I've only seen snap freezing done using liquid nitrogen.  The isopentane 
can be stored in a nalgene bottle, and a nalgene cup can be used.  Pour 
the liquid nitrogen into  a wide mouth  plastic cup, and lower slowly 
into the liquid Nitrogen.  When white plaques start forming on the 
bottom of the cup, it is cold enough to snap freeze the tissue in a cryo 
mold.

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