hillebrand.] PHOSPHORUS, CHROMIUM. 7 ( .) 
PROCEDURE WHEN MATERIAL IS SCANTY. 
The following procedure admits of determining in the same portion, 
besides phosphorus, barium, iron, vanadium, chromium, and titanium, 
the last two cither colorimetrically or gravimetrically, and is in large 
part extracted from a paper by Dr. T. M. Chatard. 1 
Silica is removed by hydrofluoric and sulphuric acids, excess of flu- 
orine expelled, the residue brought into solution as far as possible with 
sulphuric or hydrochloric acid and hot water, filtered, the residue 
ignited, fused with sodium carbonate, dissolved in hydrochloric acid, 
and the solution, after precipitation of barium, added to the main one, 
which is now precipitated by ammonia to get rid of the magnesium 
salts usually present and thus insure a cleaner subsequent fusion with 
sodium carbonate. 
The precipated A1 2 3 , P 2 5 , Cr 2 3 , Fe 2 3 , and Ti0 2 is dissolved in 
hot hydrochloric acid and filtered into a large platinum crucible, the 
filter burned and added, the solution evaporated to pastiness, a little 
water added to dissolve the salts, and dry sodium carbonate added in 
portions and stirred in thoroughly to prevent lumpiness in the fusion 
to follow, which is continued for half an hour. Addition of sodium 
nitrate is not necessary. 
The fused mass is boiled out with water and washed with very dilute 
sodium-carbonate solution. In the residue iron and titanium can be 
determined by the methods already described. In the filtrate chro- 
mium can be determined colorimetrically if present in sufficient 
amount to give a pronounced color (see p. 80). Afterwards, or imme- 
diately if the chromium is not to be thus estimated, enough ammonium 
nitrate is added to react with all the carbonate and the solution is 
digested on the bath till most of the ammonium carbonate is gone. 
Nearly, if not quite all alumina is thus thrown out, carrying with it all 
phosphorus. The precipitate is washed with dilute ammonium-nitrate 
solution till the yellow color wholly disappears, after which it is dis- 
solved in nitric acid and the phosphorus thrown out by molybdate 
solution. The filtrate, containing chromium and vanadium, can be 
treated as detailed in the next following sections. 
XVII. CHROMIUM. 
If vanadium is absent, or nearly so, as is apt to be the case in those 
highly magnesian rocks (peridotites) usually carrying a good deal of 
chromium, the following separation and gravimetric method for chro- 
mium gives good and concordant results, but in presence of vanadium, 
and it is best generally to assume its presence, the colorimetric method 
should always be adopted. 
i Am. Chem. Jour. Vol. XIII, p. 10G, 1891; Bull. U. S. Geol. Survey No. 78, i>. 87; Chemical News, 
Vol. LXIII, p. 267, 1891. 
