A SIMPLE AND INEXPENSIVE DEVICE FOR FREEZE-SUBSTITUTION AT 183-K -90-C

The freeze substitution device described here consists of commonly ava ilable materials, is easy to construct and to handle and provides maxi mal working safety. An adequate mass of copper and/or brass, serving a s holder for 16 cryovials, is chilled to liquid nitrogen temperature. The vial holder is placed in a precooled thermos flask filled with eth anol and stored in an ultrafreezer at 193 K/-90 C. This ensures that t he vial holder maintains temperatures of about 183 K/-90 C for more th an 12 hr to minimize the risk of ice recrystallization.