Subject: Why does acetone boil in a dry ice env. after putting some material in it?

I am asking this question because me and my friend couldnt find an explanantion 
for this occurrence. This happens when we are doing pretreatment experiments 
for toxicokinetic analysis. The actual condition is acetone is poured in a 
metal container (only acetone) and placed in styrofoam full of dry ice. The 
temperature of the acetone drops to -70 C. we actually measured this with a 
thermometer working on this range. when we put the test tubes to separate the 
aqueous layer from the organic layer. thats when we notice some bubbles  
forming in the glass surface. the temperature of the test tube is about 4 C 
because it centrifuged prior to extraction. i could say the test tube is hot as 
compared to a -70 C. 

Re: Why does acetone boil in a dry ice env. after putting some material in it?