ABSORPTION AND FLAME SPECTRA. 



[Every spectroscope ought to give two spectra, so that the position of any absorp- 

 tion band may be definitely ascertained. The spectroscope is fitted into the 

 ocular end of the tube of a microscope instead of the eye-piece. Small cells for 

 containing the fluid to be examined are made from short pieces of barometer-tubes 

 cemented to a plate of glass.] 



Fig. 10. 



Scheme of a spectroscope for observing the spectrum of blood A, tube ; S, slit ; 

 m m, layer of blood with flame in front of it ; P, prism ; M, scale ; B, eye of 

 observer looking through a telescope ; r i\ spectrum. 



Absorption Spectra. If a coloured medium (e.g., a solution of blood) 

 be placed between the slit and a source of light, all the rays of coloured 

 light do not pass through it some are absorbed ; many yellow rays are 

 absorbed by blood, hence that part of the spectrum appears dark to 

 the observer. On account of this absorption, such a spectrum is called 

 an " absorption spectrum" 



Flame Spectra. If mineral substances be burned on a platinum- 

 wire in a non-luminous flame (Bunsen's burner) in front of the slit, the 

 elements present in the mineral or ash give special coloured band or 

 bands, which have a definite position. Sodium gives a yellow, 

 potassium a red and a violet line. These substances are found in 

 burning the ashes of almost all organs. 



If sunlight be allowed to fall upon the slit, the spectrum shows 

 a large number of lines (Fraunliofer s lines) which occupy definite posi- 

 tions in the coloured spectrum. These lines are indicated by the 

 letters A, B, C, D, etc., a, b, c, etc. (Fig. 11). 



