Why pressurize the contents of a gas canister

It is easy to buy canisters of gas of many sizes, e.g. as fuel when we wish to camp in the country, or for a portable welding kit. The gas will be //-butane if the gas is for heating purposes, but might be oxygen or acetylene if the gas is to achieve the higher temperatures needed for welding. 

Typically, the components within the can are gaseous at most temperatures. The typical volume of an aerosol can is about 0.3 dm3 (3 x 10-4 m3), so it could contain very little gas if stored at normal pressure. But if we purchase a canister of gas and release its entire contents at once, the gas would occupy a volume similar that of 

Care a small p indicates pressure, yet a big P is the symbol for the element phosphorus. Similarly, a big V indicates volume and a small v is the symbol for velocity. 

Robert Boyle was the first to formulate a relationship between p and V. Boyle was a contemporary of the greatest scientist the world has ever seen, the 17th-century physicist Sir Isaac Newton. Boyle s law was discovered in 1660, and states 

An isotherm is a line on a graph representing values of a variable obtained at constant temperature. 

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