OF ARTS AND SCIENCES. 35 



Investigations on Ligut and Ueat, fdblished with an appropriation feom tub 

 KuMFOBD Fund. 



11. 



CONTRIBUTIOX FROM THE PHYSICAL LABORATORY OF 

 HARVARD COLLEGE. 



ON THE SPECTRUM OF ARSENIC. 

 By Oliver W. Huxtington. 



Presented by Professor Trowbridge, June 28, 1881. 



It has been noticed in the case of the spectrum of nitrogen gas, that the 

 spectrum obtained from an electric discharge of low intensity through 

 a rarified atmosphere differs from that obtained when the intensity of 

 the discharge has been increased by a Leyden jar. In the case of the 

 low tension discharge, the bands of the spectrum appear fluted on the 

 more refrangible side ; but upon the introduction of a Leyden jar into 

 the circuit the fluted appearance at once vanishes, and the spectrum 

 breaks up into isolated bands. This diflference has been ascribed to a 

 difference of condensation of the molecule. Now as arsenic is allied 

 to nitrogen, it was thought the same difference might appear iu the 

 spectrum of arsenic, and we proposed to make this a subject of investi- 

 gation. For this purpose, we first prepared two tubes, — one an ordi- 

 nary Geisler tube, such as is used for showing the spectrum with 

 rarefied gas ; the other as shown in Fig. 1 of accompanying plate, for 

 the spark spectrum with Leyden jar. A small amount of pure metallic 

 arsenic was introduced into each tube, and they were then repeatedly 

 exhausted, each time replacing with hydrogen. After the final ex- 

 haustion, the tubes were heated, in order to fill them with the vapor 

 of arsenic. But, upon passing the spark through them, we could 

 obtain no definite or satisfactory result. The arsenic spectrum was 

 feeble, the hydrogen brilliant, and the fluted indefinite bands which 

 accompany the hydrogen spectrum wholly obscured the phenomenon. 



Judging from the statements in Roscoe's spectrum analysis that 

 these fluted portions of the hydrogen spectrum were accidental and 

 due to imjiurities, we attempted to get rid of them in order to bring 

 out the arsenic spectrum. "We, therefore, prepared several tubes with 

 pure hydrogen. We arranged tubes with two outlets, in order to pass 



