260 



USING THE MICRO-SPECTROSCOPE 



[Ch. VIII 



and look through the whole length of the vial. The bands will be 

 much darker, and if the solution is thick enough only red and a little 

 orange will appear. Re-insert the cork and incline the vial so that 

 the light traverses a very thin layer, then gradually elevate the vial 

 and the effect of a thicker and thicker layer may be seen. Note 

 especially that the two characteristic bands unite and form one wide 

 band as the stratum of liquid thickens. Compare with the following: 

 Add to the vial of diluted blood a drop or two of ammonium sul- 

 phide, such as is used for a reducing agent in chemical laboratories. 



so SO 



Fig. 140. Absorption Spectrum of Arterial and of Venous Blood. 



(From Gamgee and McMunn). 



i Absorption of arterial blood, oxy-hemoglobin. There are two definite 

 bands between wave lengths 0.60/z and 0.50^, that is, in the yellow-green, 

 and the blue end of the spectrum is cut down markedly. 



2 Single dark band of venous blood, hemoglobin, in the yellow-green. 

 The blue end of the spectrum is less cut off than with arterial blood. 



A B C D E F G H Fixed lines of the solar spectrum .90, .80, .70, .60, .50, .40; 

 wave lengths in microns in the different regions. These spectra have the red 

 end at the left instead of to the right, as is now more usual (fig. 144-147). 



Shake the bottle gently and then allow it to stand for ten or fifteen 

 minutes. Examine it and the two bands will have been replaced by 

 a single, less clearly defined band in about the same position. The 

 blood will also appear somewhat purple. Remove the cork to 

 admit fresh air, then shake the vial vigorously, and the color will 

 change to the bright red of fresh blood. Examine it again with 

 the spectroscope and the two bands will be visible. After five or 

 ten minutes another examination will show but a single band. In- 

 cline the bottle so that a thin stratum may be examined. Note that 

 the stratum of liquid must be considerably thicker to show the absorp- 

 tion band than was necessarv to show the two bands in the first 



