4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



observed wave lengths being consistent with grating measurements 

 within ±2 A. 



The thermocouple used is a modification of the type of single 

 junction vacuum thermocouple described by Brackett and McAlister.'^ 

 The source of continuous radiation is a tungsten ribbon filament, 

 using 16 amperes current at 6 volts and working at an approximate 

 temperature of 2900° K. 



INVESTIGATION OF LIQUID HYDROGEN CYANIDE 



In the present investigation, the absorption spectrum of hydrogen 

 cyanide in liquid phase has been studied with cell thicknesses of i mm., 

 I cm., 5 cm., and 30 cm. 



The liquid hydrogen cyanide was obtained through the courtesy of 

 W. B. Wood of the Plant Quarantine and Control Administration of 

 the Department of Agriculture. This product had quite a perceptible 

 odor of hydrogen sulfide. The original sample containing about 

 1500 cc. was distilled over P2O5, primarily to remove any water, but 

 a considerable quantity of sulfur was precipitated, as was expected 

 from the presence of hydrogen sulfide. The second 500 cc. fraction 

 was taken as an experimental sample. A drop of it did not affect 

 lead acetate paper. This purification was made possible through the 

 courtesy of Drs. G. E. Hilbert and L. B. Howard of the Fixed 

 Nitrogen Research Laboratory. 



Fig. 2. — Energy transmission curve sliowing absorption spectrum of 5 cm. 

 cell of liquid HCN at low dispersion. Slit width approx. 40A. 



Figure 2 shows the absorption of a 5 cm. cell in the region from 

 7/x to 2fx. The steadiness of the thermocouple will be ap]:)arent from the 

 smoothness of the record. This illustration shows the instrument set 

 for a relatively narrow spread, covering the entire region, and gives 

 a general idea of the relative intensities. Actual observations of wave 



' Rev. Sci. Instr., vol. i, p. 181, 1930. 



