238 PHYSIOLOGICAL CHEMISTRY. 



With increasing dilution they grow fainter and are scarcely visible in solu- 

 tion No. 7. In all the solutions examined note the position of these bands 

 with reference to the characteristic colors. Note also that the bands grow 

 narrower with increasing dilution, and that it becomes more and more 

 difficult to locate the edges of the bands sharply. This fact has some 

 bearing on questions of quantitative determinations to be referred to later. 

 Some of the common absorption spectra are illustrated. 



With instruments furnished with a simple scale it soon be- 

 comes an easy matter to fix approximately the limits between 

 which each band is found and also the point of deepest absorp- 

 tion in each band. These data may be expressed in arbitrary 

 scale divisions, in fractions of the distance from D to E, or 

 most definitely, in wave lengths of light, if the instrument has 

 been graduated in that way. In all accurate comparisons of 

 spectra some such method of recording the observations must 

 be adopted. 



Spectrum of Reduced Hemoglobin. It was pointed out 

 in the last chapter that the spectrum of reduced hemoglobin 

 is very different from that of the ordinary oxyhemoglobin. 

 In place of two bands we have after reduction a single broad 

 band filling three-fourths of the space between D and E. This 

 is the simple effect observed with Stokes' solution. If am- 

 monium sulphide is employed in place of Stokes' solution the 

 same broad band appears and in addition a single narrow band, 

 the center of which is in the red to the left of D. This narrow 

 band may be due to some sulphohemoglobin formed at the 

 same time. It will be recalled that the reduced hemoglobin 

 solution is purplish red in place of deep bright red. 



Ex. To a dilute solution of blood, about I part to 50 of water, add a 

 few drops of strong ammonium sulphide solution and warm gently in a 

 test-tube until the change of color noted above is reached. Now place the 

 tube before the slit of the spectroscope and observe the bands referred 

 to, especially the narrow one in the red. Hydrogen sulphide gives prac- 

 tically the same result. 



Ex. Repeat the above experiment, using Stolces' solution instead of the 

 sulphide. A single broad band appears now ; if the liquid is shaken briskly 

 the air acts on the reduced coloring matter with oxidizing effect, as shown 

 by a division of the band, but only temporarily. On standing a short time 

 the single broad band, not very sharply defined, returns. For these tests 



