Re: "Cheap" vacuum
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Fill the box with steam, and then freeze it?
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Theory says that should get you to 6 millibars (0.6 kilopascals). Brian -- If he has a 5 liter box at a 1,013.25 millibars, and he wants to
get to 10 millibars, wouldn't he need to attach a completely empty 511.625 liter vacuum chamber to it in order to get both the box and the vacuum chamber to equalize at 10 millibars? Finding and evacuating a 136 gallon vacuum chamber (or larger if he can only evacuate it to a few millibars) might not be all that cheap. If freezing it is difficult where there is no electricity, perhaps filling the box
with molten lead, and then emptying it through a 3 foot pipe in the bottom might work. The weight of the molten lead would leave a vacuum as it poured out into a holding basin, much like the original mercury barometers. Lead/tin
solder could also be used, to get a lower melting point, but he would need a longer pipe, since the density is 8.79 instead of leads 11.34. 5 liters of solder weighs a little under 100 pounds. At $6 per pound for 80/20
lead/tin solder, that's $600.00. He could get a cheap vacuum pump like the ones they use to reclaim Freon from car air conditioners for about $100, and an inverter for a car for about
$20 (to convert the car's 12 volts DC into 120 volts AC). It might take all day for the pump to do the job, but it's cheaper than lead. ;-) ----- Get a free science project every week! ""On Mon, Jun 6, 2011 at 3:14 PM, brian whatcott <betwys1@...> wrote:
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Simon Quellen Field