48 Professor A. H. Church [Feb. 17, 



dissolves, even in the cold, not only a brown pigment associated with 

 turacoverdin, but ultimately the whole substance of the web. By 

 using a much weaker solution of alkali (1 part to a thousand of 

 water) a far better result is obtained. [The characteristic absorption 

 band of turacoverdin, which lies on the less refrangible side of D, 

 was shown ; also the absorption bands of various preparations of 

 turacin.] I have refrained from the further investigation of 

 turacoverdin, hoping that Dr. Krukenberg would complete his 

 study of it. At present I can only exj>ress my opinion that it is 

 identical with the green pigment into which turacin when moist is 

 converted by long exposure to the air or by ebullition with soda, and 

 which seems to be present in traces in all preparations of isolated 

 turacin however carefully prepared. 



A few observations may now be introduced on the physical and 

 chemical characters of turacin. It is a colloid of colloids. And it 

 enjoys in a high degree one of the peculiar properties of colloids, that 

 of retaining, when freshly precipitated, an immense proportion of 

 water. Consequently, when its solution in ammonia is precipitated 

 by an acid, the coagulum formed is very voluminous. [The experi- 

 ment was shown.] One gram of turacin is capable of forming a 

 semi-solid mass with 600 grams of water. Another character which 

 turacin shares with many other colloids is its solubility in pure 

 water and its insolubility in the presence of mere traces of saline 

 matter. It would be tedious to enumerate all the observed properties 

 of turacin, but its deportment on being heated and the action of 

 sulphuric acid upon it demand particular attention. 



At 100° C, and at considerably higher temperatures, turacin 

 suffers no change. When, however, it is heated to the boiling-point 

 of mercury it is wholly altered. No vapours are evolved, but the 

 substance becomes black and is no longer soluble in alkaline liquids, 

 nor, when still more strongly heated afterwards, can it be made to 

 yield the purple vapours which unchanged turacin gives off under the 

 same circumstances. This peculiarity of turacin caused great 

 difficulty in its analysis, for these purple vapours contain an 

 organic crystalline compound in which both nitrogen and copper are 

 present, and which resist further decomposition by heat. [Turacin 

 was so heated as to show its purple vapours, and also the green flame 

 with which they burn.] This production of a volatile organic com- 

 pound of copper is perhaps comparable with the formation of nickel- 

 and ferro-carbonyl. 



The action of concentrated sulphuric acid upon turacin presents 

 some remarkable features. The pigment dissolves with a fine crimson 

 colour, and yields a new compound, the spectrum of which presents a 

 very close resemblance to that of hasmatoporphyrin [Turacin was 

 dissolved in oil of vitriol : the spectrum of an ammoniacal solution of 

 the turacoporphyrin thus produced was also shown], the product 

 obtained by the same treatment from hasmatin : in other respects also this 

 new derivative of turacin, which I call turacoporphyrin, reminds one 



