Couple of questions from Hayek's Prices and Production

Just started reading Hayek’s Prices and Production and I have a couple of questions.

  1. Hayek says in a barter economy that interest will keep the production process from becoming to long, basically ensuring that the proper amount of consumer goods and capital goods are produced. Having a hard time visualizing how this would take place in a barter economy. How exactly does interest in a barter economy achieve this? pg. 45

  2. What does Hayek mean by elasticity of the volume of money? pg. 45,46