196 Continuation of the Experiments and Obfervations 
is difengaged from them, it appears in a fluid and elaflic form, 
and is then commonly called inflammable air. Thefe different 
ftates of the fame fubftance arife, according to the immortal 
difcoveries of Dr. black, from the different portions of ele- 
mentary fire contained in fuch fubftance, aad ablorbed by it, 
whilft its fenfible heat remains the fame, and hence called its 
Jpecific fire. For want of attention to thefe different ftates, the 
very exiftence of phlogifton as a diftindl principle has been 
frequently called in queftion,, and chemifts have been required 
to exhibit it feparate in its fixed ftate, without recollecting, 
that neither can fixed air be fhewn feparate in a concrete ftate, 
nor that phlogifton may alfo be in the fame predicament ; while 
others have totally miftaken the nature of inflammable air, 
and imagined it to be a combination of acid and phlogifton. 
The reafon why fixed air cannot be feparated from any fub- 
ftance in a concrete ftate is, beca ufe when it is feparated, for 
inftance by means of an acid, there is qjways a double decom- 
pofition, the acid yielding its fpecific quantity of fire to the 
concrete fixed air, which then- aflumes an aerial form, while, 
the fixed, air yields the fubftance k was combined with to the 
acid. This is lo true, that though a foliation of lime in the 
nitrous acid yields a conliderable quantity of heat, yet a folu- 
tion of chalk in that acid fcarcely yields any; for all the fire 
that is let loofe, and rendered fenfible in the firft cafe, is ab- 
forbed by the fixed air in the fecond cafe, being precilely that 
which converts it into an aerial form. The feparation of phlo- 
gifton from a metallic earth in the form of inflammable air 
arifes from the fame caufe, the diflolving acid yielding its fire 
to the phlogifton, which then aflumes an aerial form, while 
the phlogifton yields the metallic earth to the acid. It is true, 
that much fenfible heat is produced on this occafion, for which 
three 
