Ch. VIII] USING THE MICRO-SPECTROSCOPE 259 



the dark lines of the solar spectrum are distinct. If they cannot 

 be made distinct by focusing the slit, then the light is too feeble or 

 the slit is too wide. With the lever move the comparison prism 

 across half the field so that the two spectra shall be of equal width. 

 For lighting, see § 407. 



§ 411a. If one does not possess a micro-spectroscope, quite satisfactory- 

 results may be obtained by using a microscope with a 16 to 12 mm. objective 

 and a pocket direct- vision spectroscope in place of the eye-piece. (Bleile, 

 Trans. Amer. Micr. Soc, 1900, p. 8.) 



§ 412. Absorption spectrum of permanganate of potash. — Make 

 a solution of permanganate of potash by putting a few crystals in a 

 watch glass of water. The solution should be of a strength that a 

 stratum of 3 to 4 mm. thickness will be transparent. Place the watch 

 glass under the microscope. Use a 16 mm. or lower objective and 

 open widely the condenser diaphragm; 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 with the comparison spectrum 

 (fig. 148). For strength of solution see § 410. 



§ 413. 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 handker- 

 chief 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 t la- 

 scale properly, as described in § 405. 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 microscope. Observe the 

 spectrum. It will be like that in the watch-glass. Remove the cork 



