149 
Aurin therefore appears to be the lower homologue of 
rosolic acid ; like the latter, it readily forms a tetrabromo- 
compound, which we obtained pure by the following process. 
Pure aurin was dissolved in hot glacial acetic acid, and this 
solution poured into a mixture of an excess of bromine and 
acetic acid. The liquid remained perfectly clear, but on 
standing for a few days the tetrabromaurin crystallised out 
almost completely. It forms small brownish green crystals, 
with a metallic lustre, which dissolve in alkalis with a 
purple colour. The determination of the bromine gave 
numbers agreeing closely with those required for the formula 
C 19 H 10 Br 4 O 3 
Whilst this investigation was going on a new light was 
thrown on the subject by the researches of E. and 0. Fischer. 
In order to elucidate the constitution of rosaniline these 
chemists endeavoured to convert rosaniline into the hydro- 
carbon from which it is derived. In this they did not suc- 
ceed, but they were able to transform leucaniline C 20 H 2 iN 3 , 
which stands to rosaniline in the same relation as leucaurin 
to aurin, into a hydrocarbon C 20 H 18 , which is the mother 
substance of this base, and from which it follows that the 
hydrocarbon corresponding to rosaniline has the composition 
C 20 H 16 , which also confirms the correctness of Hofmann’s 
formula for rosaniline. The leucaniline, which they em- 
ployed was obtained from commercial rosaniline; but 
Rosenstiehl has shown that this body, which is prepared by 
oxidising a mixture of aniline, solid paratoluidine and liquid 
pseudotoluidine, contains several, probably isomeric, bases. 
E. and 0. Fischer therefore in continuing their research* 
prepared one of them in the pure state by using a mixture 
of pure aniline and pure paratoluidine. The product was 
converted into the leuco-compound, from which, to their 
surprise, they obtained, not as before, the hydrocarbon C 2 o 
H 18 , but one having the composition C 19 H 16 or the lower 
^ Ber. Deutsch.. Chem. Ges.> XI. 195. 
