kekul(5 suggests a rational formula for it ; 

 but it is to Carl Graebe that we owe oiu' knowledge of its true constitution. In 

 1868 he published a remarkable and very able paper on the quinone group of com- 

 pounds, and then first brought forward the view that quinone was a substitution- 



