Prof. F. von Kobell on Dianic Acid. 415 
taken at the same temperature ¢. According to Wolf and Brunner 
(Ann. de Chim. vol. xlix.), p= A—Odt is the empirical equation for the 
capillary height in terms of the temperature. According to the law 
, ‘ k \p) 
of expansion, m= ) . Hence 
Pein / (GE) 
is the equation which, at present partly empirical, it is so desirable 
to convert into one wholly expressive of a general natural law of 
quantitative relation between L and V. 
Edinburgh, May 6, 1861. 
LXII. On a peculiar Acid (Dianic Acid) met with in the Group 
of Tantalum and Niobium compounds. By Professor F. von 
KoBELu*. 
— G engaged in preparing a new edition of my ‘ Minera-- 
logical Tables,’ I was anxious, among other matters, to 
arrive at as distinct chemical characters as possible for the tan- 
talates and niobates with which we are familiar ; and after various 
experiments, [ came to the conviction that in several of these 
compounds there exists an acid different from the true tantalic 
acid which occurs in the tantalite from Kimito, and also from 
the niobic acid met with in the niobite from Bodenmais. 
As from the previous labours of MM. Rose, Hermann, 
Wohler, and others we are aware that in testing for these acids 
the one is very liable to be mistaken for the other, inasmuch as 
the tests give more or less various indications according to the 
manner of treating the substances and the quality of the reagents 
themselves, I have endeavoured in the first place to avert any 
possible error arising from those causes by conducting the whole 
of the assays in precisely the same manner, which I now proceed 
to describe in detail. 
1:5 grm. of each assay was fused in a silver crucible with 12 
grms. of hydrate of potash, and the mass, which melted quietly, 
was maintained for seven minutes longer in a state of fusion ; hot 
water was then added till the fluid amounted to 20 cubic inches, 
and when cold it was filtered. The filtrate was acidulated with 
hydrochloric acid, then neutralized with ammonia, the precipitate 
allowed to subside, and the liquor poured off; after this, the 
precipitate, which was frequently coloured by manganese, was 
shaken with caustic ammonia and filtered. I had taken somewhat 
more ammonia than would have been required to remove from 
the precipitate an amount of 10 per cent. of tungstic acid. By 
* From the Bulletin of the Academy of Sciences of Munich, Meeting of 
March 10, 1860. Communicated by W.G. Lettsom, Esq. 
