406 M. C. Lea— Color Relations of ' 



telluride are colorless; also the oxygen acids of both are color- 

 less. There is little doubt, therefore, that selenium and tel- 

 lurium, like sulphur, have colorless ions. 



Mercuric iodide affords an excellent illustration of the prin- 

 ciple stated owing to the large variety of solvents for it. 



In hot ethylic alcohol it dissolves easily. Solution absolutely 

 colorless, gives a cloud when poured into water which settles 

 to a red powder. 



Methylic alcohol acts similarly. 



In solution of calcium chloride, especially if hot, dissolves 

 easily. Less easily in barium chloride. 



In solution of potassium and sodium chlorides dissolves 

 sparingly. All these solutions are colorless. 



In solutions of potassium bromide and of iodide it dissolves 

 abundantly. Strong solutions have a yellowish color but 

 become colorless by moderate dilution. These two salt solu- 

 tions dissolve mercuric iodide freely in the cold ; the other sol- 

 vents need heat. 



In cold solution of mercuric nitrate, it dissolves easily to a 

 colorless solution. In solution of mercuric chloride it is some- 

 what soluble ; the solution is colorless. 



In glycerine it dissolves pretty well with the aid of heat and 

 does not communicate a trace of color. 



Mercuric arsenite is bluish gray. It is slightly soluble in 

 solution of sodium arsenite. The solution is colorless. 



Mercuric arsenate is pale yellow. It dissolves in a solution 

 of mercuric nitrate and also in one of sodium pyrophosphate ; 

 both solutions are colorless. 



The black heavy metallic sulphides are very difficult sub- 

 stances to bring into solution, but it seems that when this can 

 be done the solution is colorless when the ions are colorless. 

 This can be shown to be the case with mercuric sulphide and 

 with antimony tri-sulphide. According to Weber,* when mer- 

 curic chloride is precipitated with an excess of ammonium 

 sulphide the precipitate dissolves in potash to a colorless solu- 

 tion. 



Silver oxid is slightly soluble in water. Being very deeply 

 colored, it would seem natural that its solution should show this 

 color. But the solution is absolutely colorless. This is because 

 the silver ion is colorless. Metallic oxids having colored ions 

 carry that color into their solutions, as is seen in the case of 

 cupric oxid in alkaline solutions and in soluble forms of ferric 

 oxid. 



Silver arsenite is lemon yellow ; it is abundantly soluble in 

 ammonia water and in mercuric nitrate. Both solutions are 

 colorless. 



*Cf. Gmelin-Kraut, iv, page 851. 



