144 
IOWA ACADEMY OF SCIENCE 
KCIO3 + 6HC1 = KCl + 6C1 + 3H2O. 
K3ASO4 + 3HC1 = H3ASO4 + 3KC1. 
2H3ASO4 + 5H2S = AS2S5 + 8H2O. 
After the first filtration of the arsenic, the iron is next determined, followed 
by the estimation of nickel and cobalt as follows: The filtrate from the iron 
is evaporated to a smaller volume, and both nickel and cobalt are precipitated 
as hydrates with caustic potash. The hydrates are filtered off, removed with a 
feather to an evoporating dish, and hydrocyanic acid is added until a reddish 
tint, not very pronounced, is assumed; then a solution of caustic potash, drop 
by drop, until all is dissolved save a small flocculent precipitate of cobalt para- 
cyanide. This is filtered through the same paper from which the precipitates 
were removed. 
The filtrate is concentrated to a small volume, and mercuric oxide, sus- 
pended in water is added until the liquid remains a red color. This is Liebig’s 
method of precipitating the nickel. It is left about an hour on the water bath, 
when the nickel is removed by filtration. 
The Coltalt. The filtrate from which the nickel was removed is evaporated 
to dryness in a platinum dish. The cobalt paracyanide is now united to this 
main portion. About 30 c. c. dilute sulphuric acid are added, and after half an 
hour the same quantity of strong acid. It is evaporated to as small a bulk as 
possible on the water bath, and cautiously heated with the free flame to 
remove all sulphuric acid. The residue is treated with a little water and the 
mercury salt that it usually contains is removed by filtering. The filtrate is 
once more evaporated to dryness, and again filtered to remove the last traces 
of mercury. 
The filtrate on the water bath is precipitated hot with a solution of caustic 
potash. The well washed precipitate is finally reduced to metallic cobalt with 
a stream of hydrogen. 
The reactions: 
Co(N03)2 4- 2 KOH = Co(OH)2 4- 2KNO3 
Co(OH)2 4- 2 HCN = Co(CN)2 4- 2H2O. 
KOH and HCN are added until the double salt, potassium Cobalto Cyanide, 
Co(CN)2, 4KCN is formed. Expressing this double salt in another way we have 
K4 Co"(CN)e. 
2K4 C0(CN)6 4- 0 4- H2O = 2K3 Co"'(CN )6 + 2KOH. 
There is a change of valence from two to three. 
Adding dilute sulphuric acid there results: 
K3Co(CN)e 4- 3H2SO4 = 3HKS04 4 - H3Co(CN)6. 
The concentrated sulphuric acid reacts as follows: 
2H3Co(CN)e 4- I9H2SO4 = 2C0SO4 4- 12CO 4- 12N 4- I7SO2 4- 22H2O. 
Heating to dryness changes the HKSO4' — 2HKSO4 = K2S2O7 4- H2O. 
C0SO4 4 - 2KOH = Co(OH)2 4- K2SO4 
Co (OH) 2 4- 2H = Co 4- 2H2O. 
