CHAPTER XII. 



THE OPTICAL PROPERTIES OF BLOOD. USE OF THE 

 SPECTROSCOPE AND OTHER INSTRUMENTS. 



Solutions of hemoglobin and the various modifications and 

 derivatives described in the last chapter absorb light from 

 certain regions of the spectrum. The character and extent 

 of this absorption are such as to afford a ready means of iden- 

 tifying blood or its pigments through the aid of the spec- 

 troscope. 



THE SPECTRUM FIELD. 



The absorption spectra with which we are here concerned 

 are all found in the middle portions of the spectrum between 

 the Fraunhofer lines C and F, that is in a region easily ob- 

 served. For practical purposes an elaborate instrument is not 

 necessary. Excellent service is rendered by many of the 

 smaller direct vision spectroscopes. For quantitative tests, 

 however, much more complete apparatus is required. The 

 blood spectrum differs from that of all other red solutions and 

 is very easily recognized with a little practice. As the absorp- 

 tive power of hemoglobin is very great dilute solutions only 

 are used and these must be observed in a rather shallow cell, 

 preferably in one with parallel sides about i centimeter apart. 

 For illumination a good oil lamp flame is excellent; a steady 

 gas flame may also be employed. 



The general arrangement of the essential parts of the spectroscope are 

 shown by the following figures. Fig. 12 illustrates, diagrammatically, the 

 path of the light rays through the instrument. From the source F the 

 light enters the collimator tube through a narrow slit and reaches the 

 prism P, where it suffers refraction and dispersion. Beyond the prism 

 the rays are received by the double convex lens of the ocular tube and 

 thrown to the eyepiece at E. A magnified virtual image is formed as 

 shown by the dotted lines. The third tube carries a scale, the image of 

 which is reflected into the ocular and shows with the spectrum. In absorp- 

 tion spectrum analysis, with which we are concerned here, the light at F 



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