78 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



less sharply defined absorption-band is seen occupying as 

 much space on the spectrum as the two bands of oxyhsemo- 

 globin, but the haemoglobin band is moved further to the left. 

 If this solution is shaken in the air the color returns to that 

 of oxyhsemoglobin and the latter's characteristic spectrum 

 also reappears. 



(c) Methcemoglobin. Add to blood (diluted 1:15) two 

 drops of a freshly prepared solution (10%) of potassium 

 ferricyanide. The color of the blood becomes brown. The 

 spectrum, in addition to two bands corresponding nearly to 

 those of oxy haemoglobin, which, however, are only faintly 

 seen, shows a band in the red near C. If to such a solution, 

 while still in position before the spectroscope, a drop or two 

 of Stokes' reagent is added, the characteristic absorption- 

 bands of oxyhasmoglobin appear for a second and are then 

 quickly replaced by those of haemoglobin. Shaking in the 

 air causes the latter to be reoxidized to oxyhsemoglobin with 

 the consequent spectral change. 



(d) Hcemochromogen (Reduced Hcematiti). To blood 

 (diluted 1 : 15) add two or three drops of strong NaOH and 

 warm gently until the color changes to a brownish green. 

 Then cool and add two drops of Stokes' reagent. Such a solu- 

 tion shows in the spectrum two very dark bands coinciding 

 apparently with those of oxyhaemoglobin ; upon careful 

 examination, however, it will be seen that green light appears 

 on the left of the left band and consequently both bands must 

 be moved further to the right than the oxyhsemoglobin ones. 



(e) Hcematoporphyrin (Iron-free Hcematiri). Place a few 

 c.c. of concentrated H 2 S0 4 in a test-tube and add a drop of 

 blood, mixing well. The color changes to wine-red, and spec- 

 troscopically the solution shows two bands on the opposite 

 side of the D line. The one to the left is narrower and 

 weaker, while that to the right is much more intense, 



