53 
results were confirmed by isolating the impurities and de- 
termining the calcium by precipitation as oxalate. The 
precipitates effervesced considerably on treatment with the 
acid. 
The above experiments suffice to indicate the magnitude 
of the obvious error which attends the common practice of 
separating iron and similar oxides from the alkaline earths 
by precipitation with excess of alkali. 
Since iron is very frequently separated from other metals 
in the form of the basic acetate, the purity of this com- 
pound, i.e. of the oxide which results from the washing and 
ignition of the same, was made the subject of the following 
determinations : 
yj Wt. Fe. 
v taken. 
Salt 
added. 
Wt. Fe. 
found. 
Error. 
Notes. 
w. -1995 
#. *2106 
NaCl 
NaCl 
•2007 
•2122 
•0012 ) 
•0016 j 
In all cases solution Fe 2 Cl 6 nearly 
> neutralised with (NH 4 ) 2 C0 3 and 
pptd. by NaC 2 H 3 0 2 in excess. 
i-j 
GO 
O 
CaCl 2 
•1825 
•0025 
Only a trace of Ca could be detected 
in the isolated impurity. 
0 . -1987 
CaCl 2 
•2000 
•0013 
Here as before it is seen that alkaline salt is retained by 
the iron oxide, but the separation of the latter from the 
alkaline earths is practically complete. 
The general conclusions to be drawn from the above 
results are : 
(1) . That ferric oxide, when precipitated in presence of 
salts of the fixed alkalis, removes a certain quantity of the 
latter from solutions, this quantity being within certain 
limits independent of the amount of alkaline salt present in 
solution, but varying with the temperature of the solution 
at the time of precipitation, being much greater in the case 
of cold than of hot solutions. (I, IV.) 
(2) . That the error due to the retention of alkaline salt 
may, by persistent washing with boiling water, be reduced 
to a minimum but not completely eliminated. (HI.) 
(3 y . That the error is very much greater when the oxide 
is precipitated by excess of alkali in presence of salts of the 
