282 Dr, Pri estley’s Experiments and' Obfervatiom 
meafure, of which one-fifth was fixed air, the refiduum was* 
quite as pure as the air with which I began the experiment, the 
teft with nitrous, air, in the proportions above-mentioned, 
giving .4 in- both cafes. To what circum fiance the. difference 
might be owing I cannot tell. 
In thele experiments the fixed air muff, I prefume, havebeena 
formed by the union of the phlogiftom from the iron aird the 
dephlogifticated air in, which it- was ignited ; but- the quantity 
of it was very final l in proportion to the air which had difap- 
peared, and a.t that time Lhad no fufpicion that the iron, which 
liad been melted, and gathered into, round halls, could have 
imbibed it ; a. melting heat having been lufRcient, as I had 
imagined,, to expel everything that was capable of aftuming 
the form* of air from- any, fuhfiance whatever. I was. therefore 
intirely at; a lofs about what- muff have become, of the air. 
Senfibly however, that fuch, a. quantity of air muff have 
been imbibed by fomdhmg to which it muff , have given a very 
perceivable addition of weight, and feeing nothing el-fe that 
could have fmbibed-it; it' occurred to me to weigh the calx into 
which , the iron - had 'been reduced n and p refen tly found, that, 
the deph logifticated air liad adtually. be<?n imbibed by the melted ■ 
iron, in the fame manner as- inflammable air* in my former 
experiments, had been imbibed by the melted calces of metals, 
however impoffible fuch an abforption might have appeared to 
me a priori. In the firft inftance,. about twelve ounce mea- 
futes of dephlogifticated air had difappeared, and the iron had 
gained -fix grains in., weights,-, Repeating the experiment very 
frequently, I always found, that other quantities of: iron, 
treated in the fame manner, gained fimilar additions of weight, , 
which was always very nearly that of. the air which had . dif- 
o*. - 
This 
