64 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
The volumes of solutions used should be largely reduced and the 
operations otherwise shortened. 
The chlorides corresponding to 0.2774 gram BaO and 0.4864 gram 
SrO were dissolved in 300 cm. 3 of water with addition of 6 drops of 
acetic acid (1.065 sp. gr.). To the hot solution was added an excess 
(10 cm. 3 ) of ammonium chromate solution (1 '"cm. 8 ='0.1 gr. neutral 
chromate). After settling and cooling for an hour the precipitate was 
washed, mainly by decantation, with water holding ammonium chro- 
mate till the nitrate gave no precipitate with ammonia and ammonium 
carbonate (100 cm. 3 used). The washing was continued with warm 
water till silver nitrate gave but a very slight reddish coloration (110 
cm. 3 ). The precipitate was then washed into the precipitating dish, 
the filter rinsed with warm dilute nitric acid (1.2 sp. gr.), and more 
nitric acid (2 cm. 3 in all) added to the dish. The solution having been 
diluted to 200 cm. 3 and heated, 5 cm. 3 of ammonium acetate solution 
(1 cm. 3 = 0.31 gr. ammonium acetate) was very gradually added, and 
then ammonium chromate till the odor of acetic acid had wholly dis- 
appeared (10 cm. 3 ). After one hour the supernatant liquid was passed 
through the filter and the precipitate digested with hot water, which 
was then cooled; thereupon the precipitate itself was brought on the 
filter and washed with cold water till silver nitrate gave a scarcely 
perceptible reaction. The strontium was thrown down from the filtrate 
by ammonia and ammonium carbonate, after concentration in pres- 
ence of a little nitric acid, and weighed as carbonate; or the carbonate 
can be redissolved, precipitated by sulphuric acid and alcohol, and 
weighed as sulphate. The barium is weighed as chromace after igni- 
tion, the filter being burned separately. 
XL MAGNESIUM. 
PRECIPITATION. 
The first precipitation of magnesium is made without special precau- 
tions in the filtrate from the first calcium oxalate separation (p. 62) by 
sodium-ammonium-hydrogen phosphate (microcosmic salt) 1 in indefi- 
nite decided excess and without the great excess of ammonia usually 
prescribed. It is not necessary to first remove ammoniacal salts unless 
very little magnesium is present, and then only in order to hasten pre- 
cipitation. Neubauer 2 has shown that precipitation is complete even in 
presence of large quantities of salts of ammonium, including the oxalate. 
He has, however, also shown that the composition of the precipitate is 
largely affected by ammonium salts, and also by the way in which the 
iThe objection that has been made by one writer to the use of this salt instead of disodiuru-hydro- 
gen phosphate is, so far as our experience teaches, entirely groundless. 
2 Zeitschr. fur angew. Chemie, 1896, p. 435. 
