Riddle: A man is having a party for his Mom. It is a wine party. There are 20 bottles of wine. One of the wine bottles has acid instead of wine, because it got mixed up with an incoming shipment for the local laboratory. How does the man find out which bottle has acid in it?
Answer: He pours wine from each of the 20 bottles in to styrofoam cups and labels the bottles and the cups 1-20. Whatever cup melts first you find the corresponding number, and you throw both out.