19 Hot and Cold

CHAPTER NINETEEN HOT AND COLD Chemical bond (noun). This is the force that holds two atoms together. There are different kinds of bonds, and they can be broken and reformed. Think of it like a bunch of kids holding hands playing Red Rover. They let go of each other's hands and sometimes find new partners. WHEN BIRDIE AND I WALKED INTO MY HOUSE, it was oddly quiet. No loud screaming or thundering feet of twenty kindergartners slamming into furniture. "They must be eating," I said as we headed into the kitchen. Sure enough, Liam sat with his friends at a long folding metal table draped in a tablecloth dotted with planets. The boys and girls were finishing up their lunch, which were little pizza bagels that looked like flying saucers. There were also slices of lunchmeat cut into the shape of crescent moons and stars. "Hi!" I said. "I'm back!" "Yay!" cried a bunch of kids. A girl with two small pigtails shouted, "Spin me, Kate!" "And me!" cried Liam.

"Well, not right now," said Dad, who was by the fridge filling up a pitcher with more water. "Since you all need to finish your lunch so we can eat ice cream cake." "Cake!" Liam cried, and my heart sank. "Cake! Cake! Cake!" the rest of the kids chanted along with him. I looked at Birdie, and she looked at me. "I can't wait to see this masterpiece," said Mom, who was wearing a SPACE CREW T-shirt just like me and Dad. I bit my bottom lip. "Well, about that. You will see the cake. But just a little later." Then I explained how I had just missed Mr. Arvanites and that we could pick up the cake before dinner. "No ice cream cake for my party?" asked Liam, his voice wobbling. He blinked, and I was afraid he would start to cry. "Actually, you will still have ice cream. But it won't be a cake. Instead, you will have... astronaut ice cream," I announced. A bunch of kids, and my parents, stared at me in amazement and confusion.

"Using some awesome chemistry skills," I said in my most enthusiastic voice, "we're going to make futuristic astronaut ice cream. With liquid nitrogen." There was silence, and then suddenly the room erupted into cheers. My mom raised her eyebrows in concern. "Kate, are you really sure about this?" "She did make ice cream last year for her project," said Dad. "Oh, I'm very sure," I said. "Let's get ready. Because it's time for the coolest ice cream ever!" "At least we've done this one before," said Dad. "I'll go grab the liquid nitrogen from the garage. Operation Make the Atmosphere of Jupiter was a huge success, and we have plenty of liquid nitrogen left over." "See?" whispered Birdie. "It's all working out." "It is," I agreed. Soon enough Dad, wearing his safety goggles and gloves, came back with the dewar of liquid nitrogen. A dewar is an awesome vacuum-insulated container that keeps the liquid nitrogen nice and cold so that it doesn't boil away. "So, everyone, nitrogen is usually a gas," I explained, "but when it's chilled under high pressure, it becomes a cold liquid. And when I say 'cold,' I mean arctic cold. That's why we need to be super safe."

"With these." Dad pointed to the safety goggles he was wearing with one of his blue cryogenic gloves. Those are special gloves that scientists wear to protect their hands from extreme temperatures. "It's important to be careful since the liquid nitrogen is negative one hundred and ninety-six degrees Celsius," said Mom, who helped me grab ingredients for the ice cream: whole milk, sugar, salt, chocolate syrup, mint extract, and vanilla. Plus mixing bowls, measuring cups, and spoons. "So nobody can touch that dewar of liquid nitrogen," added Mom. "Not even us," I added as I ran to grab goggles and gloves from the basement. Birdie was already retrieving our matching blue lab coats from the mud room. After putting on my safety equipment, I set the two mixing bowls on the counter, one for me, one for Birdie. I also pre-measured out one cup of sugar for each of us. Luckily, we had two sets of measuring cups. "It's going to be incredible," gushed Birdie. "Wait till you astronauts taste all of the little crunchy shapes." "I scream, you scream, we all scream for ice cream," shouted Dad.

The kids all started screaming, with Liam yelling the loudest. "Thanks, Dad," I joked. Putting my fingers to my lips, I motioned for them to be quiet. The hollering and cheering continued. "No ice cream until you're quiet," said Birdie. Suddenly, there was silence. Mom gave Birdie a thumbs-up. "You could become a principal someday if you wanted," she said. "Okay, everyone, we're going to have some fun with chemistry," I announced. "All of you are about to eat astronaut ice cream." I turned to Dad and Birdie. "You guys ready?" "Oh yeah," said Birdie, who, just like me, stood in front of giant blue mixing bowls. "First thing we need to do is add the sugar," I said, and both Birdie and I dumped our sugar into our bowls. Next we added in two tablespoons of vanilla. "This will spike it with flavor," I said. Birdie bent down and smelled her mixture. "Mmmm, yummy." I held up mint extract. "In mine, I'm squirting one teaspoon of mint extract. So we'll have options. Vanilla and mint astronaut ice cream." And then I grabbed the carton of salt. "Where's our birthday boy?"

Liam jumped up. "I'm here!" I poured some salt into my cupped hand. "Take a pinch, Liam, and toss some into both bowls." Liam dramatically pinched his fingers together. "I'm a space lobster!" he cried. "Just don't be a greedy lobster. Then you'll be shellfish," Birdie joked. After I stopped giggling, I explained to everyone why you needed to add salt. "It lowers the freezing point," I said. "That allows the milk mixture to get nice and cold without freezing, which is what we need for ice cream. Right now, I want everyone to make a giant whoop if you are ready to get started." "Whoop whoop!" the kids cried. "And now we're going to add a third of a gallon of whole milk. It has to be whole milk. None of that low-fat stuff." I made a silly face as Mom handed me the gallon of whole milk and I poured a third of a gallon into each bowl. "We need the fat to give the ice cream its creamy texture. Otherwise, the sugar-milk mixture would turn into a giant iceberg when it interacts with the liquid nitrogen." "Can we eat the ice cream now?" lisped a girl with one missing front tooth. "Almost! We need to get all of the ingredients mixed together and then add the liquid nitrogen so our