472 Air. Henry on the Natural Hijlory, &c. 
difiolved, without heat, in the fame quantity 
of the vitriolic, and even with fmaller quantities 
of the nitrous and marine acids, than were 
neceflary for the folution of the aerated. The 
a&ion of the acetous acid was fomewhat lefs 
complete, on the pure than on the aerated. The 
acids were previoufly diluted with about five 
times their weight of water, except the acetous 
which was concentrated, and the Magnefian 
Earth was intimately mixed with half an ounce 
of water, and continually agitated with a glafs 
tube, till the folution was finifhed. 
Thus I have often made complete folutions 
of pure Magnefia. Eut at other times I have 
found it obftinately to refid: folution, though 
prepared, previous to calcination, in every 
refpeft, fimilar to the other, and, though, ap¬ 
parently, perfectly calcined. This for fome 
time puzzled me exceedingly; till at lad I dif- 
covered it to depend on the date of calcination, 
and that by continuing the fire for a longer time, 
this infoluble Magnefia acquired its cudomary 
folubility. Another circumdance, attending the 
calcination of Magnefia, I have always been un¬ 
able to explain. In a certain period of the 
procels, though the Magnefia were ever fo tade- 
lefs before calcination, and though it, at this 
time, fhews ro effervefcence v/irh acids, yet it 
has acquired a dilagreeable, bitter, pungent 
tide, fomewhat refembling lime. But it does 
not, like lime, or Magnefia containing that earth, 
form 
