284 



CHEMISTRY. 



Fig. 105. 



the brightest light appearing in the centre of the yellow 



portion. By making 

 an opening of this 

 shape very narrow, 

 there is less overlap- 

 ping of the different 

 colors, and a purer 

 spectrum is obtained. 

 A very narrow open- 

 ing with parallel sides, 

 called a slit, is gener- 

 ally employed in ex- 

 amining the spectra of different bodies ; and in the case of 

 discontinuous or broken spectra, the colored image of the 

 slit is what produces the banded appearance of such spec- 

 tra. A narrow ray of yellow light produces a yellow 

 band of light in the spectrum, a red or a blue bundle of 

 rays produce a red or a blue line or band in the spectrum. 

 This is shown in Fig. 105. 



401. The Spectroscope. This is the name of the instru- 

 ment employed for thus analyzing the light emitted from 

 different sources. A brief description of Fig. 106 (p. 285) 

 will suffice. A spectroscope consists essentially of a prism, 

 a telescope, and a slit. In the figure before you the prism, 

 A, is placed on a plate of metal supported by a tripod, the 

 telescope is at B, and the slit is attached to the tube C, 

 which contains also a lens at the end next to the prism. 

 The substance to be examined, held on a platinum wire sup- 

 ported by the stand /*, is heated in the non- illuminating 

 flame of a Bunsen burner, I the cone, w, at the top of the 

 burner serving simply to steady the flame. The light 

 passes from the flame, /, through the slit at the end of the 

 tube C into this tube ; the rays are made parallel by the 

 lens in this tube before they fall upon the prism, A. The 



