408 MARlOiN' 1. NEVV131GIN. 



ill ether or alcohol. If the precipitate is treated vvitli a little 

 dilute acid the colour chaiiges_, and, after washing with water, 

 the pigment can be dissolved in ether or alcohol. The alco- 

 holic solution is blue-green in colour, but the blue is not 

 intensified by acid, and spectroscopic examination shows that 

 the solution consists of a mixture of unaltered chsetopterin 

 and the green acid derivative already described. The colour 

 and fluorescence vary according to the amount of the deriva- 

 tive present, and this depends upon the amount of acid 

 employed to decompose the compound. If a considerable 

 amount of the derivative is present the fluorescence becomes 

 indistinct, and an ajjpreciable amount of a brown insoluble 

 residue remains behind when the acidified precipitate is treated 

 with methylated spirit. These results show that precipitation 

 with lead acetate cannot be readily employed as a means of 

 purifying chsetopterin, for when the insoluble lead compound 

 is treated with acid a portion of chsetopterin as it is set free is 

 converted into the green acid derivative (cf. the efi'ect of acid 

 on the ammonia compound as noted above, p. 406) ; other salts 

 give similar results. 



The solution obtained in methylated spirit from the acidi- 

 fied precipitate after lead acetate is of a singularly pure and 

 beautiful blue-green colour, and rarely gives more than one 

 definite band, though the band in the yellow may be repre- 

 sented by a shading. The band at C has its apparent centre 

 about X 654) (cf. the first band of fig. 2), but it is of course 

 really the result of the apposition of the band of chectopterin 

 and that of the green derivative. Before the relation of chse- 

 topterin to acids was fully understood this solution was 

 thought to contain a single pigment, and a considerable quan- 

 tity of the dried pigment was tested for nitrogen by igniting 

 with metallic sodium. The test showed the presence of 

 nitrogen, but, as the pigment was a mixture of the acid deri- 

 vative and original chsetopterin, the result is only to show that 

 chsetopterin itself contains nitrogen. In this respect it resem- 

 bles bonellin. It would be of interest to know whether, when 

 chsetopterin splits into the green acid derivative and the brown 



