During the US Civil War, saltpetre was collected from caves to make gunpowder; it used to be thought that this was bat guano, but most of the nitrate comes from nitrifying bacteria.
În timpul Războiului Civil American, saltpetrul⁠(d) era extras din peșteri pentru a produce praf de pușcă; se credea că acesta era guano de lilieci, dar majoritatea acestor nitrați provin de la bacterii azotificatoare.