46^ X. BILE PIGMENT FORMATION, ETC. 



Absorption spectrum. A solution of protoverdohemochrome in 

 dilute i)yridine or chloroform shows a typical three-banded spectrum. 

 In 20% pyridine the position of the bands is: 1,657 mM(emM = 19-6); 

 II, 530 niM (cmM = 9-8); III, 498 m/x (e^^M = 8.15). There is also a 

 weak and indistinct absorption band in the ultraviolet at 350 mju, 

 while the Soret band is absent (1324) ■ In the absence of alkali, 

 dithionite does not alter the spectrum. 



Valericij of the iron. The solution of the problem as to whether the com- 

 pound is ferrous (a hemochrome) or ferric (a hem (chrome) met unexpected 

 difficulties {168S), which do not yet permit a clear decision. In neutral 

 pyridine solution evidently only one form is stable. The following experiments 

 are in favor of its being a hemochrome : 



(a) If ferricyanide is added to the neutral pyridine solution, the typical 

 bands disappear and are replaced by a diffuse absorption in the red; dithionite 

 restores the bands. 



(6) If verdohemochrome is treated with ammonia in the absence of 

 atmospheric oxygen, azahemochrome results {cf. below) without a reducer 

 being present. 



(c) If verdohemochrome is dissolved under coal gas in a mixture of 66% 

 acetic acid with a little pyridine, a carbon monoxide compound with an 

 absorption band at Oil mjU similar to that of carbon monoxide verdoheme 

 {cf. below) is observed. If more pyridine is added, the typical verdohemo- 

 chrome spectrum is restored. Previously the same experiment had been 

 carried out with the addition of some ascorbic acid {1712), but in the absence 

 of air this can be dispensed with. 



{d) In a weaker aqueous pyridine solution the absorption bands can be 

 made to disappear by shaking with air and can be restored by dithionite. 

 This can be expected, since the dissociability of hemichromes is usually 

 greater than that of hemochromes. 



On the other hand the following experiments indicate trivalent iron: 



{e) If dithionite is added to a pyridine solution of verdohemochrome made 

 alkaline with sodium hydroxide, the solution becomes yellow and the absorp- 

 tion bands disappear. If the solution is at once shaken with air the green 

 color and the spectrum are restored. If cyanide is added to the green alkaline 

 solution, dithionite does not alter its color. In the first paper of Lemberg 

 {1681), it had been reported that the reduction to a yellow compound could 

 only be observed with proto- and not with mesoverdohemochrome. This 

 was in error; evidently an. alkaline pyridine solution of the proto, and a 

 neutral one of the meso, compound had been studied. The explanation then 

 given, based on the assumption of a specific influence of the vinyl group, is 

 therefore not correct. The yellow reduction product has a rather high 

 absorption maximum at 455 m/Lt (emM = 57.5) which may be mistaken for 

 a Soret band. The experiments must be carried out with fresh solutions in 

 alkaline pyridine; on standing such solutions turn yellow without reducer, 

 and then turn green if dithionite is added. 



