Prof. F. von Kobell on Dianic Acid, 419. 
recourse must be had to an assay with sulphuric acid and zinc to 
determine between these two acids. I am at least inclined to think 
that our determinations, as far as correctness is concerned, will 
have as great a probability in their favour as with the other 
methods hitherto employed, which, as is shown by the constantly 
varying indications of the acids of euxenite, yttrotantalite, 
samarskite, &c., have not given any thoroughly reliable results. 
With respect to the acid discovered by me, and which forms a 
blue solution with hydrochloric acid and tin with such remark- 
able facility, it is with certainty and ease distinguishable both 
from tantalic and from hyponiobic acid, and that evidently in 
a more marked manner than those acids mutually are; the me- 
thod of its preparation, moreover, as above set forth, as well 
also as a comparison with kindred acids under closely similar 
circumstances, appear to me to exclude the idea of its being an 
allotropic state, or a not hitherto observed stage of oxidation of 
tantalum or niobium, and to claim for it an existence as a distinct 
acid. Hermann, as is well known, several years since assumed 
the occurrence in samarskite, formerly termed uranotantalite, 
of a peculiar acid which he termed ilmenic acid; he was, how-. 
ever, not enabled to characterize that acid with sufficient pre- 
cision; and Heinrich Rose could at that time establish point by 
point for his own niobic acid, now termed hyponiobic, everything 
that Hermann sought to establish for ilmenic acid, so that at last 
Hermann ranged his acid under niobium, and has pronounced 
it to be a niobous-niobic combination*. That the acid discovered 
by me is an oxide of niobium is, as far as present experience 
-goes, not to be assumed ; for if it were a lower grade of oxidation 
than the hyponiobic acid we are acquainted with, it must, on 
being fused with potash in an open crucible, be converted to 
this hyponiobic acid, inasmuch as, according to Heimrich Rose, 
niobium itself is dissolved into hyponiobate of potash by boiling 
potash ; and if it were a higher oxide than hyponiobic acid, it 
must, on being reduced with tin, be also converted into that 
acid, and consequently neither soluble in hydrochloric acid 
‘under the conditions spoken of, nor impart a blue colour to the 
solution, as is, however, the case. 
The same argument holds good if it be regarded as an oxide 
of tantalum: under the treatment referred to, it must be con- 
verted into the tantalic acid with which we are familiar, and 
must agree with it in its reactions, which it does not. Hein- 
rich Rose has duly established that the metallic acid of the 
tantalite of Bodenmais is distinct from that of certain Finland 
tantalites; and to mark the difference, he called the former 
* According to Hermann, it colours salt of phosphorus dark brown 
before the blowpipe. 5 
2K2 
