106 ELEMENTARY CHEMICAL MICROSCOPY 



one for use with the microscope in a vertical position, the other 

 for a slightly inclined instrument. 



Since the prism forms an integral part of the eyepiece, changes 

 in magnification must be made wholly by changing objectives or 

 changing the distance from drawing board to prism. 



Microspectroscopes or Spectroscopic Oculars consist of direct 

 vision spectroscopes as integral parts of microscope eyepieces. 

 They are usually constructed after the Sorby-Browning pattern, 

 using a compound direct vision Amici prism. These prisms 

 consist of either three or five units, a prism of flint glass between 

 two of crown glass, or two prisms of flint glass alternating with 

 three of crown glass. This prism is mounted just above the eye 

 lens of the ocular, while the slit of the spectroscope is placed in 

 the plane of the diaphragm of the eyepiece. Usually a com- 

 paring prism is provided, which, when in position, cuts off half 

 the width of the spectrum and permits placing in juxtaposition 

 with the spectrum of the material being studied, the absorption 

 spectrum of a solution of known composition. The position of 

 bands or the amount of the spectrum cut off is determined by an 

 arbitrary scale; or by means of an Angstrom scale reading in 

 wave lengths, projected upon the spectrum, or by means of some 

 indicating device moving the length of the spectrum, its position 

 at any given point being indicated by a scale moved by a microm- 

 eter screw. This last type is the only one of value to the 

 chemist. 



The microspectroscope illustrated, 1 Figs. 54 and 55, is pro- 

 vided with a measuring device capable of yielding concordant 

 measurements with a very fair degree of accuracy. The instru- 

 ment consists of the cell or chamber K in which are housed the 

 slit 5, the comparing prism p, a movable diaphragm d, and in the 

 lower opening the field lens / of the ocular. A small opening O 

 in the side of K permits light, reflected by the mirror m, to enter 

 the prism p and thus yield a spectrum in juxtaposition to that 

 obtained from the object under the microscope. The solution 

 or transparent solid used for comparison is held before the open- 

 ing O by means of the clamps CC. The knob P serves to swing 



1 Manufactured by W. & H. Seibert, Wetzlar, Germany. 



