TRANSACTIONS OF THE SECTIONS. 59 



and then into a dioxyanthraqiiinone, 



C,,He(HO),0„ 



now known as " isoanthraflavic acid" — a substance having the same compositioa 

 as alizarin, but being only an isomer of that body and possessing no affinity for 

 mordants ; like monoxyanthraquiuone, however, when further heated with alkali 

 it becomes oxidized and yields a colouring-matter, which is " anthrapm-pm-in," 



Ci,Hg (110)3 O,. 



Looking at these reactions, it appears rather remarkable that Graebe and 

 Liebermann should have succeeded in preparing alizarin from dibromanthraquinone. 

 It can only be explained on the assumption that the hydrogen atoms replaced in the 

 disulpho-acidare different in position from those replaced in the dibromanthraquinone; 

 and of course it is possible that a disulpho-acid isomeric with that now known may 

 be discovered that will yield alizarin as a first product on treatment with alkali. 



In the reaction which takes place when monoxyanthraquinone or isoanthraflavic 

 acid become oxidized and change into alizarin and anthrapurpurin nascent hydrogen 

 is formed ; and this causes a reverse action to take place — ordinary anthraquinone, 

 or its hydrogen derivative, being formed, and a loss of colouring-matter resulting. 

 A small amount of potassic chlorate is now used with the caustic alkali, just suffi- 

 cient to overcome the reducing action, which has resulted in an increased yield of 

 colouring-matter, the percentage obtained being now not very much below the 

 theoretical quantity. 



When the process for making commercial artificial alizarin by treating anthra- 

 quinone with sulphuric acid was first adopted, the product from that treatment was 

 a mixture of the mono- and disulpho-acids of anthraquinone. Consequently the 

 colouring-matter prepared in this manner was a mixture of alizarin and anthrapur- 

 purin ; and the reason why dichloranthracene, when used in place of anthraquinone, 

 yields a product very rich in anthrapurpurin, is on account of the readiness with 

 which it forms a disulpho-acid of dichloranthracene, which afterwards changes into 

 the disulpho-acid of anthraquinone. 



At first it was supposed by many that the quantity of coal-tar produced would 

 not yield a sufficient supply of anthracene for the manufacture of artificial alizarin. 

 Experience has, however, proved that this supposition was groundless, as now the 

 supply is greater than the demand. 



Moreover some very interesting experiments have lately been made, by which 

 anthraquinone and its deiivatives have been obtained without the use of anthracene. 

 The most interesting are those in which phthalic anhydride is employed with 

 benzolic derivatives; for example, this anhydride gives with hydroquinone a 

 colouring-matter having the same composition, as well as most of the other 

 properties of alizarin. It is called quinizarin. Baeyer and Caro have also obtained 

 from phthalic anhydride and phenol oxyanthraquinone ; and by using pyrocatechin 

 in place of phenol they got alizarin itself. 



Although these products have not been obtained in sufficient quantities by 

 these processes to be of any practical value, we do not know what further researcli 

 may do. Already one of the substances used is being prepared on the large scale for 

 the manufacture of that beautiful colouring-matter "eosine;" I refer to phthalic 

 anhydride. 



Now, with reference to the origin of the products which are used for the manvi- 

 facture of artificial alizarin, we find the first researches made in reference to 

 anthracene were by Dumas and Laurent in 1832 ; subsequently Laurent further 

 worked upon this subject, and obtained, by the oxidation of this hydrocarbon, a 

 substance which he called anthracenuse ; he also obtained dichloranthracene. Dr. 

 Anderson also made an investigation on anthracene and its compounds in 1863, and 

 assigned to it its correct formula ; he reexamined its oxidation-product, which 

 Laurent called anthracenuse, and named it oxyanthracene, the substance we now 

 know as anthraquinone. 



All tiiese substances were without any practical value until 18G8 ; but we now 

 find them of the greatest importance, and used daily in immense quantities. 



But to bring out more clearly the practical importance of these fruits of scientific 



