Prof. F. von Kobell on Dianie Acid. 42] 
locality analysed by H. Rose, Weber, Jacobson, Brooke, Wornum, 
and Nordenskiold, had a specific gravity of from 7°38 to 7:5 and 
more. The tantalite from Kimito, moreover, from which I pro- 
cured the tantalic acid employed for my investigation, has a spe- 
cific gravity of 7:06. The colour of the streak of dianite is, as 
before remarked, black-grey, while that of the Tammela tanta- 
lites analysed by Jacobson is stated to be dark brownish red, as 
is also the case with the Kimito tantalite. 
In appearance dianite very closely resembles Finland tanta- 
lites. The assay analysed was taken from a large tabular broken 
crystal about 2 inches in size, on which, however, only two 
planes occur. Their angle of inclination, as measured by the 
hand-goniometer, amounts to about 151°; whether those planes 
are T and R of Naumann’s tantalite, or T and G, or other ones, 
cannot of course be determined. Lefore the blowpipe, dianite 
affords no marked difference when compared with the Kimito 
tantalite. 
The samarskite which I examined is from the IImen Moun- 
tains; I employed quite fresh, pure fragments, with a conchoidal 
fracture and strong, somewhat metallic, vitreous lustre. The 
euxenite is from Alva near Arendal (procured from Dr. Krantz) ; 
the eschynite, from the IImen Mountains, was from the Leuch- 
tenberg collection. 
While preparing the above, I forwarded a portion of the 
dianic acid in question to Professor Heinrich Rose, and communi- 
cated to him the leading points of the paper, requesting his 
opinion on the matter. Professor Rose was so good as to pre- 
pare the chloride of this acid, and wrote to me that, in doing so, 
he had met with a trace of tungstic acid, adding that the re- 
action described by me might be brought about from that cireum- 
stance; and he advised me, as a first step, to purify the acid by 
the method suggested by him, namely, by fusing it with car- 
bonate of soda and sulphur. The case might be similar to the 
one which had misled Hermann. 
Now I had, it is true, established, by the very ready solubility 
of dianic acid in hydrochloric acid when compared with true 
tantalic and hyponiobic acids under similar conditions, a 
characteristic distinction for the first of these three acids; 
but it was none the less essential to prove that the property 
of becoming blue with hydrochloric acid and tin belonged 
to the acid in question, and is not attributable to tungstic acid. 
After the treatment with ammonia, to which reference has been 
made, but little tungstic acid could, it is true, contaminate the 
dianic acid; nevertheless the turning blue might be ascribed to 
that. A plan to clear this pomt up was soon formed. [I first 
