PORPHYRINS 



15 



The feathers of Turaco, when placed in the path of a beam of light, 

 show two well-marked absorption bands in the green portion of the 

 spectrum. Possibly there is also another band, which is at best a 

 very indistinct one, and as it may not be due to turacin we will 

 disregard it, confining our attention to the obvious ones. These we 

 will call a and ^8, the former having its position of maximum density 

 at about 5830 Angstrom units and the latter at about 5420 a.xj. When 

 the pigment is dissolved in, say, "4 per cent, ammonia, the general 

 character of the bands remains the same, but their positions alter. 

 Each band shifts towards the blue end of the spectrum so that their 

 new positions are a = 5625 and jS = 5260 a.u. It is not necessary 

 that the turacin should be in the feathers however to give the former 



590 585 580 575 570 565 560 555 550 545 540 535 530 525 520 



J I I I I I I ' _ I I L 



OL 



turacin In feather 



L^ N H5 soLution of turacin precipitated 2 

 by acid lo 



goJ 



turacin In add gum arable 



d turacin In 0*4% Ammonia S 



i3 



^ turacin xn acid, solut.of acetone 

 or alcohol. 



^i3 



oi. 



a;. 



turacin vn acid acetone 2 

 beginning to precipitate S 



/3,+/32 



590 585 580 575 570 565 560 555 550 545 540 535 530 525 520 

 Fia. 2. Positions of the absorption bands of turacin under various conditions. 



type of spectrum, for if the alkaline solution be rendered acid the 

 bands revert to their original position, or very nearly so. Nor is it 

 necessary that the turacin should be dissolved in alkali in order to 

 give the second type of spectrum. (Following Keilin we shaU call 

 the type of spectrum, which is approximately that of the feathers, 

 type A, and that which is scarcely distinguishable from that of the 

 alkaline solution, type B.) Type B may be obtained by dissolving 

 turacin in acid alcohol, or in acid acetone. Indeed, according to 

 Keilin, if the pigment be in true solution, whatever the solvent, type B 

 is obtained, while type A appears only when the turacin is present 

 in the form of a suspension. Thus the addition of acid to an alkaline 

 solution of turacin precipitates the pigment at the same time that 

 it alters the spectrum from type B to type A. There is a means, 



