It says: "by heating isoamyl
nitrate with phosphorus pentoxide (E. T. Chapman and M. H. Smith, Ann., 1868, Sup p1. 6, p. 329)". Nitrate is not the same as nitrite. You can't get any nitrate from any poppers. Nitrates are esters of nitric (V) acid while nitrites are esters of nitric (III) acid. Amyl nitrate is n-pentyl nitrate [ CH3-(CH2)4-O-NO2 ] while isoamyl nitrate is isopentyl nitrate [ (CH3)2CH-(CH2)2-O-NO2 ]. The problem is that both amyl and isoamyl are used completely wrong so often isoamyl is the same as amyl and amyl the same as isoamyl (trivial names sucks).
Just the thought that somebee wants to waste something so useful as P2O5 just to produce pyridine breaks my heart.
Edit: I have checked and both, amyl and isoamyl, are supposed to bee trivial names for isopentyl. But n-pentyl is also called n-amyl in some cases.