How much does a cubic foot of nitrogen weigh?

Lithium is a bit more than half as dense as water. Its relative density -- or, if you prefer, specific gravity -- is 0.53. So, if you know how much a cubic foot of water weighs, multiply that value by 0.53. BTW, one gallon of water (at 4 degrees C) weighs 8.34 pounds, and one cubic foot of water contains 7.48 gallons. (I know that because WikiAnswers told me.) Now you've got all the info you need to make the calculation.