196 A. Pedler — VolaHlUy of some of the Compounds of Mercury. [No. 2, 



Very few of the mercurous compounds lend themselves to the 

 detection of whether they are volatile at the ordinary temperature of 

 the air or not, for it is known that many of them under the influence 

 of light or of sunlight decompose. This is the case with mercurous 

 oxide, iodide, &c. An attempt was, however, made to determine whether 

 calomel would be volatilized in vacuo in sunlight ; and, in the case of some 

 experiments conducted in a manner similar to that previously described, it 

 was shewn that a veiy small deposit of mercury was formed on the sticks 

 of caustic soda. On examining, however, the mercurous chloride re- 

 maining in the tube after being exposed for some months to sunlight, 

 it was found that the salt was of a grey instead of the original wliite 

 colour. On testing the calomel carefully no trace of mercui'ic chlorido 

 could bo detected, but free mercury was found in distinct quantities. 

 The decomposition which therefore had taken place under the influence 

 of sunlight was 



Hg3 Clo = 2Hg + C\. 



As mercury had been itself formed by the decomposition of the 

 mercurous chloride, and as it is well-known that morcur'y is volatile, tho 

 presence of the mercury on the caustic soda is a little ambiguous, but 

 fi'ora the manner in which the deposit took place, and from the similar 

 nature of tho action to that of mercuric chloride, which could bo 

 watched as the experiment went on, it appeared to be highly probr.blo 

 that the mercurous chloride itself was volatile in an exceedingly feeble 

 manner at tho temperatm'es experimented with. 



As in the above experiments no actual record of the temperatni'o 

 could be given day by day or hour by hour, it is perhaps desirable that 

 the general atmospheric temperatures during the experiments should be 

 stated. All the experiments were made in Calcutta, where the average 

 maximum monthly temperature during 1888 varied from 97° F. or 3(j° 

 C. in Juno to 74° F. or 23° 0. in January, while tho highest maximum air 

 temperature was 107'2° F or 40'7° 0. The average minimum daily tem- 

 poratiire on tho other hand varied from 80° F, or 27° 0. in Juno to 5.5° 

 F. or 13° 0. in December. The average monthly temperature of solar 

 radiation in Calcutta in 1888 also varied from about 152° F. or 67° 0. iu 

 May to 124° F. or 51° C. in January. 



The very decided volatility of mercury and of such of its com- 

 pounds as mercuric oxide, mercuric chlorido, mercuric bromide, and 

 perhaps even mercurous chloride in such a climate as Calcutta having 

 been proved, it remains to give a word of warning to all those who uso 

 those substances in any way. In India, in particular, mercuric chloride 

 is iised leather freely, for many of tho preparations which are largely 

 xised to preserve books from the attacks of insects contain mercuric 



