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I was very entertained by Hans de Grys’s article on determining the pressure in an unopened can (1), and have spent some thought on alternative ways of going about this, particularly to see if it can be done without even opening the can. Here is an experiment that I have done that gives a result within the ball-park of the pressures quoted. The temperature was 20 °C. I set up a horizontal wooden strut of 10 mm width, then hung the can of Sprite centered horizontally across it, with a weighted plastic bag hanging below by its outspread handles—which both kept the can in place and slightly compressed the side where the can contacted the strut. In order to measure the length of contact of the can with the strut while weighted, I placed some wet paint on the strut. Here are the results: Contact area = 10 mm × 8 mm = 0.124 sq in. (error about 10%) Mass of can + weights = 4.375 lb Pressure = mass/area = 35.3 lb/sq in. (cf. the quoted values—higher than 20 psig and up to 55 psig at room temperature).
I have not corrected for the strength of the empty can, which is very small. This will reduce the measured pressure below 35 psig. I have also devised another gedanken experiment that I believe might work. Immerse the can a little off vertical in water and pierce the side vertically with a sharp hypodermic needle attached to a volumetric syringe of about 20 mL. (The needle should only penetrate into the head-space gas, and not so deep as to get into the liquid.) The pressurized gas should then escape into the syringe, to atmospheric pressure, when its volume can be determined. The purpose of the immersion of the can in water is to check for leakage outside the needle—which, I guess, should be small if the can is rapidly pierced and without any sideways motion. Literature Cited- de Grys, Hans. J. Chem. Educ. 2007, 84, 1117–1119.
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