58 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [bull. 176. 
Having regard to the presence of vanadium. — If vanadium is present 
the value found for iron will be in error by the amount of perman- 
ganate required to oxidize V 2 4 to V 2 5 . The amount of the cor- 
rection will differ according as titration of the iron is made after reduc- 
tion by hydrogen sulphide or by nascent hydrogen. If the former is 
used, as should always be the case, because of the ever present titanium, 
the vanadium is reduced by it to V 2 4 , which in its action on perman- 
ganate is equivalent to two mofecules of FeO, while the reduction goes 
further with hydrogen. After the first transitory pink blush through- 
out the liquid, the slower-acting vanadium may require the addition of a 
drop or two more of permanganate before a comparatively permanent 
coloration appears. 
When the amount of vanadium in the rock is known a correction 
can be applied on the assumption that practically all the vanadium is 
here collected, a point that needs further investigation. Various 
authors assert its precipitability with alumina and iron by ammonia 
and ammonium-acetate, though Carnot 1 states that repeated precipita- 
tion by ammonia, ammonium carbonate, or ammonium sulphydrate, 
separates it from iron. The writer's experience with ores very rich in 
vanadium shows that precipitation along with iron and aluminum is 
only partial. Ridsdale 2 has determined its precipitability with various 
metals and gives numerous figures which show an approximation to 
90 per cent thus thrown down under the conditions prevailing in analy- 
sis of iron slags, the remainder passing into the filtrates and appearing 
in small part with the lime and to a greater extent with the magnesium 
phosphate. For all practical purposes it is probably safe to assume 
that the small amounts of vanadium met with in rocks are wholly in 
the alumina precipitate. 
If the amount of vanadium in the rock is not known and great accuracy 
is necessary, caution requires the determination of the total iron to be 
made either in a separate portion or after reprecipitation from the 
above solution, as follows: Fuse with sodium carbonate, extract with 
water, bring the insoluble residue into sulphuric solution, reduce and 
titrate as above directed. But unless a certain precaution is here 
observed an error greater than that which it is designed to avoid will 
be committed. Contrary to general belief the aqueous extract from 
the sodium-carbonate fusion carries a small but appreciable fraction 
of a per cent of iron, as the writer has repeatedly found by actual test. 
This iron is thrown out with the alumina (and silica, if present) hj the 
usual methods of neutralizing the alkaline solution, and can be brought 
to light when the precipitate thus formed is treated with a fixed caustic 
alkali, or again fused with sodium carbonate and leached with water, 
'Comptes Rendus, Vol. CIV, p. 1803, 1887; Zeitschr, fur. anal. Chcm., Vol. XXXII, p. 223, 1893. 
2 Jour. Soc. Chem. Industry, Vol. VII, p. 73, 1888. 
