Prof. F. von Kobell on Dianie Acid. 417 
a green fluid of this nature, it is diluted with three times its 
volume of water and then slowly evaporated tillit becomes tur- 
bid, on the addition of a suitable quantity of concentrated hydro- 
chlorie acid and boiling for a few minutes with tinfoil, the blue 
colour of the solution always appears on adding a little water. 
It seems superfluous to say that a transparent blue fluid 
also gives a filtrate of the same colour; and yet the case occurs 
of such a fluid being coloured only from some substance being 
held suspended therein in a state of extreme subdivision, the 
filtrate being colourless. Such, for instance, is the behaviour of 
tungstic acid when it is precipitated from tungstate of potash 
with hydrochloric acid, and the precipitate boiled with con- 
eentrated hydrochloric acid and tinfoil. I obtained thus a dark- 
blue fluid, which, when considerably diluted, was quite trans- 
parent and of a bright sapphire-blue; but both the dark-blue 
and the light-blue diluted fluid gave a colourless filtrate; and 
when left to themselves, both these fluids also became colourless 
when the blue oxide of tungsten suspended therein, and which 
in that condition retains its blue colour, had settled to the 
bottom. 
The tin contained in the blue solution of the acid in question 
is easily got rid of by a stream of sulphuretted hydrogen, and 
the acid is obtained again from the filtrate. by precipitation with 
ammonia. ‘The precipitate, on being boiled with hydrochloric 
acid and tinfoil, again produces the blue fluid. On evaporating 
slowly the liquor filtered from the sulphide of tin (which from 
its diluted state is colourless), it becomes turbid when consider- 
ably concentrated. On adding a little water the cloudiness dis- 
appears, and on the further addition of concentrated hydrochloric 
acid a white precipitate is produced. If the hydrochloric acid 
has been added in suitable quantity, and if the fluid is boiled with 
a slip of tinfoil placed in it, the appearance spoken of above is 
produced. The fluid becomes of a deep blue, and when poured 
into a glass appears turbid; but on the addition of half its 
volume of water it becomes transparent, and presents itself in the 
glass like a clear sapphire. The original precipitate from the 
potash solution may be freed from any manganese it may contain 
by boiling it with a certain-quantity of hydrochloric acid; this 
precipitate can further be boiled with tolerably strong sulphuric 
acid without being deprived of the property of being soluble in 
hydrochloric acid in the presence of tinfoil. The acid thus puri- 
fied is white; on being heated, it assumes a very pale yellow 
colour, which it loses again on cooling, taking somewhat the 
appearance of porcelain. 
Before the blowpipe it is dissolved in borax and salt of phos- 
phorus to a colourless glass, both in the oxidating and the redu- 
Phil, Mag. 8. 4. Vol. 21. No. 142, June 1861, 25 
