H UI< . \ '/•: K'S S I '/■: CTROPHOXOMEl 'E R. 2 2 1 
Hiifner's spectrophotometer is an instrument of so much importance to the 
physiologist who intends to work al spectrophotometry, thai a short descrip- 
tion of the arrangements of its several parts appears desirable. 
The instrumenl as a whole, as well as the stand carrying the absorption- 
trough and the lamp, arc shown in Fig. 31. 
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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 2-1 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 Vierordt'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 
