406 Berzelius on a neve Mineral Body, [JUNE, 
the .seleniate of tin, I thought it necessary to examine what 
could be the cause of this. .1 dissolved it in a little water, and 
added to it caustic ammonia. It was scarcely rendered muddy, 
and the acid which remained had a metallic taste. The same 
thing happened when I saturated the acid with carbonate of 
soda. I mixed a third portion of the acid with caustic potash ; 
a copious, heavy, lemon-yellow precipitate fell; but the alkaline 
liquor still retained a little of its metallic taste. r 
__e. The yellow precipitate did not change its colour on drying. 
It was volatilized before the blow-pipe. | I introduced it in con- 
sequence into a glass retort, and distilled it ata red heat. It 
gave out at first water, and when the retort began to get red, 
running mercury. In the retort remained some traces of oxide 
of tin. The seleniate of potash being evaporated to dryness and 
distilled in a retort at a red heat gaye still some drops of running 
mercury. 
f. The seleniate of potash remaining at the bottom of the 
retort. was fused: on cooling, its colour became white. The 
retort was broken,. and the salt reduced to powder, and mixed 
with its own volume of sal ammoniac in powder. This mixture 
was introduced into a retort, and exposed to,a graduated heat. 
Water was first disengaged containing ammonia, then traces of 
selenium condensed in the neck of the retort and in the receiver, 
and the excess of sal ammoniac began to sublime. The retort 
was, left still some time exposed to the heat, and then withdrawn: 
Water being poured into the saline mass remaining in it, the 
salt was dissolved, leaving for residue a coarse brown powder, 
which was selenium reduced. It was. dried and distilled in a 
small retort but to purify it completely and to procure it ina 
cohering mass. The reduction of the seleniumis occasioned by 
the production of seleniate of ammonia, as well as by the disoxy- 
genizing action of the hydrogen of the ammonia on the selenic 
acid. As selenic acid saturates more ammonia than its oxygen 
is capable of decomposing, there is disengaged in this operation 
a portion of ammonia with the azotic gas. 
-g. The white mass, spotted red, which remained at the bottom 
of the retort (in e), consisted chiefly of seleniate of barytes, part 
of which could be removed by water; of seleniate of tin; sele- 
niate of copper; and arseniate of barytes, known by the disen- 
gagement of vapours of arsenic when treated by the blow-pipe: 
[t results from these experiments that the selenium in the 
sulphur examined is accompanied by at least seven other metal- 
lic bodies ; namely, mercury, copper, tin, zinc, iron, lead, arsenic: 
The process for insulating the selenium will appear rather long, 
and [ have since found methods of rendering it shorter. But I 
have chosen to describe it such as I practised it; because it 
guarantees the absence of sulphur, arsenic, and mercury. The 
sulphur was separated by the muriate of barytes ; the arsenic 
remained in the state of arseniate of barytes when the selenic 
