396 MARION I. NEWBIGIN. 



respectively bouellidin and acidobouellin. Now Professor 

 Lankester has shown that the solution which Krukenberg 

 regarded as that of neutral bonellin was in reality alkaline 

 bonellin, the neutral solution being not green but dusky grey. 

 We are thus entitled to omit Krukenberg^s first stage from 

 our comparison with chsetopteriu, and consider only his 

 bonellidin and acidobonellin solutions. We have already 

 described the colours of these solutions, and as the pigments 

 were not isolated there remains only the spectroscopic 

 characters. It is not necessary at present to discuss these in 

 detail, for an account of the alteration in position undergone 

 by the dominant band in the red is sufficient for our purpose. 

 Bonellin, like chsetopterin, exhibits in neutral solution a very 

 strong band in the red. On the addition of acid this band, 

 without marked diminution in intensity, shifts its position 

 towards the right. This is an old observation, Krukenberg 

 found, however, that a further addition of acid in very large 

 excess caused the band to move back until it almost occupied 

 its original position. It was this double movement, com- 

 bined with the colour changes in his solutions, which induced 

 him to reject Sorby's suggestion that the acid has merely a 

 physical effect, and to put forward the theory of the existence 

 of two acid compounds. The subject has not apparently been 

 again studied. 



Passing from solutions of bonellin to those of chsetopterin, 

 we find that here again acid has a duplex effect. While a 

 small amount of acid produces the blue colour already described 

 by Professor Lankester, I find that a very large excess turns 

 the blue solution a pure clear green, with diminished fluores- 

 cence. Further, an examination of the spectra shows that, as 

 in bonellin, the band in the red shifts first to the right, then 

 with excess of acid back to its original position. The band of 

 chsetopterin does not occupy exactly the same position as that 

 of bonellin, nor is the movement so extensive, but there is at 

 least an analogy. 



Characters of Acidified Solutions. — The question 

 whether the changes which occur on the successive addition 



