I would say good luck, and bring a mop. <img src="/images/graemlins/smile.gif" alt="" />

How are you going to regulate the tempurature of your rocks when you are heating them by fire? Anything you are likely to have you will give you the same results as your fingers- "hot! really hot! OWWWW!" <img src="/images/graemlins/smile.gif" alt="" /> I'm not mocking, I'm just making a point- I can't see how you can keep the tempurature regulated enough that you wouldn't deform the bottle, which would destroy the seam, and that is completely ignoring everything that is published about safe tempuratures and lexan.

Actually, I can see one way. Use wire to suspend a heated rock in the middle of the lexan container. But the rate of heat lost fromt eh rock and the total energy it could hold might be problematic. You'd be better off with something like a 1-3/4" sphere (should fit in a wide mouth nalgene) of iron, heated red hot, on the end of a long steel pole.

I can't see that being practical- it would be probably three or four pounds, and for that weight, you can bring a soda stove and a couple pints of dry gas. It also isn't using a rock. I think you are going to find two things- one, you will deform the polycarb in one manner or another by placing the rocks into the bottle unless they are suspended so they don't come into contact with the bottle, and two, IF you can get it to boil without utterly destroying the bottle, you will have almost as much, if not more, rocks than you do water.

And I've never seen it done in a canvas container, and my origami skills suck so much that I can't even make a paper cup that doesn't need paper clips to stay together. Now, I have done it with paper clips, but the paper is definantly a little more the worst for wear around them if I'm boiling over a fire. Never tried putting a hot rock into a paper container, but I have into hard shelled goards, a cocanut shell and an orange rind with a fair degree of happiness (other than there is a rock in my little goard, which means less soup).