132 MICRO SPECTROSCOPE AND POLAR/SCOPE. \_CH. VI. 



der the microscope in place of the permanganate, using the same object- 

 ive, etc. Note carefully the spectrum. It would be advantageous to 

 determine the wave length opposite the center of the dark bands. This 

 may be done easily by setting the scale properly as described in § 193. 

 Make another preparation, but use a homoeopathic vial instead of a 

 watch-glass. Cork the vial and lay it down upon the stage of the mi- 

 croscope. Observe the spectrum. It will be like that in the watch- 

 glass. Remove the cork and look through the whole length of the vial. 

 The bands will be very 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 ele- 

 vate 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 fol- 

 lowing : 



Add to the vial of diluted blood a drop or two of ammonium sulphide, 

 such as is used for a reducing agent in chemical laboratories. 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 Examine it and the two bands will have been replaced by a single, less 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. Shake the vial vigorously and the color will 

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

 troscope and the two bands will be visible. After five or ten minutes 

 another examination will show but a single band. Incline the bottle so 

 ■that a very thin stratum may be examined. Note that the stratum of 

 liquid must be considerably thicker to show the absorption band than 

 was necessary to show the two bands in the first experiment. Further- 

 more, while the single band may be made quite black on thickening the 

 stratum, it will not separate into two bands with a thinner stratum. In 

 this experiment it is very instructive to have a second vial of fresh dilut- 

 ed blood, say that from the watch-glass, before the opening of the com- 

 parison prism. The two banded spectrum will then be in position to 

 be compared with the spectrum of the blood treated with the ammonium 

 sulphide. 



The two banded spectrum is of oxy-hemoglobin, or arterial blood, the 

 single banded spectrum is of hemoglobin (sometimes called reduced 

 hemoglobin) or venous blood, that is, the respiratory oxygen is present 

 in the two banded spectrum but absent from the single banded spectrum. 

 When the bottle was shaken the hemoglobin took up oxygen from the 

 air and became oxy-hemoglobin, as occurs in the lungs, but soon the 

 ammonium sulphide took away the respiratory oxygen, thus reducing 



