HUFNEKS SPECTROPHOTOMETER. 221 



Hiifner's spectrophotometer is an instrument of so much importance to the 

 physiologist who intends to work at spectrophotometry, that a short descrip- 

 tion of the arrangements of its several parts appears desirable. 



The instrument as a whole, as well as the stand carrying the absorption- 

 trough and the lamp, are shown in Fig. 31. 



FIG. 31. Hiifner's spectrophotometer, as made by Albrecht. 



The spectrophotometer, the stand for the trough, and the lamp, rest upon 

 the optical bench which forms the base for the whole. The position of the 

 spectrophotometer is constant ; the trough-stand and the lamp move along a 

 slide, and can be placed at any required distance. During the actual experi- 

 ment, the anterior edge of the trough is in close contact with the anterior part 

 of the collimator. The lamp (which in the models recently and at present 

 constructed is a gas lamp provided with an Auer incandescent burner) is 

 for actual work placed at a distance of 24 to 25 cms. from the distal end of the 

 collimator. The lamp is fitted with a positive lens the focus of which is 

 made to correspond with the brightest part of the flame, so that perfectly 

 parallel rays fall upon the absorption- trough. The latter is in all respects 

 similar to the one used in Yierordt's method. 



Turning our attention to the spectrophotometer, see Fig. 31, it is seen to be 

 composed of a three-footed stand, furnished with levelling screws, the stand 

 supporting the platform on which is fixed the dispersing prism, which is 

 enclosed in a metallic case. To the right is seen the collimator and to the left 

 the telescope. 



1. The collimator. This is furnished with a single slit formed by the 

 edges of two slides moving transversely, each of which possesses its own 

 micrometer screw, furnished with an accurately divided drum. This arrange- 

 ment enables a slit of a precisely known width to be obtained, and the slit can 

 be widened or narrowed symmetrically, so that its centre remains constant. 



Unlike ordinary spectroscopes, Hiifner's spectrophotometer has, fixed to the 



