404 MARION I. NEWBIGIN. 



shows a double band in the red, the one to the right being 

 more distinct. The right-hand band is entirely new, the 

 other is one of the bands of chsetopterin. By successive 

 treatment with acid it is possible to remove the left-liand 

 baud from the ether almost entirely, and leave only the new 

 band at X 641, — that is the second band of fig. 3 ; the solution 

 is then pure green without fluorescence. 



The changes which chsetopterin undergoes on the addition 

 of acid I therefore explain as follows : 



When a small amount of acid is added to a neutral solution, 

 a small amount of a new pigment of a green colour is formed, 

 which shows one band with its centre at X 641. This band, 

 however, is so near the broad band of chsetopterin that the 

 two overlap, and in strong solution the apparent result is to 

 shift the red band to the left, as well as to produce that inde- 

 finiteness of margin of which we have already spoken (see 

 fig. 2). The other slight peculiarities of the spectrum of 

 acidified solutions I believe to be analogous to the changes 

 seen in the position of the bands of bonellin when the solvent 

 is varied, and not to indicate chemical change. 



When excess of acid is added to the solution the green 

 derivative is not destroyed, but, owing apparently to its imper- 

 fect solubility in strong acid, its band disappears, leaving 

 only the original chsetopterin band. This is, as I believe, the 

 explanation of that shifting of bands of which we have already 

 spoken (p. 396). The disappearance of the band of the deriva- 

 tive in strong acid solution is paralleled by that of the other 

 chsetopterin bands, which become exceedingly indistinct when 

 much acid is present in the solution, although by removal of 

 the acid the original pigment can be recovered. 



The changes which occur in the spectrum of chsetopterin 

 solutions when acidified I thus believe to be due to the blend- 

 ing of the spectrum of unaltered chsetopterin and that of an 

 acid derivative. The colour-change is, I believe, similarly due 

 to the mixture of pigments present. 



Characters of the Green Acid Derivative. — The 

 green derivative formed by the addition of acid to a solution 



