416 Prof. F. von Kobell on Dianie Acid. 
this treatment any tungstic or molybdic acids which might have 
caused the reaction described below was got rid of. 
In order to employ in my experiments as equal quantities as 
possible of the precipitates, which must be used when just 
thrown down, I made funnels of tinfoil, which I cut into the 
form of a filter one inch long in the side, and gave them the 
requisite shape in a small por celain funnel. One of these funnels 
was filled with the freshly filtered pasty precipitate by means of 
a spatula, and then laid in a porcelain dish; the tinfoil having 
been opened out, one cubic inch of concentrated hydrochloric 
acid, of the specific gravity of 1:14, was added and heated to 
boiling, that temperature being maintained for three minutes, 
and the foil kept continually well stirred about in the fluid. 
Under this treatment the appearances observed were as follows. 
1. The acid of the tantalite from Kimito, and of the niobite 
from Bodenmais, coloured the liquor bluish (smalt-blue); on 
adding half a cubic inch of water thereto, when poured into a 
glass the colour disappeared rapidly, the precipitate settled 
without being dissolved; on being filtered the liquor gave a 
colourless filtrate, and the precipitate, which at first was of a 
bluish tint, became speedily white on a further addition of water. 
2. The acids of a so-called tantalite from Tammela, the powder 
of which was blackish grey, those of euxenite, zeschynite, and 
samarskite, on being boiled with hydrochloric acid and tinfoil 
as above described, were dissolved to a dark blue cloudy fluid, 
which, when diluted with half a cubic inch of water or rather 
more, became perfectly clear with a deep sapphire-blue colour, and 
gave a transparent deep-blue filtrate. On being further diluted 
by the addition of a twofold or threefold quantity of water, the 
colour becomes indigo-blue and bluish green; and in open 
vessels, after some time, olive-green, maintaining that tint for 
several hours, but becoming paler. The fluid preserves its per- 
fect transparency all the while, and in a closed vessel the colour 
remains unchanged for weeks. 
Both with the assays under (1), and also with those under 
(2), I kept up the boiling for a longer time, indeed till the 
liquors were tolerably concentrated ; I then added half the 
volume of water and poured the whole into a glass. The 
appearances observed were the same as before; the acids of (1) 
remained undissolved and gave a colourless filtrate, while those 
of (2) were dissolved and gave a transparent blue solution, the 
colour of the filtrate being also blue. When treating euxenite 
on one occasion, and conceutrating the liquor by boiling, obtained 
an olive-green fluid, which was, however, transparent; on the 
addition of concentrated hydrochloric acid, and boiling a second 
time with tinfoil, the blue colour was restored. If, on obtaining 
