654 MERCURY. 



MERCURIC COMPOUNDS. 



Oxide of mercury (red oxide], Mercuric oxide, Hg O, 1365.8 or 

 109.43. This compound is formed by the oxidation of mer- 

 cury at a high temperature, as has already been described, or 

 by heating the nitrate of mercury till all the nitric acid is 

 expelled, and the mass, calcined almost to redness, no longer 

 emits vapours of nitric oxide. As prepared by the last process, 

 oxide of mercury forms a brilliant orange-red powder, crystallized 

 in plates, and having the density 11.074. It is very dark red at a 

 high temperature, but becomes paler as it cools. When reduced 

 to a fine powder it .becomes yellow, like litharge, without any 

 shade of red. It was found by Mr. Donovan to be soluble to 

 a small extent in water. If contaminated with nitric acid, it 

 gives off nitrous fumes when heated in a glass tube, and a yellow 

 sublimate of subnitrate also appears. This oxide is known in 

 pharmacy as red precipitate. The same substance is obtained 

 by precipitation, when a solution of corrosive sublimate is 

 mixed with an excess of caustic potash, as a dense powder of a 

 lemon-yellow colour. It is necessary to use the potash in excess, 

 otherwise a dark brown oxichJoride is formed. The precipitated 

 oxide parts with a little moisture, when gently heated, but does 

 not change in appearance. At a red heat, the oxide of mercury 

 is entirely volatilised in the form of oxygen and metallic mer- 

 cury. 



When water of ammonia is digested for several days upon pre- 

 cipitated oxide of mercury, the latter is converted into a yellow- 

 ish-white powder, which Dr. Kane considers as Hg, NH 2 -f 

 2Hg O+3HO, or a hydrated compound of amide and oxide of 

 mercury. 



Sulphuret of mercury, Cinnabar, HgS, 1467 or 117.55. 

 This is the common ore of mercury, and sometimes occurs 

 crystallized forming a beautiful vermilion. It is prepared arti- 

 ficially, by fusing one part of sulphur in a crucible, and adding 

 to it by degrees six or seven parts of mercury, stirring it after 

 each addition, and covering it to preserve it from contact of air, 

 when it inflames from the heat evolved in the combination. 

 The product is exposed to a sand bath heat, to expel the sul- 

 phur uncombined with mercury, and afterwards sublimed in 

 a glass matrass by a red heat. A brilliant red mass of a 

 crystalline structure is thus obtained, which when reduced to fine 



