1889.] A. Fedlcv— Volatility of some of the Compounds of MeTcnry. 195 



the symptoms of mercury poisoning ai'e strongly manifested." If, 

 however, the solution of mercuric chloride contains hydrochloric acid 

 or apparently other acids also, the salt does not volatilize at all when 

 evaporated, and it would appear to be only when pure solutions are 

 evaporated that this volatilization takes place. 



The power which steam has of carrying forward vapours of other 

 bodies which under ordinary circumstances are fixed or difficultly-volatile 

 is well-known, and there is thus perhaps nothing very surpi-ising that the 

 vapour of a body which boils at 295° should be carried over by steam, 

 but the fact that the addition of an acid such as hydrochloric to the 

 solution renders the salt non-volatile with steam requires explanation. 

 The possible reason why the volatility then ceases may perhaps bo found 

 in the fact proved by A. Ditto* that hydrochloric acid has the power 

 of forming direct crystallizablo compounds with mercuric chloride such 

 as HgClj, 2H01 7HcjO, &c. The behaviour of mercuric chloride in solu- 

 tion in water in being volatile and in yielding mcrcurous chloride in 

 sunlight is thus almost pai'allcl to the behaviour now observed with 

 mercuric chloride in the solid state. 



The next mercuric salt examined was mercuric bromide, which was 

 placed in a sealed tube in vacuo with sodium hydrate in the upper part 

 of the tube. After exposure to sunlight for about a year it was found 

 that the end of the stick of sodium hydrate nearest the bromide for 

 a space of about an inch had become coated with an incrustation. The 

 incrustation was very thick at the end of the stick and of a dark grey 

 brown colour ; it was also tolerably thick over at least six- tenths of an 

 inch of the hydrate and the remaining part was thinner and of a brown 

 colour. This incrustation was examined and was found to consist 

 almost entirely of mercuric oxide, of which there was rather a largo 

 amount, but a few small globules of metallic mercury were also de- 

 tected. The mercuric bromide still in the tube was examined, and it 

 was found that only a very few needle-shaped crystals were left after 

 the mass was treated with boiling water. These needle-shaped crystals 

 were apparently mcrcurous bromide but the qiiantity examined was 

 small. 



The action of mercuric bromide in simlight and in vacuo is there- 

 fore almost parallel with that of mercuric chloride, but tho bromide is 

 sensibly less volatile at tho ordinary temperature of tho air than tho 

 chloride is. I have not been able to find any determination of the 

 melting and boiling point of the bromide, but it is known that the salt 

 can be sublimed, but at a higher temperature than tho chloride. 



* Compt. rpud. 92, 353-355. 



