Our shopping list this week:

• orange marmelade
• cream cheese
• parmesian cheese
• toothpaste
• coffee
• stapler
• frozen peas
• pepperoni
• liquid nitrogen

My brother had his 40th birthday party last week. My gift to him was to supply liquid nitrogen ice cream for all the guests. I've been wanting to try LN2 ice cream for years, but didn't know how or where to get my hands on the stuff. In grad school we just had a tank of the stuff in the lab. It was supposed to be for experiments, but a significant percentage was diverted for various graduate-level entertainments.

About a month ago one of the other geek dads at the twins' school served LN2 ice cream at his son's birthday party. The primary reason for enrolling one's children in a Gifted and Talented program is, of course, getting to socialize with geek dads.

I interrogated him and found out that, as long as one has the right equipment (a liquid nitrogen storage dewar), LN2 is easily obtained from your friendly local welding supply store. The nitrogen itself isn't too expensive, though the dewar is a few hundred dollars. On the other hand, the dewar will last for decades if properly cared for, so a one-time investment can mean years of uniquely nerdy party entertainment at a very reasonable price. My brother's milestone birthday gave me just the excuse I was looking for.

Unfortunately, we emptied the dewar before the kids got tired of ice cream. One of the twins (age 10) decided that more LN2 was an essential household supply.

And that is why we are the only family on the block with "liquid nitrogen" on our grocery list.

Now if you will excuse me, I need to go load the dishwasher and check on the cryo-tanks.