MI.M..II; XVIII.] THE CHLOR-IIYDROGEN PHOTOMETER. 



258 



TABLE III. 



Showing that the maximum for the photometer is in the indigo space of 



the spectrum. 



it may prove convenient to designate the precise ray to 

 which they apply. Perhaps the most simple mode is to 

 affix the name of the ray itself. Under that nomencla- 

 ture the instrument described in this paper would take 

 the name of indigo-photometer. 



There is no difficulty in adapting this instrument to 

 the determination of questions relating to absorption, 

 reflection, and transmission. Thus I found that a piece 

 of colorless French plate-glass transmitted 866 rays out 

 of 1000. 



Description of the Instru- 

 ment. First, of tlie Glass 

 Part. The chlor- hydrogen 

 photometer consists of a glass 

 tube bent into the form of a 

 siphon, in which chlorine and 

 hydrogen can be evolved 

 from hydrochloric acid con- 

 taining chlorine in solution 

 by the agency of a voltaic 

 current. It is represented by 

 Fig. 41, where a I c is a clear 

 and thin tube four tenths of 

 an inch in external diameter, 



Fig. 41. 



