283 
It is however noteworthy that haemopyrroline forms so easily 
even in acid solutions diazocompounds and it is not improbable that 
this facility is in some manner connected with the constitution of 
the substance. An investigation of the behaviour of known bisubs- 
tituted homoloques of haemopyrroline towards diazoniumeompounds 
under similar conditions would prove highly interesting. 
The optical properties of haemopyrroline- disazo -dibenzene are 
not particularly interesting. The solutions in neutral solvents cause 
in the spectrum two bands, corresponding to the following wave 
lengths: 
Band 1, A 551 — 4 532 
Band 2.7 517-4 49. 
The hydrochloride of haemopyrroline - disazo - dibenzene, dissol- 
ved in alcohol causes only one band which is not well defined 
and situated on the thallium line. 
In the ultraviolet part of the speetrum no bands were found 
by applying the photographie method. 
It is of some interest that haemopyrroline-disazo-dibenzene is able 
to form compounds with certain metals, for instance with zinc. Zine- 
acetate, dissolved in alcohol of 50°/, concentration, added to an 
alcoholie solution of the azocolour causes a change in the coloura- 
tion; the previous bright red colour is surplanted by a violet blue, 
and the original spectrum also undergoes a characteristie change. 
There are now twc bands, corresponding to the following wave 
lengths: 1. 2 607 — 2— 577; 2. 2 563 — 4 538. 
Similar compounds are formed by haematoporphyrin, phyllopor- 
phyrin and mezoporphyrin; they have a different speetrum from 
that characterising the alkaline solution of the substances named 
and it is therefore quite justifiable to suppose that the constitutions 
of the two kinds of metalic salts are not alike, a view which is 
further supported by the fact that bimethylhaematoporphyrin, which 
does not contain any free hydroxylgroups is still able to form di- 
stinct compounds with zinc or copper salts. These compounds must 
therefore be caused by the presenee of an imide group in the sub- 
stance named, and the fact that haemopyrroline - disazo - dibenzene 
also forms similar metalie compounds supplies an additionary sup- 
port for this view. 
The erystals with the melting point 233° are not the only pro- 
