CH. XXVI.] 



THE SPECTROSCOPE. 



433 



coloured plate (spectrum 2). There are two distinct absorption 

 bands between the D and E lines ; the one nearest to D (the a 

 band) is narrower, darker, and has better-defined edges than the 

 other (the ft band). As will be seen on looking at fig. 365, a 

 solution of oxy haemoglobin of concentration greater than 0^65 

 per cent, and less than 0*85 per cent, (examined in a cell of 

 the usual thickness of i centimetre) gives one thick band over- 

 lapping both D and E, and a stronger solution only lets the red 

 light through between C and D. A solution which gives the 

 two characteristic bands must therefore be a dilute one. The 

 one band (y band) of haemoglobin (spectrum 3) is not so well 



ABC 



Fig. 365. Graphic representations of the amount of absorption of light by solution of (I) 

 oxyheemoglobin, (1) of haemoglobin, of different strengths. The shading indicates 

 the amount of absorption of the spectrum ; the figures on the right border express 

 percentages. (Bollett.) 



defined as the a or ft bands. On dilution it fades rapidly, so that 

 in a solution of such strength that both bands of oxyhsemoglobin 

 would be quite distinct the single band of haemoglobin has dis- 

 appeared from view. The oxyhsemoglobin bands can be dis- 

 tinguished in a solution which contains only one part of the 

 pigment to 10,000 of water, and even in more dilute solutions 

 which seem to be colourless the a band is still visible. 



Haemoglobin and its compounds also show absorption bands in 

 the ultra-violet portion of the spectrum. This portion of the 

 spectrum is not visible to the eye, but can be rendered visible 

 by allowing the spectrum to fall on a fluorescent screen, or on a 

 sensitive photographic plate. In order to show absorption bands 

 in this part of the spectrum very dilute solutions of the pig- 

 ment must be used. 

 K.P. P v 



