of the Vapours of Inorganic Salts. 57 



Mercuric and Mercurous Chloride* 



Mercuric chloride is volatile even at ordinary tempera- 

 tures, and its vapour pressure increases rapidly with tem- 

 perature from 20'7 mm. at 200° C. to 370 7 mm. at 

 2.0° C. In the present experiments "10 gram o£ mercuric 

 chloride was placed in an evacuated quartz tube, and by 

 means of the gas equation it was calculated that the pressure 

 of the vapour was approximately 1*6 atmospheres at 1000° 0. 

 Visual observations and the examination of numerous 

 photographs taken at temperatures ranging from 20° C. to 

 1000° 0. showed that there were no well-defined bands in 

 the region X2500-X6700. On the other hand, there was 

 distinct evidence of a general absorption in the ultra-violet 

 which increased in intensity and spread towards the red end 

 of the spectrum with rise of temperature. At 900° C. no 

 light of shorter wave-length than X 3400 passed through the 

 vapour. 



Hercurous chloride sublimes at about 400° C, and its 

 vapour consists of a mixture of mercury and mercuric 

 chloride unless special care is taken to free the salt Irom 

 traces of moisture. About *09 gram of the salt was heated 

 to temperatures varying irom 400° 0. to 800° C, and the 

 absorptiou spectrum was photographed and also visually 

 examined. 



The photograph taken at 400° C. showed general absorp- 

 tion in the region X 2500-X, 2800, and this increased with 

 rise of temperature, so that at 800° C. the continuous spec- 

 trum of the carbon arc could not be photographed below 

 X 3200. 



As in the case of mercuric chloride, the observations 

 carried out both visually and photographically indicated that 

 the vapour at temperatures varying from 400° C.-800° C. 

 gave no well-defined absorption bands. In the experiments 

 described, no special care was taken to absolutely remove 

 all traces of moisture, and consequently the vapour probably 

 consisted of a mixture of mercury and mercuric chloride. 

 According to the experiments of Wood *, mercury shows an 

 absorption band at \2536 which widens unsymmetrically 

 towards the red over a range of 400 A.U. as the pressure 

 increases to several atmospheres. If a foreign gas is 

 present, the line widens symmetrically at first, and after- 

 wards unsymmetrically towards the red. 



In the experiments on mercurous chloride the presence of 

 the \ 2536 line would be difficult to detect, since the mercury 



* Astropbys. Journal, xxvi. pp. 41-45 (1907). 



