[lubovich & pearen] INFRA-RED SPECTROSCOPY 209 



type and the galvanometer a Paschen model. By this method he was 

 able to locate a large number of infra-red lines hitherto unknown. 



A number of lines found by Randall with the thermopile have 

 been identified by F. M. Walters^ by photography. An Anderson 

 grating was employed for this work and Seed plates sensitized to long 

 waves by staining with Dicyanin. A sample of the metal to be 

 examined was inserted in a hole bored in one of two copper or graphite 

 terminals, between which the arc was maintained, the lower electrode 

 always being positive. The overlapping second and third orders were 

 screened out by a cell of potassium bichromate or a piece of Jena red 

 glass. The majority of the lines measured by Walters lie between 

 X 5000A and X 9000A. It has already been noted that the limits of 

 photography indicated by Meggers,^ Kiess,'' Merrill,^ and McLennan 

 and Shaver^ may be as high as X 11650A. As the only work attempted 

 up to this limit for the materials tin, lead, bismuth, zinc and antimony 

 has been done by Randall and as the work of Walters by the photo- 

 graphic method did not extend much beyond X 9000A, an attempt 

 was made by the writer to use the photographic method to confirm 

 Walter's results in the region below X 9000A, and Randall's results 

 in the spectral region above this limit. 



(2) Preliminary Experiments, with Mercury 



Before proceeding to photograph the spectra of metals some 

 experiments were carried out on the mercury spectrum in order to 

 gain familiarity with the technique of the various operations. The 

 grating spectrograph was set for the region X 8000A to X 11,000A, 

 and the width of slit used was one mm. 



The light used was obtained from a mercury arc lamp running on 

 the 110 D.C. circuit and bearing a current of about four amperes. 

 A Wratten Wainwright filter No. 22 was used to cut off the over- 

 lapping portions of higher orders. Ordinary rapid Seed plates 

 sensitized to infra-red waves by Dicyanin were used. The plates 

 were dyed according to the formula of Merrill,^*' the solution used 

 bçing as follows: 



Distilled Water 70 C.C. 



Ehtyl Alcohol 60 C.C. 



Dicyanin 3.5 C.C. 



Ammonia 4.5 C.C. 



"F. M. Walters, Bureau of Standards, No. 411, April, 1921. 

 •Meggers, Bureau of Standards, Vol. 14, p. 371, 1917. 

 ^Kiess, Bureau of Standards, No. 324, p. 637, 1918. 

 «Merrill, Bureau of Standards, No. 318, p. 487, 1918. 

 «McLennan and Shaver, Proc. Roy. Soc. A., Vol. 100, 1921. 

 "•Merrill, Bureau of Standards, No. 318, p. 487, 1918. 



U— C 



