The Absorption Coefficient of Solution for Monochromatic Radiation. 13 



The arrangement of the apparatus is shown in figure 1. The light 

 from a Nernst glower g, operated at 110 volts on 0.8-ampere direct 

 current from a constant potential storage battery, was rendered 

 parallel by a lens Zi, 3.8 cm. in diameter and with a focal length of 

 20 cm. The light after passing through cell K' was focussed on the slit 

 A of the spectrograph by a second lens Z 2 , 3.8 cm. in diameter and with 

 a focal length of 20 cm. A shutter s was placed between the glower g 

 and lens Zi, by means of which the light could be turned on and off. 



The optical system thus far described, con- 

 sisting of the glower, the two lenses Zi and Z 2 , 

 and the cells, was held by a solid metal frame- 

 work and was perpendicular to the plane of the 

 drawing in figure 1. The light after passing 

 through lens Z 2 was reflected onto slit A by a 

 right-angle glass prism (not shown in figure 1) 



close to slit A. 



The temperature of the 

 K ' solution was recorded by a 



thermometer not placed in 

 - - f -^ the solution but fastened on 

 the metal frame supporting 

 the cells. 



The spectrograph con- 

 sisted of the Littrow mount- 

 ing of a plane grating. The 

 grating had a ruled area 6 cm. by 7.5 cm. and 

 was ruled 15,000 lines to the inch. The cone 

 of light from slit A was reflected by a right- 

 angle glass prism through the large achromatic 

 lens Z 3 , 10 cm. in diameter and with a focal 

 length of 75 cm. The spectrum was brought 

 to a focus at slit B. The grating possessed a 

 bright first-order, and this first-order spectrum 

 FIG. i. Schematic diagram was used throughout the present work. The 

 dispersion was such that with slit B 1 mm. 



wide a beam of light containing a wave-length range of 20 A. or 2juju 

 passed through. In this work both slit A and slit B were always 1 

 mm. in width. The grating was mounted on a turntable, which was 

 rotated from the outside by a worm-screw, thus causing various wave- 

 lengths to pass through slit B. The approximately monochromatic beam 

 of light from slit B was focussed on the junction of the radiomicrometer 

 r by a lens Z 4 , 3.5 cm. in diameter and with a focal length of 6 cm. 

 K A complete description of the construction of the radiomicrometer is 

 given in Shaeffer's paper. 1 To eliminate the drift of the zero-point 



Carnegie Inst. Wash. Pub. No. 230, p. 44. 



