FROZEN SOLUTIONS. 



181 



the solutions, even at 180, resembled in breadth and regular spacing 

 those of the solid salts at room temperature. The uranyl acetate in 

 alcohol proved to be the exception, since at 180 it resolved into 

 faint lines, which did not, however, coincide in position with those of 

 the solid acetate at that temperature. 



The variety of shifts with systematic dilution and temperature 

 change led to the second investigation, 1 in the hope that some general 

 law of shift might be deduced. It was also planned to study the funda- 

 mental relations between concentration and frequency interval, 

 temperature, and state of resolution, etc. With these relations in view 

 much work was done which led to the discovery of many beautiful 

 and unique spectra. 



EXPERIMENTAL METHOD. 



For the study of the spectra, except where otherwise specified, a 

 Hilger constant-deviation spectrometer was used. 



The apparatus for the cool- 

 ing and excitation of the sub- 

 stances under observation 

 was designed to enable the 

 observer to hold the tempera- 

 ture of the specimen con- 

 stant at any temperature 

 between and -180 C. 

 The mounting consisted of a 

 cylindrical copper block M 

 (fig. 90), the top of which 

 was bored to receive a small 

 test-tube F, which contained 

 the fluorescent solution. The 

 side of the block was 

 channeled to let the exciting 

 light fall on the specimen and 

 to let the fluorescent light 

 out. To the bottom of this 

 copper block was soldered a 

 cylinder of sheet copper, 

 which could be partially or 

 completely covered by the 

 liquid air in the unsilvered 

 Dewar bulb D, thus produc- 

 ing different temperatures in 

 the specimen. This mount- 

 ing was rigidly suspended 

 from above by partially non- 



FIG. 90. 



1 Howes. Physical Review (2), vol. 6, p. 193. 1915. 



