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New type of DIY CO2 proposed


I am thinking of designing a new type of DIY CO2 setup: using a bottle with
dilute muriatic acid and pieces of marble in it. This should be cheap and
can produce lots of CO2. Since marble is rather dense, and 
one can use very dilute acid, it can be set up so that the reaction will
last for quite a period of time. 

Below are some calculations based on what I remember from my chemistry
classes at school (over 15 years have passed since then... Please forgive
and correct me, if I am wrong) Well, considering a bubble rate of one
bubble per second, with a bubble size of 0.1 inch (well, these are very
rough calculations, and I consider
cubic bubbles - it doesen’t matter much, anyway), we will need about 2,600
cu.in of CO2 per month - or roughly, two mols. The reaction is following:

CaCO3 + 2HCl = CaCl2 + CO2 + H2O

Considering molar weights of used substances, we’ll need 200 grams of
marble and about 150 grams of HCl to produce one months worth of CO2. I
guess, the substances can be filled in a 2 liter coke bottle, 
similarly as with the yeast method. Depending on the marble granule size
and how dilute acid will be used, the reaction can be slowed down or
intensified. I guess, the larger the granule size and the more dilute acid
used, the slower will be the reaction. The output CO2 can be bubbled
through a second bottle with chalk water (something like what people spray
on the ceiling, but without glue added) to eliminate possible contamination
of the output CO2 with acid vapors. 

Anyone would like to experiment with this setup? Any other ideas? 

- Vahe