hcl is a reagent
what do u mean by white fumes due to hcl ??
is there something else also which creates dense white fumes with HCl? idk.. but NH4Cl is the most frequently used when reacted with HCl .right...and here that is the one in the picture imo. Pls share if u think something else can also create white fumes here. @Mayank_Chowdhary
Nitrides form here when reacted with Air in 1st step