60 MICRO-SPECTROSCOPE AND POLAR/SCOPE. 



MICRO-SPECTROSCOPE — EXPERIMENTS. 



§ 144. Put the micro -spectroscope in position, arrange the slit and 

 the Amici prism so that the spectrum shall show the various spectral 

 colors going directly across it (§§ 133-135) and carefully focus the slit. 

 This may be done either by swinging the prism-tube aside and pro- 

 ceeding as for the ocular micrometer (§ 114) or by moving the eye-lens 

 of the ocular up and down while looking into the micro-spectro- 

 scope until 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 (§ 136). With the lever move the comparison 

 prism across half the field so that the two spectra shall be of about 

 equal width. 



§ 145. 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 18 mm. objective and use the full opening of the illumina- 

 tor. 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. 



§ 146. Absorption Spectrum of Blood. — Obtain blood from a re- 

 cently 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 in 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 advan- 

 tageous to determine the wave length opposite the center of the dark 

 bands. This may be done easily by setting the scale properly as de- 

 scribed in § 138. 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 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 elevate the vial and the effect of a thicker 



