660 MERCURY. 



two compounds, of which, one crystallises in tetrahedrons, like 

 the chloride of calcium salt. Chloride of manganese forms a 

 compound in good crystals, Mn Cl + Hg C1 + 4HO. Chlo- 

 rides of iron and zinc form similar isomorphous salts, Fe C1 + 

 Hg Cl + HO, and Zn Cl+Hg Cl + HO. The double chlorides 

 of zinc and of manganese are remarkable in one respect, 

 that chloride of mercury dissolved by them in excess, crystallizes 

 by evaporation in fine large crystals, such as cannot be obtained 

 in any other way. Chlorides of cobalt, nickel and copper form 

 similar crytallizable salts ; but chloride of lead, on the contrary, 

 does not appear to form a double salt with chloride of mercury 

 (Bonsdorff). 



Bromide of mercury, Hg Br, 2244.1 or 179.82. This salt is 

 obtained by treating mercury with water and bromine. It is 

 colourless, soluble in water and alcohol, and when heated, fuses 

 and sublimes, exhibiting a great analogy to chloride of mercury 

 in its properties. Its density in the state of vapour is 12,370. 

 Bromide of mercury forms a similar compound with sulphuret 

 of mercury Hg Br + 2Hg S, which is yellowish. It was also 

 combined, by Bonsdorff, with a variety of alkaline and earthy 

 bromides. Bromide of mercury combines with half an equiva- 

 lent of ammonia, in the dry way, and also gives a white precipi- 

 tate, with solution of ammonia, analogous to that derived from 

 chloride of mercury. 



Iodide of mercury, Hg I, 2845.3 or 228. It falls as a pre- 

 cipitate of a fine scarlet colour, when iodide of potassium is 

 added to a solution of chloride of mercury. It may also be 

 obtained by triturating its constituents together, in the proper 

 proportion, with a few drops of alcohol. To procure it in 

 crystals, M. Mitscherlich dissolves iodide of mercury to satura- 

 tion, in a hot concentrated solution of the iodide of potassium 

 and mercury, and allows the solution to cool gradually. When 

 heated moderately, iodide of mercury becomes yellow; at a 

 higher temperature it fuses and sublimes, condensing in rhom- 

 boidal plates of a fine yellow colour. The forms of the red and 

 yellow crystals are totally different, so that the change of colour 

 is due to the dimorphism of iodide of mercury. The yellow 

 crystals generally return gradually into the red state, when cold, 

 and this change may be determined at once by scratching the 

 surface of a crystal, or by crushing it. The density of iodide of 

 mercury in the state of vapour, is 15,680; it is the heaviest of 



