200 F. W. Clarke— Electrolytic estimation of Mercury. 
very unstable that we could obtain but a very small quantity 
f them, and in a somewhat impure condition. They yielded 
48°31 per cent of gold, whereas the salt KAu(CSeN),, analo- 
gous to the potassio-aurous sulphocyanate of Cleve, should con- 
tain but 43°94. As the new salt was prepared by a method 
precisely similar to that which gave Cleve his sulphocyanate, 
there can be little doubt that we had to deal with the corres- 
ponding seleniocyanate, mixed with free gold. If we had been 
able to command larger quantities of material, we might have 
been able to prepare the compound in a state more nearly 
approaching purity. 
No seleniocyanate resembling Roesler’s potassium chromo- 
sulphocyanate, K,Cr(CSN),,, 8H,O,* could be obtained. 
When aqueous solutions of chrome alum and potassium selenio- 
cyanate are mixed, selenium is precipitated, and no trace of any 
double salt seems to be formed 
VIIL. On the Electrolytic estimation of Mercury. 
In 1865, Wolcott Gibbs published his well known method 
for the electrolytic estimation of copper.t More recently, 
Merrick has shown that a modification of the same process is 
eety precipitated by electrolysis from an ammoniacal solution, 
ut i 
* Journ. fir Prakt. Chem., cii, 316. — + This Journ. xxxix, 64. 
¢ American Chemist, October, 1871; Chem. News, xxiv, 100, 172. 
