422 Prof. F. von Kobell on Dianice Acid. 
sought to impart to the non-colouring tantalic and hyponiobic 
acids the quality of becoming coloured by an addition of tungstic 
acid, and then endeavoured to ascertain how far an acid. thus 
mixed was to be purified by ammonia, the process which I fol- 
lowed in my original experiments. I prepared tungstate of pot- 
ash of a determined strength, and mixed it with a lye of tantalic 
acid in such proportions that 84 parts of tantalic acid were united 
to 16 parts of tungstic acid, corresponding, as it were, to a pot- 
ash solution of a tantalite that consisted of tantalic and tungstic 
acids only. The mixture was divided into two portions. (by 
means of a graduated glass), and precipitated with hydrochloric 
acid. The precipitate of one portion was decanted and filtered, 
and a tinfoil filter, one inch long in the side, being filled there- 
with, it was boiled for three minutes in | cubic inch of hydro- 
chloric acid as described above; 14 cubic inch of water was 
added, and it was filtered. ‘The filtrate was greenish yellow; 
on adding 1 cubic inch more water the fluid was yellowish, the 
precipitate was not dissolved, and after the lapse of twenty- 
four hours the fluid which was poured off deposited a dark blue 
precipitate. The same experiment, performed in the like manner 
with a similar quantity of the hyponiobic acid, gave an olive-green 
filtrate, which did not materially change im twenty-four hours. 
When boiled again it became of a blue colour, which was also 
the hue of the filtrate. The hyponiobic acid was a little dissolved 
in this experiment, as the tantalic acid was in the corresponding 
one. When, however, I agitated the precipitates of the mixed 
acids with ammonia (the approximate quantity required to dis- 
solve the amount of tungstic acid contaied therein having been 
ascertained by experiment), and then allowed them to subside, 
decanted and filtered them, the precipitates thus treated, 
on being boiled for three minutes, as above described, with hy- 
drochloric acid and tinfoil, and diluted with half a cubic inch of 
water, behaved almost entirely like the acids prepared directly 
from the minerals themselves; the fluid of the tantalic acid 
passed through the filter colourless, that of the niobic acid had 
a slight greenish tint. These experiments prove that tantalic 
and hyponiobic acids, even when containing a great amount of 
tungstic acid, may be at least so far purified by ammonia as not 
to produce the deep blue colour given by dianic acid; and fur- 
ther, that the presence of tungstic acid in those acids, under the 
conditions spoken of, does not increase their solubility in hy- 
drochloric acid. The latter circumstance, although to be antici- 
pated, was of more importance to me than the absence of the 
blue colour; for similar experiments to these had already fully 
convinced me that the removal of tungstic acid by means of am- 
monia is not a perfect one. To remove, however, the last doubts 
