HiLLEBRAM.l ALUMINUM, TOTAL IRON. 55 
in any case the probable error can hardly be as high as that involved 
in the direct weighing of the alumina itself, considering the difficulty 
of effecting a satisfactory separation of it from all the oilier admix- 
tures, an operation which would, moreover, immoderately extend the 
time required for each analysis. 
PRECIPITATION <>F ALUMINUM, [RON, ETC. 
Precipitation by ammonia, — Two precipitations by ammonia at boil- 
ing heat are usually quite sufficient to separate iron, aluminum, phos- 
phorus, vanadium, chromium, titanium, and zirconium, it* all these arc 
present, from nickel, manganese, the alkaline-earth metals, and mag- 
nesium, provided ammoniacal salts are present in sufficient quantity. 
This last point is of special importance as regards magnesium, and 
failure to observe it is doubtless the reason why many old analyses, 
and sometimes modern ones, show utterly improbable percentages of 
alumina, especially as chemists were formerly often satisfied with a 
single precipitation. The necessary ammonium chloride is better 
obtained by the use of purified ammonia water and hydrochloric acid 
than by the addition of the solid salt, which is seldom pure. 
Precipitation by the basic acetate method. — But it will occasionally 
happen that the separation from even very small amounts of manga- 
nese is altogether incomplete, and the uncertainty of insuring this 
separation has led the writer of late to employ the basic acetate method 
for the first precipitation in all cases where manganese is present — and 
the exceptions are few — even though the precipitation of alumina is 
sometimes less complete than by ammonia, and in spite of other 
admitted defects, as, for instance, a tendency of the precipitate to run 
through the filter on washing. 1 Not more than 2, or at most 3, grams 
of sodium acetate need be used. After slight washing and sucking 
dry at the pump, the precipitate is redissolved in a large excess of 
hydrochloric acid and reprecipitated by ammonia in slight excess. 
The complete boiling off of this excess is unnecessary, as pointed out 
by Genth and Penfield, since it is apparently the washing with pure 
water and not the free ammonia which carries small amounts of alumina 
into the filtrate. Penfield and Harper 2 recommend washing with a 
dilute solution of ammonium nitrate (20 cm. 3 nitric acid, neutralized 
by ammonia, to the liter), and also the solution of the first precipitate 
in nitric instead of hydrochloric acid, in order to shorten the washing, 
there being no chloride to remove. 
J The fact must not be overlooked that certain of the rare earths may pass completely into the 
filtrate if the basic acetate method is followed. If then, later, on rendering the combined fill 
ammoniacal, an unexpectedly large precipitate appears, this should be carefully examined as to its 
nature. In an analysis of piedmontite from Maryland over 2 per cent of tare earths, including cerium 
and others not identified, were quantitatively separated in this way from iron, alumina, etc. 
2 Am. Jour. Sci., 3d series, Vol. XXXII, p. 112, 1886. 
