hillebkand.] SILICA, SEPARATION FROM ALUMINA, ETC. 4\) 
decomposition less complete than if the material were spread evenly 
throughout the length of the tube. Further, the acid strongly attacks 
the platinum unless the air in both the platinum and the glass tubes is 
replaced by carbon dioxide. Even when this is done, several milli- 
grams of platinum are found in the silicate solution. 
Nevertheless, to those possessing the necessary platinum and steel 
tubes the method can render efficient service in special cases when 
economy of material is imperative. 
THE BORIC OXIDE METHOD OF JANNASCH AND 1IEIDENREICII. 1 
Preparation of the boric oxide. — This demands, if the alkalies are to 
be estimated in the same portion as silica, etc., an absolutely alkali- 
free boric acid, which can be prepared by two or three reerystalli- 
zations of a good commercial article. The purified crystals are 
dehydrated and fused in a large platinum crucible. This is then sud- 
denly cooled to cause the anhydride to crack into pieces of a size con- 
venient for powdering, which are to be kept in a tight glass and 
powdered as needed, since the anhydrous oxide is hygroscopic. 
Treatment of easily decomposable silicates. — To this flux Jannasch 
and Heidenreich find that nearly all silicates readily succumb over the 
ordinary blast lamp. The fusion is made in a large crucible holding 
40-65 cm. 3 , and the proportion of flux to be used is gauged according 
to the nature of the silicate, ranging from 3 to 8 and more parts to 1 
of mineral. This last must be finely powdered, especially the most 
resistant, the authors recommending the expenditure of one-half to 
one hour's time for the grinding of one-half to 1 gram of powder. 
A low burner heat is applied for five to ten minutes till water is 
expelled, which is then gradually increased till the gas is fully turned 
on. Bubbling and rising in the crucible is prevented as far as possible 
by using a short platinum rod which does not reach above the edge of 
the crucible. When the mass has been in quiet fusion for a time in 
the covered crucible the blast flame is applied. The average duration 
of the entire operation is twenty to thirty minutes, but depends much 
on the character of the mineral. 
Treatment of refractory silicates. — For those minerals which, like 
andalusite, cyanite, and topaz, are not fully decomposable by the heal 
of the ordinary blast flame, Jannasch and Weber 2 use a flame fed by 
oxygen instead of air. The blast lamp, of 2? mm. opening, is sup- 
plied with gas from at least five or six ordinary gas cocks, and the 
flame is made broad and free from luminosity. The mineral having 
been first heated as above described, but with a much larger propor- 
tion of flux — as hio-h as 30 to 1 — a few grams additional of boric oxide 
i Zeitschr.furanorgjChem.,Vol.XII,p.208,1896. 
2 Ber. deutsch. chem. Gesell., XXXII, p. 1670, 1899. 
Bull. 176 4 
