First, the extinguisher valve is removed and the threads and interior of the cylinder are checked for corrosion, pitting, and any other abnormalities. [29 CFR 1910.157(f)(3)] If the cylinder passes the visual inspection, it is placed into a steel chamber, which is then filled with water at normal pressure.
Updated April 17, 2017. The earliest dated printed book known is the Diamond Sutra, printed in China in 868 CE. However, it is suspected that book printing may have occurred long before this date. In 1041, movable clay type was first invented in China.
Of course Hill's proposal was heavily debated for a few years, but after serious discussion the change was enacted and instituted in 1840. Thus on May 6, 1840 (first date of valid use) the first government-printed postage stamps were born. Sir Rowland Hill himself designed the first stamp which cost one penny and bore the profile of Queen Victoria.