116 ANNUAL REPORYS 
bulky, decant three times. Then transfer to the filter, wash, ignite and 
weigh as alumina and ferric oxide. 
If it is desired to determine the ferric oxide in the material the 
quickest way of determining it is carr-ed out as follows: Take two grams 
fuse with 6 grams of sodium carbonate and separate the silica as 
given above. After removal of the silica transfer the filtrate, acid 
with hydrochloric acid, to a 500 cc. flask and divide it into two 
portions, one of them being retained for the determination of the alumina 
and ferric oxide together, and of the calcium and magnesia; in the other 
half the iron is determined volumetrically by the bichromate method. 
This is much more rapid than the solution of the ignited oxides of 
alumina and iron in potassium disulphate or sulphuric acid and titration 
with potassium permanganate. Of course for quick work, one gram may 
be used and this divided into two portions. 
Heat the filtrate from the alumina and iron to boiling and add excess 
of a hot saturated solution of ammonium oxalate. Stir and allow 
to stand for five minutes. Tilter off the supernatant clear liquid, and 
add boiling water to the precipitate remaining in the first beaker together 
with sufficient hydrochloric acid to redissolve the calcium oxalate. aise 
again to boiling, add a little ammonium oxalate and make ammoniacal. 
Now allow the precipitated calcium oxalate to stand for one hour, 
filter and wash it, the filtrate being allowed to run into a fresh beaker. 
If in the first filtrate any precipitate is formed meanwhile, it must be 
filtered through the paper before the main precipitate is transferred. 
The chief consideration in the calcium determination 1s that the work 
must be carried on as hot as possible, the solution and wash water being 
boiling hot. For very accurate work, the solution should stand for 12 
hours in order to bring about complete precipitation of the lime. In 
rapid technical work, not more than ten minutes is allowed for standing, 
usually five. The difference between the five minute and 12 hours stand- 
ing may be % per cent. If the work is done with boiling solutions the 
deficit is considerably less than this. In rapid work with rock low 
in magnesia, the re-solution and precipitation is not necessary, but cannot 
be avoided in the case of magnesian stone. 
Tenite the precipitate of calcium oxalate over the blast lamp, cool, and 
add enough nitric acid to dissolve the oxide. Now add five or six drops 
of sulphuric acid and take the mass to dryness by heating gently with 
a Bunsen flame till the white fumes of sulphuric acid have ceased coming 
off. If no sulphuric acid fumes are seen, add more sulphuric acid 
and reheat. Then bring the residue to a dark red heat over the Bunsen 
flame and weigh it as calcium sulphate. | 
With a good blast lamp it is possible toignite the calcium oxalate to 
the oxide and to weigh as such. In technical control work, the calcium is 
determined with sufficient accuracy volumetrically as described under the 
head of the examination of calcareous Portland cement material. 
