nitrms Acid and nitrous Air. 303 
air is nearer the ftate of phlogifticated air than nitrous acid or 
nitrous vapour; and that dephiogifticated nitrous air is ftill 
nearer. It is very difficult to decide with certainty what the 
changes are which the particles of the acid undergo in their 
paffage through different parts of the hot tube. 
From what has been faid, the mold common procefs will 
probably appear to be, that a particle of the acid in the form 
of vapour firft generates nitrous air ; that the parts of this are 
applied to freffi furfaces of hot iron, and fuddenly changed into 
dephiogifticated nitrous air; which, laftly, is applied to ftill 
freffi furfaces of the tube or fragments of iron, and fo con- 
verted into phlogifticated air. When thefe fucceflive contadts 
with freffi furfaces of hot Iron are not fufficiently numerous or 
exadt, it is not unnaturaFto conclude, that fame portion of air 
may efcape not perfedtly decompofed. 
6. Thefe conliderations induced me to alter the procefs a 
little, Inftead of boiling the acid in the retort, I put fome 
thin pieces of copper into a phial, poured nitrous acid upon 
them, and forced the nitrous air, as it was generated, to pafs 
through the red-hot tube. The event anfwered my expedi- 
tion ; the decompofition was effedted in this way eafier than in 
the former. 
But before I made this experiment, I examined what would 
be the effedt of mere heat upon nitrous air, as I had already 
learned from the experiments of others, that nitrous acid, 
forced in the form of fteam through red-hot tubes of clay or 
glafs, underwent the moft important alterations. 
What might be the effedt of long continued expofure to a 
red heat I cannot fay ; but I was foon convinced, that nitrous 
air might be forced through a red-hot glafs tube, without 
fuffering any material change. 
% x % 7. Laftly, 
