contained in the Bavarian Tantalite. 359 
Pelopic acid, and the metal Pelopium, from Pelops, the son of 
Tantalus, and the brother of Niobe; to point out, at the same 
time, by this name, not only its simultaneous occurrence with 
the oxyd of niobium, but more particularly the very great re- 
semblance of pelopic acid to the tantalic acid from the Finland 
tantalites. ‘This similarity is indeed more perfect than exists be- 
tween the combinations of any other two simple metals; it is so 
great, that it was only after a long-continued and most minute 
investigation that I could decide upon publishing the results I had 
obtained e combinations of niobium are, on the contrary, 
very different from those of pelopium or tantalium. 
I will here describe the most important properties by which 
the compounds of tantalium differ from the corresponding com- 
pounds of pelopium, and at the same time enumerate those of 
niobium. 
In its properties, pelopic acid is intermediate between tantalic 
and niobic acids, just as strontia is between baryta an ime. And 
in the same way as we are able to explain many properties of 
strontia, by assuming it to be a mixture of the two last-men- 
tioned earths, we are able to determine @ priori most of the pro- 
perties of pelopic acid, by admitting it to be a mixture of a large 
proportion of tantalic acid, with a small quantity of niobic acid ; 
and as was the case with bromine, which, on its discovery, was 
considered to be a combination of chlorine and iodine, I my- 
self was long of opinion that the pelopic acid was nothing more 
than tantalic acid, still contaminated by a certain quantity of ni- 
obic acid, which I had not succeeded in separating. It was only 
by an uninterrupted investigation of this subject for several years 
that I became convinced of the distinctness of pelopic acid. 
The chlorids of the three metals dissolve in cold concentrated 
# 
whole of the niobic acid is precipitated from the solution. — 
. id issolves in hydrochloric acid in the 
cold to a turbid liquid, which after some length of time forms an 
opaline jelly, from which water both cold and boiling dissolve only 
aces of tantalic acid.—But if chlorid of tantalium is treated 
with boiling hydrochloric acid, it does not dissolve entirely, and 
on cooling it does not form a jelly, but water now dissolves the 
whole of it to an opaline liquid, which is not rendered more tur- 
bid by boiling. Sulphuric acid produces in it, after some time, 
4 voluminous precipitate even in the cold. The chlorid of pe- 
lopium behaves in a similar manner, except that sulphuric acid 
