i68 MICRO-SPECTROSCOPE AND P0LAR1SC0PE [CH. VI 



§ 231. Absorption Specttrum of Permanganate of Pot- 

 ash. — 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 the 

 full opening of the illuminator. 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. 136, 137). For strength of solution see § 229. 



§ 232. 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 under the microscope in 

 place of the permanganate, using the same objective, 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 § 224. 

 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 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 character- 

 istic 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 

 sulphide, such as is used for a reducing agent in chemical labora- 

 tories. Shake the bottle gently and then allow it to stand for ten 

 or fifteen minutes. Examine it and the two bands will have been 



