56 SOME PRINCIPLES AND METHODS OF ROOK ANALYSIS, [bull. 175. 
The filtrates are strongly concentrated separatel}- ! in platinum, a 
drop or two of ammonia being added toward the end to the second 
one, and filtered successively through the same small filter into a iiask 
of 150 to 200 cm. 3 capacity, the ammoniacal filtrate serving as wash 
water for the first dish and containing enough ammoniacal salt to pre- 
vent precipitation of magnesium in the first filtrate when mixed with 
it. If manganese has been deposited upon the surface of the dish it is 
removed by hydrochloric and a drop or two of sulphurous acids, which 
mixture is then passed hot through the filter. A reprecipitation by 
ammonia is then made, and the precipitate collected again on the filter 
and added to the main one, the filtrate passing into the flask contain- 
ing the previous one. If much manganese is present, of course a second 
precipitation by ammonia of the small precipitate may be required c 
In these cases there is no difficulty in getting all the manganese into 
the filtrate. 
IGNITION OF THE PRECIPITATE. 
The combined precipitates of alumina, etc. , are ignited moist, in the 
paper, unless considerable iron is present, when the main one is dried, 
removed as far as possible from the paper, and the latter ignited sep- 
aratety to prevent partial reduction of a portion of the iron, which 
can not then be wholly reoxidized by heating or by treatment with 
nitric acid (see p. 38). 
Alumina in the quantities ordinarily found can not be fully dehy- 
drated by the full heat of the Bunsen burner. It must be blasted for 
five or ten minutes. If iron is present in large amount this last opera- 
tion must be conducted so as to insure free access of air to the crucible 
(p. 51). 
RECOVERY OF SILICA AND POSSIBLE BARIUM IN THE ALUMINA PRECIPITATE. 
The precipitate is dissolved by fusion with acid potassium sulphate, 
an operation which is accomplished without trouble in from two to 
four hours if the temperature is kept low and the acid salt has been 
properly made free from water and excess of acid. The melt is taken 
up with hot water and considerable dilute sulphuric acid, the residue 
collected, weighed, and corrected by hydrofluoric and sulphuric acids 
for silica, which, as said before, rarely amounts to 1 milligram in 
weight, and further examined for barium (see p. 53) by dissolving any 
1 If, instead of sodium acetate, ammonia alone has been used to precipitate alumina, etc., it has 
sometimes happened in the experience of others than the writer that on concentration of the first 
filtrate a pale straw-colored precipitate appeared, which remained on the filter with the traces of 
alumina, that may also separate, although it is slowly soluble in hot water. This is said to be some 
compound of platinum, and attention is called to it here for the guidance of others who may notice 
it and be unaware of its character. 
