48 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
Another of their advantages is that with some of them it is possible 
to estimate in one portion the alkalies, in addition to those constituents 
usually determined in the silica portion . Where the material is limited, 
as it so often is in mineral analysis, this is a most important advantage, 
sufficient to outweigh all possible objections; but in rock analysis, where 
the supply of material is usually ample, it is rarely worth consider- 
ing. A still further point in their favor is that it is probably more 
easy to obtain them entirely free from fixed impurities than an alkali 
carbonate. 
There are, however, objections to their use. With some of them an 
extraordinary amount of time must be devoted to grinding the mineral 
to an impalpable powder, and the flux itself may need considerable 
hand pulverization. Once introduced, they must be removed before the 
analysis can be proceeded with, and this removal takes much time and 
is always a possible source of error. 
In mineral analysis these objections are entitled to far less weight 
than in rock analysis, since the object sought— usually the deduction 
of a formula — warrants the expenditure of much time and painstaking 
care. Finally, it has been found that one or more of these fluxes are 
not available for altogether general use, since certain minerals do not 
fully succumb to their attack under simple conditions, as andalusite 
with boric oxide and others with lead oxide (Jannasch). Therefore, 
however well adapted one or the other of these methods ma} 1 - be for the 
analysis of homogeneous minerals, it is veiy improbable that the vivid 
anticipations of Professor Jannasch, to the effect that the boric-oxide 
method will soon supersede the alkali-carbonate-fusion method in rock 
as well as in mineral analysis, will be speedily realized. Neverthe- 
less, the boric-oxide-fusion method, owing to its evident merit, will be 
described in detail after brief reference to a means of bringing refrac- 
tory silicates into solution without employing any solid reagent. 
DECOMPOSITION OF REFRACTORY SILICATES BY HYDROCHLORIC ACID UNDER PRESSURE. 
Jannasch l pours upon the finely ground rock powder contained in a 
platinum tube of about 26 cm. 3 capacity a somewhat diluted hydro- 
chloric acid (4 acid to 1 water), places over the open end a cap which 
does not hermetically close the tube, inserts the latter in a larger one 
of potash glass likewise partially filled with the diluted acid, seals the 
glass tube, and places it in turn in an inclined position in a steel 
Mannesmann tube containing ether or benzine to equalize the pressure, 
and heats to any desired temperature up to 400° C. 
The chief drawback seems to be a somewhat incomplete decomposi- 
tion, doubtless due to the necessarily inclined position of the tube, 
which causes the powder to collect at the lower end, and thus renders 
iBer. (leutseh. chem. Gesell., Vol. XXIV, p. 273, 1891, and Zeitschr. fiir unorg. Chem., Vol. VI, p. 72, 
