and Ohsefvations on Iodine, 
495 
whicli it is used cloudy like the hydrosulphurets by the de- 
position of solid matter, and it does not enlarge the volume of 
the residual air like some other substances. 
The solution of the hydroionic acid is decomposed by being 
heated with the hyperoxymuriate of potassa, and iodine is 
produced. 
Hydroionic acid gas, as I have mentioned in my last paper, 
is decomposed by all the metals I have exposed it to, except 
gold and platinum ; and the same metals that decompose it 
in its gaseous state, likewise decompose it when it is in solu- 
tion, requiring, however, in some cases, the assistance of heat. 
The fluid hydroionic acid tarnishes silver at common teni- 
peratures, and dissolves mercury slowly when boiled in contact 
with it. 
2 . It dissolves the alkaline and common earths, and forms 
with them compounds very analogous in their properties to 
the compounds they produce when acted on by muriatic acid. 
I heated dry quick lime in a small tube filled with hydro- 
ionic acid gas, a yellow fluid immediately formed, which was 
coloured by dissolving hydroionic gas and iodine, and a fusible 
compound soluble in water, and which had a bitter taste si- 
milar to muriate of lime, was produced. 
I made the same compound by dissolving marble in the 
hydroionic acid ; the compound when heated to redness be- 
came fluid, and when kept in fusion in contact with air emitted 
iodine, gradually lost its fusibility, and from being neutral 
became alkaline, so that at a high temperature iodine is partly 
expelled from calcium by oxygene. I proved this still more 
distinctly by fusing the compound in a close vessel, in which 
it was confined by mercury. There was no change. I ad- 
3 S 2 
