[lubovich & pearen] INFRA-RED SPECTROSCOPY 199 



The thermopile consisted of 10 junctions of bismuth silver, 

 joined by silver solder, and flattened out into rectangular plates at the 

 exposed junctions, which were blackened. The galvanometer used 

 was of the Paschen type/ The sensitivity of the instrument was 

 such that a deflection of 1 mm. on a scale at the distance of one metre 

 was produced by a current of 5X10"^" amperes. 



To avoid the variation produced by temperature changes, and 

 by stray air currents, the thermopile and slit were enclosed in a nickel- 

 plated metallic box shown at h. 



The whole spectrometer was enclosed in a wooden box lined with 

 absorbent cotton. The box had a window at Si covered by a shutter, 

 and a second window through which to read the wave-lengths on the 

 drum. 



During the experiment the slits S\ and 52 were 0.3 mm. wide. 



The lamp was supplied with direct current from the mains. 



To avoid errors due to the variation of voltage the lamp was 

 connected in series with a rheostat by means of which a constant 

 difference of potential, 115 volts, was kept at the binding posts of the 

 lamp. 



The cells which contained the solutions were made of glass 

 2.5 mm. thick, and had 5 mm. distance between the walls. 



Preliminary measurements of absorption of alcohol, through both 

 cells gave results coinciding within one per cent. During the experi- 

 ment the cells were always placed at the same point in front of the 

 slit Si. 



(4) Residts 



The absorption for alcoholic solutions of concentration 1:10000 

 of Dicyanin, Dicyanin A, Pinacyanol, Nigrosin SS Blue shade, and of 

 1:2000 of Alizarin Blue S was observed as described above. The 

 results of these investigations are shown graphically in Fig. 2-6. 

 Fig. 2 shows the absorption curve for Dicyanin. It shows that 

 Dicyanin has a strong absorption up to 0.8 /x . At 0.9 /x it reaches a 

 minimum, and then has nearly constant magnitude up to 2 yu except 

 for a small maximum at 1 .0 /z. 



Fig. 3 shows absorption for Dicyanin A. It follows from the 

 absorption curve that Dicyanin A has its maximum shifted to the 

 red side of the spectrum, and has a broader region of high absorption, 

 though in magnitude it does not reach 36 per cent., which is the 

 absorption of Dicyanin. These two facts coincide perfectly with 



^Paschen, Zeit. fur Instr. 13, 1. p. 13-17, 1893. 



