Chemical Science. 379 



12. Oxides of Mercury. — Mr. Donovan has, in his late expe- 

 riments on the compounds of mercury, given the following as 

 the only proportions he could obtain of the elements in the two 

 oxides ; though the experiments were frequently and carefully 

 repeated : 



Black oxide. Mercury 96.04 



Oxygen 3.96 



100.00 



Red oxide. Mercury 92.75 



Oxygen 7.25 



100.00 

 It is observed also, that mercury perhaps presents an excep- 

 tion to the general law, that the second dose of oxygen is re- 

 tained by a metal with less force than the first. If red oxide of 

 mercury, in grains, be exposed nearly to a red heat, it becomes 

 black ; but it is still peroxide, for if immersed in mercury, or 

 water, so as to exclude oxygen, it comes out, when cold, even a 

 brighter red than before. The red oxide bears a much higher 

 heat than the black. When black oxide is exposed to a mode- 

 rate heat, part is reduced, and part is raised to the state of per- 

 oxide ; which then bears even a low red heat unaltered. It is 

 true that light renders red oxide black ; but this is only in its 

 progress to the metallic state. All these facts appear to sup- 

 port the exception. — Thorn. Annals xiv. p. 246. 



13. Volatility of Oxide of Lead. — Dr. Thomson states the 

 volatility of this substance to be such, that it rises in a common 

 red heat. In the conversion of lead into litharge, and the 

 litharge into lead again, by the manufacturer, a loss of about 

 10 per cent, is suffered from this cause. 



14. New Acetate of Lead. — Dr. Thomson has published the 

 analysis of a new acetate of lead. It was obtained at the 

 manufactory of Charles Macintosh, esq., in Glasgow, in large 

 flat rhomboidal crystals. The crystals were white and trans- 

 lucent, and consisted of flat rhomboidal prisms, with angles of 



