hillebrand.] ALUMINUM, TOTAL IRON. 59 
when it remains wholly or in part undissolved. Hence it is necessary, 
to collect this iron and add it to the main portion before tit rut ion. 
DETERMINATION OF TIIE TRUE VALUE FOR FERRIC [RON. 
Having in one way or another found the total iron in the rock, it 
remains to deduct an amount equivalent to the ferrous oxide the rock 
contains, and a further amount corresponding to the sulphides oil en 
present, in order to get what may pass for the true value for ferric 
iron. That this is often only an approximation appears from the diffi- 
culties due to the presence of vanadium and the generally indetermin- 
able effect of sulphides on the ferrous oxide determination. (See pp. 
94-96.) 
METHODS AIMING AT THE MORE OR LESS DIRECT ESTIMATION OF 
ALUMINUM. 
AFTER FIRST REMOVING IRON AS SULPIIIDE. 
Should it be desirable for any reason to effect an actual separation 
of aluminum, this may best be done, up to a certain point, after the 
bisulphate fusion (p. 56), by removal of the iron 1 by ammonium sul- 
phide in ammonium tartrate solution, evaporation of the filtrate, igni- 
tion of the residue with sodium carbonate and nitrate, and extraction 
with water, whereby titanium and zirconium are left on the filter as 
sodium salts while chromium and vanadium are carried into the filtrate 
as chromate and vanadate along with aluminum and phosphorus. The 
further separation of the two last from the chromium and vanadium is 
outlined under Phosphorus, p. 79. This is as far as the separation can 
well be carried, and the Al a 3 must still be found by subtracting the 
P 2 5 from the combined weights of the A1 2 3 and P 2 5 . The possi- 
bility of loss of some P 2 5 by volatilization 2 during the bisulphate 
fusion must be borne in mind here, for if it takes place the final weight 
of A1 2 3 + P 2 5 will not contain all the P 2 5 . 
Some writers recommend dissolving the ignited alumina, iron oxide, 
etc., in rrydrochloric acid, but when the precipitate has been heated 
over the blast, as it should be, this is very ineffective. 
BY EXTRACTION WITH A FIXED CAUSTIC ALKALI. 
A favorite practice in some countries of Europe is to fuse the ignited 
precipitate containing A1 2 3 , Fe 2 3 , Ti0 2 , P 8 B , etc. — or that of the 
A1 2 G 3 , Ti0 2 , P 2 5 , etc., after separation of iron by ammonium sulphide 
in tartrate solution — with sodium hydroxide in a silver crucible, or to 
x This being first reduced to the Ferrous condition by hydrogen sulphide in acid solution in order t<» 
obviate the possibility of precipitating some titanium, which otherwise is likety to happen. (Cathrein, 
Zeitschr.ftir Kryst, Vol. VI, p. 246, 1882, and Vol. VII, p. 250, i 
2 II.Rose speaks of such loss when volatilizing sulphuric acid in presenc phosphoric acid. 
(Handb. f. quant. Anal., Finkener edition, Vol. II, p. 575, and elsewhere.) 
