74 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
will almost always be found lower than the truth, probably for the 
reason that there are opportunities during the analysis for slight losses. 
It is best to estimate it in a separate 2-gram portion, which may also 
serve with advantage for the estimation of zirconium and total sulphur. 
Modes of attack and subsequent treat?nent. — If zirconium and sulphur 
are not to be looked for, the simplest procedure is to decompose the 
powder by sulphuric and hydrofluoric acids (seep. 69, under Titanium), 
and to complete the purification of the barium sulphate thus obtained 
in the manner described in the third paragraph below. 
If zirconium and sulphur are both to be likewise determined, decom- 
position is effected by fusing over the Bunsen flame and then over the 
blast with sulphur-free sodium carbonate and insufficient niter to 
injure the crucible, first fitting the latter snugly into a hole in asbestos 
board (Lunge) to prevent access of sulphur from the gas flame. In 
case sulphur is not to be regarded, the niter and asbestos board are 
omitted. After thorough disintegration of the melt in water, to which 
a drop or two of methyl or ethyl alcohol has been added for the pur- 
pose of reducing manganese, the solution is filtered and the residue 
washed with a very dilute solution of sodium carbonate free from bicar- 
bonate. This is to prevent turbid washings. A yellow color in the 
filtrate indicates chromium. 
For the further treatment of the filtrate see Sulphur, p. 106, and 
Chromium (colorimetric method), p. 80. 
The residue is dissolved in quite dilute warm sulphuric acid (stronger 
acid may be used if barium only is sought) and filtered through the 
original filter. This, with its contents, is ignited, evaporated with hydro- 
fluoric and sulphuric acid, and taken up with hot dilute sulphuric acid. 
The filtrate, added to the former one, now contains all the zirconium 
(see pp. 75-76 for its further treatment). The residue contains all the 
barium, besides some of the strontium, and perhaps a good deal of 
calcium. It is fused with sodium carbonate, leached with water, the 
residue dissolved off the filter by a few drops of hydrochloric acid, 
from which solution the barium is thrown out by a large excess of sul- 
phuric acid. A single solution of the barium sulphate in concentrated 
sulphuric acid and reprecipitation by water suffices to remove traces 
of calcium which might contaminate it if the rock was one rich in cal- 
cium, and even strontium is seldom retained by it in quantity sufficient 
to give concern. Should this be the case, however, which will occur 
when the SrO and BaO are together in the rock in, roughly speaking, 
0.2 and 0.4 per cent, respectively, the only satisfactory way is to 
convert the sulphates into chlorides and to apply to the mixture the 
ammonium-chromate method of separation (p. 63). 
Barium and strontium sulphates can be brought into a condition for 
testing spectroscopically by reducing for a very few moments the 
whole or part of the precipitate on a platinum wire in the luminous 
