146 MICRO-SPECTROSCOPE AND POLAR/SCOPE [CH. VI 



§ 209. Absorption Spectrum of Permanganate of Potash. — 

 Make a solution of permanganate of potash in water of such a strength 

 that a stratum 3 or 4 mm. thick is transparent. Put this solution in a 

 watch-glass with sloping sides, and put it under the microscope. Use 

 a 50 mm. or 16 mm. objective, and use the full opening of the illumi- 

 nator. Light strongly. Look into the spectroscope and slowly move 

 the watch-glass into the field. Note carefully the appearance with the 

 thin stratum of liquid at the edge and then as it gradually thickens on 

 moving the watch-glass still farther along. Count the absorption 

 bands and note particularly the red and blue ends. Compare carefully 

 with the comparison spectrum (Figs. 121, 122). For strength of solu- 

 tion see § 207. 



§ 210. Absorption Spectrum of Blood. — Obtain blood from a 

 recently killed animal, or flame a needle, and after it is cool prick the 

 finger two or three times in a small area, then wind a handkerchief or 

 a rubber tube around the base of the finger, and squeeze the finger 

 with the other hand. Some blood will ooze out of the pricks. Rinse this 

 off into a watch-glass partly filled with water. Continue to add the blood 

 until the water is quite red. Place the watch-glass of diluted blood un- 

 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 easily be done by setting the scale properly as described in § 202. 

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

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

 microscope. 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 much darker, and if the solution is thick enough 

 onfy 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. 

 Shake the bottle gentl} 7 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 



