ZINC. 
§ 894-] 
701 
mercurous compounds. For mercuric, the method of Personne 1 is the 
best. The conversion of the various forms of mercury into corrosive 
sublimate may be effected by evaporation with aqua regia, care being 
taken that the bath shall not be at a boiling temperature, or there will 
be a slight loss. 
Personne prefers to heat with caustic soda or potash, and then pass 
chlorine gas into the mixture ; the excess of chlorine is expelled by 
boiling, mercuric chloride in presence of an alkaline chloride not being 
volatilised at 100°. The standard solutions required for this process 
are :— 
(1) 33-2 grms. of potassic iodide in 1 litre of water, 1 c.c. =0-01 grm. 
Hg, or 0*01355 grm. HgCl 2 . 
(2) A solution of mercuric chloride containing 13-55 grms. to the 
litre, 1 c.c. =0-1 grm. Hg. 
The process is founded on the fact that, if a solution of mercuric 
chloride be added to one of potassic iodide, in the proportion of one of the 
former to four of the latter, mercuric iodide is formed, and immediately 
dissolved, until the balance is overstepped, when the red colour is 
developed ; the final reaction is very sharp, and with solutions properly 
made is very accurate. The mercuric solution must always be added to 
the alkaline iodide ; a reversal of the process does not answer. It there¬ 
fore follows that the solution to be tested must be made up to a definite 
bulk, and added to a known quantity of the potassic iodide until the 
red colour appears. 
Mercurous Salts may be titrated with great accuracy by a decinormal 
solution of sodic chloride. This is added to the cold solution in very 
slight excess, the calomel filtered off, the filtrate neutralised by pure 
carbonate of soda, and the amount of sodic chloride still unused found 
by titration with nitrate of silver, the end reaction being indicated by 
chromate of potash. Several other volumetric processes are fully 
described in works treating upon this branch of analysis. 
III.—PRECIPITATED BY HYDRIC SULPHIDE FROM 
A NEUTRAL SOLUTION. 
Zinc—Nickel—Cobalt. 
1 . ZINC. 
§ 894. Zinc —at. wt., 65 ; specific gravity, 6-8 to 7-1 ; fusing-point, 
412° C. (773° F.)—is a hard, bluish-white, brittle metal, with a crystalline 
fracture. Between 100° and 150° it becomes ductile, and may be easily 
wrought ; but at a little higher temperature it again becomes brittle, and 
1 Compt. Rend., lvi. 68 ; Sutton’s Vol. Anal., p. 177. 
