4 0 ▁F ) ▁for ▁one ▁hour ▁or ▁two ▁hours ▁at ▁a ▁temperature ▁of ▁ 1 6 0 ▁C ▁( 3 2 0 ▁F ). ▁D ry ▁heat ▁ster il ization ▁can ▁also ▁be ▁performed ▁at ▁ 1 2 1 ▁C , ▁for ▁at ▁least ▁ 1 6 ▁hours . ▁ ▁Chem ical ▁ster il ization , ▁also ▁referred ▁to ▁as ▁cold ▁ster il ization , ▁can ▁be ▁used ▁to ▁ster il ize ▁instruments ▁that ▁cannot ▁normally ▁be ▁dis in fect ed ▁through ▁the ▁other ▁two ▁processes ▁described ▁above . ▁The ▁items ▁ster il ized ▁with ▁cold ▁ster il ization ▁are ▁usually ▁those ▁that ▁can ▁be ▁dam aged ▁by ▁regular ▁ster il ization . ▁Comm only , ▁gl ut ar al de hy des ▁and ▁formal de hy de ▁are ▁used ▁in ▁this ▁process , ▁but ▁in ▁different ▁ways . ▁When ▁using ▁the ▁first ▁type ▁of ▁dis in fect ant , ▁the ▁instruments ▁are ▁so aked ▁in ▁a ▁ 2 – 4 % ▁solution ▁for ▁at ▁least ▁ 1 0 ▁hours ▁while ▁a ▁solution ▁of ▁ 8 % ▁formal de hy de ▁will ▁ster il ize ▁the ▁items ▁in ▁ 2 4 ▁hours ▁or ▁more . ▁Chem ical ▁ster il ization ▁is ▁generally ▁more ▁expensive ▁than ▁steam ▁ster il ization ▁and ▁therefore ▁it ▁is ▁used ▁for ▁instruments ▁that ▁cannot ▁be ▁dis in fect ed ▁otherwise . ▁After ▁the ▁instruments ▁have ▁been ▁so aked ▁in ▁the ▁chemical ▁solutions , ▁they ▁are ▁mand atory ▁to ▁be ▁r ins ed ▁with ▁ster ile ▁water ▁which ▁will