490 Sir H. Davy’s further Experiments 
Mixtures of the triple and double compounds produce 
abundance of iodine when acted on by glacial hydrophosphoric 
acid gas, but the pure double compound affords only hydro- 
ionic acid gas, and this decomposition offers the best method 
which has yet occurred to me of procuring pure hydroionic 
acid. When the two substances are gently heated together, 
Ik 
the hydroionic acid gas, which comes over in considerable 
quantities, forms a colourless solution when absorbed by water. 
I have endeavoured to ascertain the composition of the triple 
compound of potassium. Seven grains that had been dried at 
the temperature of boiling water heated to redness in a small 
crucible of platinum lost 2.2 grains. Seven grains heated to 
dull redness in a small tube of glass lost 1.7 grain ; a minute 
portion of iodine condensed in the middle part of the tube, but 
no violet vapour was observed in the upper part of it, and 
there was a very slight appearance only of moisture, so that 
the loss of weight in this last experiment, must be principally 
ascribed to the expulsion of oxygene. 
On a comparison of the results of these two analyses, it 
appears very probable that this triple compound is composed of 
one proportion of iodine about 165, one of potassium 75, and 
six of oxygene 90 ; which is a composition exactly analogous to 
that of the hyper-oxymuriate of potassa. The quantities that I 
used in my experiments were too small to render these results 
more than approximations, yet the similarity of them to those 
presented by the hyper-oxyrnuriates ought perhaps to render 
them more worthy of confidence. 
I have attempted to obtain pure triple compounds from 
solutions of baryta and lime, and from magnesia diffused 
through water, by dissolving iodine in them by lieat, and by 
