Rechargeable Desiccant Kit comes with four desiccant cartridges. Rechargeable desiccant cartridges are contained in rigid metal cages which are user-installable. Two cartridges are required for Spectrum One and Spectrum One NTS spectrometers. It is recommended to have spare desiccant cartridges available so when a desiccant change is required recharged desiccant can be installed immediately.