50 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
are added and the oxygen blast is applied till, in ten or fifteen min- 
utes, the fusion is as transparant as glass. 1 
Further treatment after fusion. — From this point the further treat- 
ment is the same in both cases, and as modified by Jannasch and 
Weber (loc. cit.) is as follows: 
The hot crucible is cooled in cold water and the contents are turned 
into a very large porcelain or platinum dish, to which, after covering 
with a glass, a saturated solution of hydrochloric acid gas in methyl 
alcohol is added. 2 The cover being then removed, the liquid is heated 
to boiling over asbestos board by an inch-high flame, stirring con- 
stantly, or it is left without attention over a lower flame or on a water 
bath heated short of boiling. The crucible is cleansed in a similar 
manner, and its contents are added to the dish. In ten to fifteen min- 
utes, with occasional addition of the meth} r l chloride, solution is 
complete and the liquid is then boiled down to a small volume and 
evaporated to dryness on the bath. The residue is then digested on 
a bath at 80° to 85° C. three or four times in succession, with the ether 
solution, in order to remove the last traces of boron as boric ether. 
Care should be taken to wash down from the sides of the dish, with 
methyl-chloride solution, the boric acid formed and deposited thereon 
during the evaporation. 
Possible objections to the boric-oxide method. — Very much is claimed 
by Jannasch for this method, but with all its undoubted merit there 
are two points which may militate against it in time. The boric ether, 
driven off in such enormous quantities, at once decomposes in contact 
with moisture, and boric acid settles over all objects with which it 
comes in contact. The hood must become thickly coated. Hence a 
special hood for these evaporations alone seems to be called for, other- 
wise boric acid may at any time fall into other dishes and cause untold 
trouble. The second objection attaches to the use of the oxygen flame 
when alkalies are to be estimated in the fusion, and the ability to so 
determine them is one of Jannasch's chief claims in favor of the 
method, for it can not be doubted that at the high temperature of this 
flame alkalies are volatilized in part. Borax can be slowly but wholly 
volatilized over the ordinary blast, hence there is great reason to fear 
sufficient loss at this much higher temperature to give rise to serious 
error at times. 
THE SODIUM-CARBONATE METHOD. 
Purity of the sodium carbonate used as a flux. — Notwithstanding the 
most earnest efforts for years, it has been impossible to procure, either 
1 An interesting and important observation reported by Jannasch and Weber is that when the 
oxygen blast has been used for silicates carrying fluorine or mixed with fluorides, the fluorine seems 
to be wholly expelled as boric fluoride, without loss of silica. If this should prove to be generally 
true, an easy way is at last afforded for estimating silica in such cases, where even its detection, 
when present in small amount, has heretofore been difficult. 
2 Made by passing dry HC1 into cooled CH 4 for from one to two hours. 
