178 METALS AND THEIR COMBINATIONS. 



soluble in 16 parts of cold and 2 parts of boiling water, in about 

 2 parts of alcohol, and in 4 parts of ether; when heated, it fuses 

 and is volatilized; it has an acrid, metallic taste, an acid re- 

 action, and strong poisonous properties. 



Mercurous iodide, Hydrargyrum iodidum viride, Hg 2 I 2 = 652.6 



(Green iodide or protiodide of mercury}. Both iodides of mercury 

 may be obtained either by rubbing together mercury and iodine 

 in the proportions represented by the respective atomic weights, 

 or by precipitation of soluble mercurous or mercuric salts by 

 potassium iodide. 



According to the U. S. P., mercurous iodide is made by 

 triturating 8 parts of mercury with 5 of iodine (and a little 

 alcohol) until all globules of mercurj r have disappeared and a 

 green powder has been formed, which is washed with alcohol in 

 order to eliminate small quantities of mercuric iodide which 

 may have been formed : 



2Hg + 21 = Hg 2 I 2 . 



The powder is finally collected and dried between paper at 

 a low temperature. During the whole operation light should 

 be excluded as much as possible, as it decomposes the com- 

 pound. 



Mercurous iodide is a dull green to greenish-yellow, tasteless 

 powder, insoluble in water, alcohol, and ether. It is easily de- 

 composed into mercuric iodide and mercury. 



Mercuric iodide, Hydrargyri iodidum rubrum, HgI 2 = 452.9 (Red 

 iodide or biniodide of mercury). Made by mixing solutions of 

 potassium iodide and mercuric chloride, when a yellow precipi- 

 tate is formed, turning red immediately : 



HgCl 2 + 2KI = 2KC1 + HgI 2 . 



Mercuric iodide is soluble both in solution of potassium 

 iodide and mercuric chloride, for which reason an excess of 

 either substance will cause a loss of the salt when prepared. It 

 is a scarlet-red, crystalline, tasteless powder, almost insoluble 

 in water and but slightly soluble in alcohol ; on heating or 

 subliming it turns yellow in consequence of a molecular change 



