282 Dr. pKif.sTr,EY*5 Experiments and Obfervations 



ineafure,. of which one-fifth was fixed air, the refiduum was 

 quire as pure as the air with which 1 hegan the experiment, ths 

 tell with nitrous air, in the proportions above-mentioned^ 

 giving. 4 in both caies. To what circumftance the. difference 

 mip'ht be ovvino- 1 cannot tell. 



In thefe experiments the fixed .air miifl:, I prefume, have been 

 formed by the union of the phiogifton from the iron and tho 

 dephlogifticated air in which it was ignited; but the quantitjj 

 of it was very imall-in proportion to the air which had difap- 

 peared, aiKl at that time Ihad no fufpicion that the iron-, which, 

 had been melted, and gathered into round balls, could hav*5 

 imbibed it ; a melting heat having been fufhcient, as I had 

 imagined,, to expel every thing that was capable of affuming 

 the form of air from any fubRance whatever.- I was therefore 

 intirely at a lofs about wl:^at raufthave become of the air. 



Seniible, however, that- fuch a quantity of air mufl have- 

 been ivrxSihtdhy fomething to which.it muft^have given a very. 

 perceivable addition of weighty and feeing^ nothing elfe that 

 could have Imbibed it,: it occurred' to me to weigh the calx into 

 which the iron had been reduced; and I prefently found, that 

 the dephlogiiliicated air had adually been imbibed. by the melted 

 iron, in the fiirDe manner as inflammable air^ in., my former 

 experiments, had been. imbibed by the melted calces of metals, 

 however impofiible fuch an abfbrpxion- might have appeared to 

 xnt a priori. In the firfl infl:ance,„ about twelve ounce mea- 

 liires of d^phlogiilicated air had difappeared,. and the iron had 

 gained -fix grains in weight, Repeating the experiment very 

 frequently, I always found, that other quantities of iro;i, 

 treated in the fame ma.iiner, gained limilar additions of weighty, 

 which \yas always very, nearly that of the air which had dif- 

 a-ppeated*. 



This 



