116 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



The large form of spectroscope (fig. 32) consists of a tube A, called 

 the collimator, with a slit at the end S, and a convex lens at the end L. 

 The latter makes the rays of light passing through the slit from the 

 source of light parallel : they fall on the prism P, and then the 

 spectrum so formed is focussed by the telescope T. 



FIG. 32. Diagram of spectroscope. 



The third tube, D, seen in the next figure (fig. 33) carries a small 

 transparent scale of wave-lengths, so that the position of any 

 point in the spectrum may be given in terms of the corresponding 

 wave-lengths. 



FiG- 33. Spectroscope: A, collimator with adjustable slit at one (left) end and colli mating leiis at 

 the Other (right) eml ; B, tdeeoope moving on graduated are divided into drives: C, prism or 

 combination of prisms; D, tube for scale; I'!, mirror for Illuminating scale; F, vessel with 

 parallel glass sides for holdiny fluid, shown with the Hat: side towards the reader ; I, long 

 spectroscope bottle for examining a dee]) layer of fluid , H, Argiuul burner ; G, condenser for 

 concentrating the light from H on the slit, (From a photograph taken by Dr. Mac Man n for 

 .McK end rick's ' 1'hysiology.') 



If we now interpose between the source of light and the slit S 

 a piece of coloured glass (H in fig. 32), or a solution of a coloured 



